Electronics Material Officer Course
MODULE NUMBER FOUR
LESSON TOPIC ONE
COMMUNICATIONS SYSTEMS/EQUIPMENTMODULE FOUR LESSON TOPIC ONE
LESSON TOPIC OVERVIEW
LESSON TOPIC ONE
This lesson topic presents information common systems and equipment used in naval telecommunications.
The LEARNING OBJECTIVES of this LESSON TOPIC are as follows:
4.1 Describe shipboard Combat Systems Electronic Communications equipment as related to:
b. Physical characteristics
j. Other electronic subsystems
k. Technical documentation
l. Material condition
4.2 Identify common types of communication antennas to include:
b. Relationship of length to frequency
4.3 Describe the basic operation and interface of communication systems to include:
a. Ultra high frequency (UHF) voice
b. Teletype (TTY) systems
c. Multiplex systems
d. Fleet satellite communications (SATCOM)
4.4 Describe the characteristics of various portable communications equipment to include:
b. Frequency range
c. Power out
d. Modes of operation
The student should review the "LIST OF STUDY RESOURCES" and read the Lesson Topic LEARNING OBJECTIVES before beginning the lesson topic.MODULE FOUR LESSON TOPIC ONE
LIST OF STUDY RESOURCES
To learn the material in this LESSON TOPIC, you will use the following study resources:
Written Lesson Topic presentations in the Module Booklet:
1. Lesson Topic Summary
2. Narrative Form of Lesson Topic
3. Lesson Topic Progress Check
1. Assignment Sheet
2. Answer Booklet
1. Shipboard Electronics Material Officer, NAVEDTRA 12969
2. Introduction to Wave Propagation, Transmission Lines and Antennas, NEETS Module
3. Modulation Principles, NEETS Module 12
4. Radio-Frequency Communications Principles, NEETS Module 17
5. NTP 2 Naval Telecommunications Procedures (UHF/SHF/EHF)
6. Navy UHF Satellite Communications System Description, FSCS-200-83
7. Tactical SHF SATCOM CD-ROM
LESSON TOPIC SUMMARY
This lesson topic will introduce you to a variety of communications systems and equipment that you may be materially responsible for as EMO. The lesson begins with a introduction to the Defense Communications System and communications/propagation fundamentals. It covers basic electronic equipment and systems, satellite communications, quality monitoring, and teletype/facsimile. The lesson also provides some technical background to assist you in understanding electronic equipment operation and describes system interrelationships and the future of U.S. Navy communications. The lesson narrative is organized as follows:
A. Introduction to Telecommunications
B. Communications Fundamentals
C. Propagation Review
D. Atmospheric Effects on Propagation
E. Communications Equipment Fundamentals
F. Communications Antennas
G. Antenna Couplers
L. Basic Communications Radio Systems and Equipment
M. Satellite Communications Fundamentals
N. EHF Satellite Communications
O. SHF Satellite Communications
P. UHF Satellite Communications
Q. Shipboard Communication Systems Quality Monitoring
LESSON TOPIC 4.1
INTRODUCTION TO TELECOMMUNICATIONS
The primary means of communicating between ships and stations is known as telecommuni-cations. Telecommunications refers to communications over a distance and includes the transmission and reception of intelligence by wire, radio, and other electromagnetic systems and equipment.
DEFENSE COMMUNICATIONS SYSTEM (DCS)
The DCS is composed of worldwide, long-haul, government owned and leased point-to-point circuits, trunks, terminals, switching centers, and control facilities of military departments and defense activities. The DCS combines into a single system all the elements that make up U.S. Navy, Army, and Air Force communications systems. The DCS is managed by the Defense Information System Agency (DISA), formerly known as the Defense Communications Agency (DCA). DISA's mission is to plan, develop, test, engineer, implement, operate, and maintain joint information systems in support of command, control, and communications. The DISA organization consists of the DISA Director, White House Communications Agency, Defense Communications System, and Naval Computer Telecommunication System. The DISA Director is a general or flag-rank officer responsible for coordinating the combined communications elements of the military departments. The White House Communications Agency provides telecommunications and related support to the President and elements related to the President. DCS subsystems provides communications between all levels of command through the use of four switched systems and a space component. The NTCS provides, operates, and maintains U.S Navy ashore communications and non-tactical information resources.
DEFENSE COMMUNICATIONS SUBSYSTEMS
Defense Switched Network (DSN)/Automatic Voice Network (AUTOVON)
The DSN/AUTOVON provides rapid, direct interconnection of DOD and other government installations through telephone exchanges. The DSN is a worldwide, general-purpose direct dialing telephone system. Eventually DSN switches will replace all existing AUTOVON switches. The difference between the two is that AUTOVON is an analog switched network and DSN is a digital switched network.
Automatic Secure Voice Communications (AUTOSEVOCOM)
AUTOSEVOCOM is a worldwide, switched telephone network that provides authorized users with the means to exchange classified information over communications security (COMSEC) equipment.
Automatic Digital Network (AUTODIN)
The DCS AUTODIN is a modular computer-controlled, automatic, and secure data communications system that converts word messages to digital format for transmission, providing instantaneous secure communications between subscriber terminals around the world. AUTODIN is a defense message switching, store, and forward system. Its switching centers are interconnected through a network of high frequency radio channels, submarine cables, microwave and tropospheric channels, and wire lines. The purpose of AUTODIN is to reduce message handling and delivery times through automation. General message traffic connectivity from DOD communications networks to fleet units is provided by the shore-based Naval Communications Processing and Routing System (NAVCOMPARS) via transmission on the Common User Digital Information Exchange Subsystem (CUDIXS) radio frequency link, Fleet Broadcast transmission, and the Manual Relay Center Modernization Program (MARCEMP) high frequency (HF) communications link to afloat units. The NAVCOMPARS is interfaced with AUTODIN switching centers to provide automatic connectivity with DOD communications networks.
Shorebased CUDIXS suites provide high speed digital data exchange using U.S. Navy SATCOM systems for ship-to-shore communications, acting as an interface between NAVCOMPARS and the shipboard Naval Modular Automated Communication Subsystem (NAVMACS), a shipboard message handling system. CUDIXS provides a communications path for sixty subscribers. NAVCOMPARS provides on-line communications interface between operational fleet, selected shore command, and other local subscribers and DISA AUTODIN switching centers for diverse connectivity. NAVCOMPARS provides the Manual Relay Center Modernization Program (MARCEMP) for automated HF message relay operations with fleet units using UNISYS Desktop III computers for tapeless communications. NAVCOMPARS also provides Personal Computer Message Terminal (PCMT) interface. PCMT is a message processing package that allows message transmission and reception using 3½" and 5¼" floppy diskettes and MTF Editor software.
Defense Data Network (DDN)
The DDN is a packaged digital switching network that provides the same function as AUTODIN. The difference between DDN and AUTODIN is that DDN processes data in packages of known quantities. DDN converts messages that have indiscriminate amounts of data into a finite size for more efficient message handling at faster data rates. DDN started as a research and development data transfer system and was adopted by the U.S. Navy to create three separate secure Military Networks (MILNET) for handling classified shore message traffic (secret, top secret, and special intelligence). AUTODIN was originally established in 1963 with a ten year life cycle and still serves as the primary backbone system for defense message processing. The Defense Message System (DMS) is planned to create a gateway between a merged DDN and AUTODIN. DDN is planned to eventually replace AUTODIN as DMS.
Defense Satellite Communications System (DSCS)
DSCS provides satellite connectivity between the National Command Authority (NCA) and the Worldwide Military Command and Control System (WWMCCS) and fleet commanders. WWMCCS provides operational direction and control of all U.S. military forces. The DSCS provides secure inter/intra-battle group communications.
Defense Special Security Communications System (DSSCS)
DSSCS was established to integrate critical and special intelligence communications into a single automated communications network, using AUTODIN switching networks. Integration of this
system into AUTODIN provides two separate systems within AUTODIN, one for special intelligence (SI) message traffic and the other for regular message traffic.
Secure Voice Network
Secure voice communications from ships are interfaced to public switched telephone networks, AUTOSEVOCOM, and/or DSN by a telephone secure switchboard operator via radio wireline interface or satellite radio wireline interface. Connectivity from shipboard phones (STU-III, Red Phones, and ANDVT) is made using DSCS superhigh frequency (SHF), International Maritime Satellite (INMARSAT), ultrahigh frequency (UHF) satellite, and HF communications links.
NAVAL COMPUTER TELECOMMUNICATION SYSTEM (NCTS)
NCTS provides, operates, and maintains U.S. Navy shore communications and non-tactical information resources and those elements of the Defense Information System assigned to the U.S. Navy. NCTS is a worldwide network of voice and data communications systems that support U.S. Navy surface, submarine, aviation, and special force users at all levels. Commander, Naval Computer and Telecommunications Command (COMNAVTELCOM) reports directly to the CNO as type commander for all NCTS activities and is responsible for their administration, maintenance, and readiness. The NCTC Naval Computer and Telecommunications Command (NCTC) is responsible for an AUTODIN switching center, Naval Computer Telecommunication Stations (NAVCOMTELSTA), Naval Computer Telecommunications Area Master Stations (NCTAM), Naval Telecommunications Centers (NTCC), and the Defense Communications Security Material System (CMS).
Naval Computer Telecommunications Area Master Station
NCTAMSs provide regional operational management of COMNAVTELCOM sites to execute Fleet Commanders in Chief's (CINC) communications requirements. NCTAMSs provide a major interface between shorebased communications and afloat units. Area master stations provide operational control of communications assets based on fleet needs, as determined by Fleet CINCs. While all NCTAMSs have similar operational capabilities, no two have identical assets. NCTAMS responsibilities include:
lEnsure the ability to fulfill all validated communications requirements in the NAVCOMMAREA.
lAssist fleet units and commanders in operation communication planning.
lConduct limited analysis of communication operations in the NAVCOMMAREA.
lCoordinate with the Fleet Telecommunications Operations Center (FTOC) for transfer of communications responsibility, retermination, and traffic rerouting for transiting fleet commands. FTOC provides real time operational direction of area communications, within the NCTAMS.
lFunction as Navy Satellite Communications (SATCOM) Network Area Control Activity to exercise operational direction and control of Navy SATCOM link terminals in the
lControl the use of assigned U.S. Navy tactical radio frequencies and disseminate interference information.
The Copernicus architecture involves a major restructuring of U.S. Navy C4I (command, control, communications, computers, and intelligence) to place the operator at the center of the command and control universe. Rather than "push" data to the battle group/battle commander, data is collected, correlated, and fused to efficiently disseminate it (only once) when it is required. Copernicus uses extant communications systems and equipment and a Communication Support System (CSS) to integrate U.S. Navy communications assets. CSS is the communications subarchitecture that provides multimedia access and media sharing, permitting users to share total network capacity on a priority demand basis in accordance with the tactical commander's communications plan. Communications pathways are automatically selected and not dedicated, making the transmission medium is invisible to the user.
A complex of links forms a major communications system. The naval communications system consists of a strategic group and tactical group. Strategic communications are generally worldwide and operated on a common user (Navy, Army, DOD, etc.) or special-purpose basis. A strategic system may be limited to a specified area or specific type of traffic, but its configuration is designed to permit combined operations with other strategic systems. An example is the automatic voice network and automatic digital network. Tactical communications are usually limited to a specific area of operations and are used to direct or report the movement of forces. Tactical networks may be used for operational and/or administrative traffic, e.g., task group and broadcast networks. Communication links have four basic modes of operation:
lSimplex - permits one-way communications between stations (e.g., an emergency transmitter). Communications is in one direction only. A single channel or frequency is used to exchange information between two or more terminals.
lHalf duplex - permits one-way flow of communications between terminals. Transmission may occur in either direction, but not simultaneously (e.g., a citizen's band radio). "Half duplex" must be qualified to show whether it is send only, receive only, or send/receive. A station can transmit and receive using a separate transmitter and receiver.
lDuplex - permits two-way communications simultaneously in both directions, using two separate frequencies (e.g., a telephone). Messages can be sent and received at the same time. The term "full duplex" is synonymous with "duplex".
lBroadcast - A broadcast is transmitted by one station on one or more channels directed to more than one station or unit. Broadcasts are the primary mean of delivering messages to the fleet. Broadcasts uses radiotelephone, radioteletype, and facsimile equipment.
Figure 4.1-1 shows the international electromagnetic frequency spectrum as defined by the International Telegraph Union.
3X103 3x104 3x105 3x106 3x107 3x108 3x109 3x1010 3x1011 3x1012 3x1013 3x1014 3x1015 3x1016 3x1017 3x1018 3x1019 3x10203x10213x1022
│ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │
│ │ │ │ │ │ --MICROWAVES--│ │ │ │ │ │ ---X-RAYS---│ │COSMIC-----│
│ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │RAYS │ │
│--------------COMMUNICATIONS--------------- │ │ │ VISIBLE │ │ │ │ │ │ │
│ │ │ │ │ │ │ │ │ │ │ │LIGHT│ │ │ │ │ │ │ │
│ │ │ │ │ │ │ │ │ │ │ │ --- │ │ │ --GAMMA RAYS--│ │ │
│ │ │ │ │ -------RADAR------- │ │ │ │ │ │ │ │ │ │ │ │
│ │ │ │ │ │ │ │ │ │ │ │ │ ULTRA- │ │ │ │ │ │
│ │ │ │ │ │ │ │ │ -----INFRARED---- ---VIOLET-- │ │ │ │ │ │
│ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │
│ VLF │ LF │ MF │ HF │ VHF │ UHF │ SHF │ EHF │ │ │ │ │ │ │ │ │ │ │ │
107 106 105 104 103 102 101 100 10-1 10-2 10-3 10-4 10-5 10-6 10-7 10-8 10-9 10-10 10-11 10-12
Figure 4.1-1 Frequency Spectrum
Rapid growth in the quantity and complexity of communications equipment and increased worldwide international requirements for radio frequencies placed large demands on the RF spectrum. These demands include military and civilian applications, such as communications, location and ranging, identification, standard time and frequency transmission, and industrial, medical, and other scientific uses. The military frequency spectrum as shown in Table 4.1-1. Note that the U.S. government plans to sell portions of the military frequency spectrum as of this writing.
║Frequency │Description ║
║0 Hz - 3 kHz │Extremely Low Frequency (ELF) ║
║3 kHz - 30 kHz │Very Low Frequency (VLF) ║
║30 kHz - 300 kHz │Low Frequency (LF) ║
║300 kHz - 3 MHz │Medium Frequency (MF) ║
║3 MHz - 30 MHz │High Frequency (HF) ║
║30 MHz - 300 MHz │Very High Frequency (VHF) ║
║300 MHz - 3 GHz │Ultra High Frequency (UHF) ║
║3 GHz - 30 GHz │Super High Frequency (SHF) ║
║30 GHz - 300 GHz │Extremely High Frequency (EHF)║
Table 4.1-1 Military Frequency Spectrum
FREQUENCY BAND USE
The allocation, assignment, and protection of all frequencies used by U.S. Navy components is the responsibility of Commander, Naval Telecommunications Command (COMNAVTELCOM). Frequencies and equipment are chosen to meet the communications application desired. The following paragraphs discuss the characteristics and use of the RF spectrum.
ELF Communications (0 - 3 kHz)
An ELF communications system is a one-way system, used to send short phonetic letter spelled out (PLSO) messages from operating authorities in CONUS to submarines. ELF has the ability to penetrate ocean depths to several hundred feet with little signal loss. This ability allows submarines to operate well below the immediate surface, making detection more difficult. The ELF system transmits only from shore to ship. The large size of ELF transmitters and antennas makes ELF transmission from submarines impractical.
VLF Communications (3 - 30 kHz)
The location of operating forces affects the capacity, range, and reliability of communications, particularly in the North Atlantic and Arctic Oceans. HF circuits are unreliable in these areas because of local atmospheric disturbances. VLF transmissions provide highly reliable communications in these northern latitudes. VLF transmission is normally considered a broadcast; that is, a one-way transmission, no reply required. VLF is used for communications to satellites and as a backup to shortwave communications blacked out by nuclear activity. Other applications include transmission of standard frequency and time signals, tracking space vehicles, oscillator calibration, international comparisons of atomic frequency standards, radio navigation aids, astronomy, national standardizing laboratories, and communications systems. At present, practically all Navy VLF transmitters are used for fleet communications or navigation. A VLF broadcast of standard time and frequency is sufficiently accurate for the operation of cryptographic equipment, decoding devices, and single sideband transmissions.
LF Communications (30 - 300 kHz)
The LF band has been used for communications since the advent of radio. LF transmitting installations are characterized by a large physical size and high construction and maintenance costs. Over the years, propagation factors peculiar to the LF band have resulted in their continued use for radio communications. LF waves are not seriously affected during periods of
ionospheric disturbance when communications at higher frequencies are disrupted. The use of low frequencies at latitudes near the equator is sometime limited by atmospheric noise. Because of this, the navy has a particular interest in the application of low frequencies in northern latitudes. In the past, the fleet broadcast system provided ships at sea with LF communications via CW (continuous wave) telegraph transmissions. As technology advanced, the system was converted to single-channel radio teletypewriter (RTTY) transmission. Today, LF communications are used to provide eight channels of frequency-division multiplex RTTY traffic on each transmission of the fleet multichannel broadcast system.
MF Communications (300 kHz - 3 MHz)
The MF band of the RF spectrum includes the international distress frequencies. Some ships have MF equipment and can monitor these distress frequencies. Ashore, the MF receiver and transmitter equipment is usually affiliated with coastal SAR organizations. Only the upper and lower ends of the MF band have naval use because the commercial broadcast band (AM) extends from 535 to 1605 kHz. Frequencies in the lower portion of the MF band (300 to 500 kHz) are
used primarily for ground wave transmission for moderately long distances over land. Transmission in the upper MF band is generally limited to short haul communications (400 miles or less).
HF Communications (3 MHz - 30 MHz)
The U.S. Navy began using HF for radio communications during World War I. A few communications systems were operated on frequencies near 3 MHz and used for very short range communications of a few miles. The general belief at the time was that frequencies above 1.5 MHz were useless for long range communications. Today HF is used extensively for long range communications. The military HF band has been expanded to include frequencies from 2 MHz through 32 MHz. Navy HF use currently includes Fleet Broadcast (as a satellite backup), teletype circuits, single channel voice, and Link 11. One of the prominent features of HF long distance communications is a change in signal strength due to changes in the propagation medium. HF radio waves are transmitted over long distances by being reflected by the ionosphere. The ground distance a radio wave travels and the strength it has when it gets to the receiver depend on how dense the ionosphere is and how far it is from the earth. High, dense ionosphere layers tend to produce longer and stronger signals than lower and less dense ionosphere layers.
The height and density of the ionosphere are determined primarily by ultraviolet radiation from the sun. Height and density vary significantly with time of day, season, and sunspot activity. As the height and density of the ionosphere change, the strength of the radio signal will change, sometimes fading or disappearing completely. Therefore, you must generally use more than a single frequency, sometimes up to four or five, to maintain HF communications. HF
communicators have had difficulty communicating at ranges between 20 and 300 miles, that tactically important region called the skip zone - too far for ground wave coverage and not far enough for the reflected sky wave. Conventional wisdom holds that HF has no role to play in the skip zone, but with the right antenna configuration and proper frequency selection, the skip zone can be covered with a clear, strong HF signal. See "Tactical HF Enters the Skip Zone" by LCDR Toher, Proceedings, April 1993.
In spite of the difficulties encountered with HF propagation, the economic and technical advantages of using HF led to a rapid expansion in the use of the band, resulting in near saturation. The HF spectrum is shared by many domestic and foreign users, and only portions scattered throughout the band are allocated to the military. Navy requirements for HF also grew, with the capacity of the Navy's assigned portion of the spectrum becoming severely taxed. The use of single sideband (SSB) equipment and the application of independent sideband techniques increased the capacity, but not enough to catch up with demand. Newer technologies, namely satellite communications and UHF relays and repeaters have overshadowed HF operations. Regardless, the HF spectrum most likely will continue to be in high demand for some time, due to HF system's versatility, survivability, and cost. Generally, less than optimum HF performance of shipboard equipment is partially offset by powerful transmitters and sensitive receiving systems at shore terminals. Naval communications in the HF band can be grouped as point-to-point, ship-to-shore, ground-to-air, and broadcast. All but fleet broadcast are normally operated as two way communications.
lPoint-to-Point - established to communicate over long distance trunks or links between fixed terminals. A trunk is normally a message circuit between two points that are both switching centers or individual message distribution points. A link is a transmitter-receiver system connecting two locations. Generally, terminals use large antennas aimed at the opposite terminals of the link. This increases effective power and the sensitivity of the receiving system; it also reduces susceptibility of a circuit to interference. With the path length and direction fixed, other propagation factors are simplified and highly reliable communications can be achieved.
lShip-to-Shore - This application of the HF band is more difficult than point-to-point since the ship is moving and constantly changing position. In ship-to-shore, the path length and direction are variable. Aboard ship, limited space and other restrictions prohibit installation of large, efficient HF antennas. Because of mobility, shipboard antennas are designed to be as omnidirectional as possible. These problems are not as severe at the shore terminal where there is sufficient space for efficient omnidirectional antennas or arrays designed for coverage of large areas of the earth. At shore stations, rotatable high-gain antennas or fixed point-to-point antennas are used. Several frequencies are usually assigned for each circuit. This allows the selection of a frequency that best matches the propagation path conditions between the shore terminal and the ship.
lGround-to-Air - The use of HF for ground-to-air communications is similar to ship-to-shore use. The only difference is that an aircraft moves more rapidly than a ship. All major circuit improvements must be made at the ground station. For example, high powered
lFleet Broadcasts - involves broadcast area coverage from shorebased transmitters to ships at sea. Messages to be broadcast to ships are delivered by various means to the broadcast station. To overcome propagation problems, naval communicators send their messages on
several frequencies at once. This is known as frequency diversity transmission. This type of transmission allows the ship to choose the best frequency for reception. Space diversity, with physically separated receiving antennas, also helps to overcome this problem.
VHF and Above Communications
Frequencies above 30 MHz are not normally refracted by the atmosphere and groundwave range is minimal. This normally limits our use of this frequency spectrum to line of sight (LOS). The exception is increasing range through the use of tropospheric scatter techniques. Some communications using VHF and above frequencies use a technique called forward propagation by tropospheric scatter (FPTS). Certain atmospheric and ionospheric conditions can also cause the normal LOS range to be extended. Frequencies at the lower end of this band can overcome the shielding effects of hills and structures to some degree; but as the frequency is increased, the problem becomes more pronounced. Reception is notably free from atmospheric and manmade static. (VHF and UHF bands are known as LOS transmission bands.) Because this is LOS communications, the transmitting antenna is in a direct line with the receiving antenna and not over the horizon (OTH). The LOS characteristic makes the VHF band ideal for amphibious operations and the UHF band well suited for tactical voice transmissions.
A large portion of the lower end of the VHF band is assigned to commercial television and FM radio industry and used by the Navy in amphibious operations. The upper portion of the VHF band (225 MHz to 300 MHz) and the lower portion of the UHF band (300 MHz to 400 MHz) are used extensively by the Navy for short range, aircraft, and satellite communications. The SHF band is used for missile illuminators, navigation/surface search radars, missile acquisition radars, Lamps III Data Link and satellite communications. The EHF band is used for experimental purposes and satellite communications.
RF currents flowing through a transmitting antenna produce electromagnetic waves that radiate from the antenna in a manner similar to the way waves radiate on the surface of a pond when a rock is thrown into the water. However, electromagnetic waves travel either parallel to the surface of the earth (horizontally polarized) or perpendicular to the surface of the earth (vertically polarized). These transmitted waves travel toward receiving antennas by a means known as propagation. Figure 4.1-2 identifies the divisions of the transmitted electromagnetic wave according to propagation characteristics: the groundwave, skywave, and spacewave.
The groundwave (Figure 4.1-3) is the portion of the radiated wave that moves along the surface of the earth. The field strength of the groundwave diminishes with distance much more rapidly than the waves that move through free space. Absorption by the earth increases with an increase in frequency, so long distance communications by groundwaves are limited to low frequencies at very high power. Daytime reception of the Standard Broadcast Band (AM) is an example. The type of soil near the antenna site is also a factor in attenuation of the groundwave. Clay or loam will attenuate the signal less than sand or rock. However, salt water will propagate the signal
Figure 4.1-2 Divisions of the Transmitted Electromagnetic Wave
Figure 4.1-3 Groundwave Component of the Transmitted Electromagnetic Wave
better than either type of soil. The horizontally polarized wave is short circuited by the earth and is attenuated much more rapidly than the vertically polarized wave. Thus, to gain maximum advantage, the groundwave must be transmitted and received using vertically polarized antennas. Despite these limiting factors, the groundwave remains the most reliable means of radio communications because most of the restricting factors do not vary with time of day or weather conditions.
The skywave is the portion of the electromagnetic signal radiated upward that may or may not be refracted back to earth by the ionosphere (the upper atmosphere beginning 40 to 50 miles above the earth). Figure 4-1.4 shows the skywave component during daylight hours, as refracted by the layers of the ionosphere. Skywave propagation is not as reliable as groundwave propagation however, much greater distances may be covered by skywave because the radiated electromagnetic field directed toward the ionosphere is refracted (bent and reflected) back by the denser ionosphere at distances of hundreds or even thousands of miles. The angle at which the energy is refracted depends on many variables, the major ones being the frequency and angle of the radiation, and the height and density of the ionospheric layers. There is an angle at which the electromagnetic waves that enter the ionosphere will be refracted, but not enough to return to
earth. This angle is called the critical angle. Any transmitted energy entering the ionosphere beyond this angle continues into free space.
The ionosphere differs from other atmospheric layers because it contains a much higher number of positive and negative ions. The negative ions are believed to have energy levels that have been increased greatly by solar bombardment of ultraviolet and particle radiation. Extending from about 30 miles to 250 miles in the ionosphere are four layers of ionization: D, E, F1, and F2. Although ionization appears in distinguishable layers, the intensity and height of ionized layers in any given region depend on many factors including season, sunspot cycle, and most readily apparent, the time of day. The D layer is present only during daylight and has little effect on refraction, but it is a factor in absorbing energy from the electromagnetic fields that pass through it. The E layer is much stronger during the day than at night and can refract
frequencies up to approximately 20 MHz during the daylight hours. The F layers have the most effect on the refraction of electromagnetic energy. During the night the D layer fades, the E
layer becomes much weaker, and the F1 and F2 layers combine into a single F layer. The
Figure 4.1-4 Skywave Component of the Transmitted Electromagnetic Wave
reduction in absorption losses because of the fading of the D and E layers can cause the electromagnetic energy to cover greater distances at night. Additionally the combined F1 and F2 layers refract higher energy level signals at greater angles. Figure 4.1-5 depicts a comparison of day and night ionospheric layers.
Figure 4.1-5 Layers of the Ionosphere
Long-distance radio communications may be conducted by using multi-hop transmissions. During these transmissions, a sequence of refractions in the ionosphere and reflections from the earth occur, causing the electromagnetic energy to "bounce" several times over the distance covered. The complete effects of all the variables on skywave propagation are not fully understood. Researchers are continuously searching for means to improve the reliability of long distance skywave communications.
The spacewave (Figure 4.1-6), also referred to as the direct ground wave, is the part of the total wavefront that travels directly, or is reflected by the earth from the transmitting antenna, to the receiving antenna. The spacewave is limited to LOS distances plus the additional small distance created as atmospheric diffraction bends the wave a slight amount around the curvature of the earth. Naturally, LOS distance can be increased by increasing either one or both of the heights of the transmitting and receiving antennas and by using a repeater.
The reflected spacewave is bounced off of the earth at some distance between the transmitting and receiving antennas. When the transmitted wave strikes the surface of the earth, a part of the energy is lost in the form of heat dissipation. The balance is reflected at the same angle at which it arrived. When the wave is reflected from the surface of the earth, it undergoes a phase reversal of 180° (See insert, Figure 4.1-6). Also, since the reflected wave travels a somewhat longer distance than the LOS spacewave, it arrives at the point of reception later than the LOS
spacewave. These two factors are important because the 180° phase shift plus the longer route
Figure 4.1-6 Spacewave Component of the Transmitted Electromagnetic Wave
may cause the reflected wave to be out of phase with the LOS wave at the point of reception. In other words, the two waves may have a tendency to cancel each other at the receiving antenna.
ATMOSPHERIC EFFECTS ON PROPAGATION
Variations in the earth's atmosphere have a direct effect on wave propagation. The factor that has the greatest effect on radio communications is absorption. Absorption decreases the energy of a radio wave and has a pronounced effect on both the strength of received signals and the ability to communicate over long distances.
The most troublesome and frustrating problem in receiving radio signals is variations in signal strength, most commonly known as fading. There are several conditions that can produce fading.
When a radio wave is refracted by the ionosphere or reflected from the earth's surface, random changes in the wave's polarization may occur. This change in polarization may adversely affect reception, depending on the polarization of the receiving antenna. An antenna, depending on how it is designed and mounted, will receive either vertically polarized or horizontally polarized signals at full strength, but not both. If an antenna meant to receive vertically polarized signals receives a horizontally polarized signal, or vice versa, it will pass only a small portion of the signal to the receiver. This decrease in signal passed to the receiver will be indicated by a decrease in receiver output. At the lower frequencies, wave polarization will remain fairly constant as it travels through space. At higher frequencies polarization usually varies, sometimes
quite rapidly, because the wavefront splits into several components which follow different paths. Fading also results from absorption of RF energy in the ionosphere. Absorption fading occurs for a longer period of time than other types of fading since absorption takes place slowly. For the most part however, fading on ionospheric circuits is mainly a result of multipath propagation.
Multipath fading is the propagation of identical signals via separate paths to a particular location. Multipath fading results from the multiple paths a radio wave may follow between a transmitter and receiver. Propagation paths include the ground wave, ionospheric refraction, re-radiation by the ionospheric layers, and reflection from the earth's surface or from more than one ionospheric layer. Multipath fading may be minimized by practices called space diversity and frequency diversity. In space diversity, two or more receiving antennas are spaced some distance apart. Fading does not occur at the same time at both antennas; therefore, sufficient output is almost
always available from one of the antennas to provide a useful signal. In frequency diversity, two transmitters and two receivers are used, each pair tuned to a different frequency, with the same information being transmitted at the same time over both frequencies. One of the two receivers will almost always provide a useful signal.
Fading resulting from multipath propagation varies with frequency since signals of different frequencies arrive at the receiving point via a different radio paths. When a wide band of frequencies is transmitted at the same time, each frequency will vary in the amount of fading. This variation is called selective fading. When selective fading occurs, all frequencies of the
transmitted signal do not retain their original phases and relative amplitudes. This fading causes severe distortion of the signal and limits the total signal transmitted.
All radio waves propagated over ionospheric paths undergo energy losses on their way to the receiving site. As discussed earlier, absorption in the ionosphere and lower atmospheric levels account for a large part of these energy losses. There are two other types of losses that also significantly affect the ionospheric propagation of radio waves. These losses are known as ground reflection loss and freespace loss. The combined effects of absorption, ground reflection loss, and freespace loss account for almost all the energy losses of radio transmissions propagated by the ionosphere.
VARIATIONS IN THE IONOSPHERE
Because the existence of the ionosphere is directly related to radiations from the sun, the earth's orbit around the sun, solar flares and sunspots create variations in the ionosphere. These variations are of two general types: those that are more or less regular and occur in cycles and those that are irregular. Regular variations can be predicted and planned for, whereas irregular variations cannot. Both significantly effect propagation.
The regular variations that affect the extent of ionization in the ionosphere can be divided into four main classes: daily, seasonal, 11-year, and 27-day variations.
lDaily - Daily variations in the ionosphere result from the 24-hour rotation of the earth about its axis.
lSeasonal - Seasonal variations result from the earth revolving around the sun. The relative position of the sun moves from one hemisphere to the other with changes in seasons. Seasonal variations of the D, E, and F1 layers correspond to the highest angle of the sun. Ionization density of these layers is greatest during the summer. The F2 layer however, does not follow this pattern. F2 ionization is greatest in winter and least in summer. Consequently, operating frequencies for F2 layer propagation are higher in the winter than summer.
lEleven Year Sunspot Cycle - One of the most notable solar phenomena is the appearance and disappearance of dark, irregularly shaped areas known as sunspots. Scientists believe that sunspots are caused by violent eruptions on the sun and are characterized by unusually strong magnetic fields. Sunspots cause variations in the ionization level of the ionosphere. Sunspots can occur unexpectedly and the lifespan of individual sunspots is variable. However, a regular cycle of sunspot activity has been observed. This cycle has both a minimum and maximum level of activity occurring approximately every 11 years. During periods of maximum activity, the ionization density of all layers increases. Because of this, absorption in the D layer increases and the critical frequencies for the E, F1 and F2 layers
are higher. At these times, higher operating frequencies must be used for long distance communications.
lTwenty Seven Day Sunspot Cycle - This sunspot cycle causes variations in the ionization density of the layers at 27-day intervals. This cycle corresponds to the approximate time that it takes the sun to complete one rotation. It causes variations in the ionization density on a day to day basis and causes fluctuations in the F2 layer, more so than for any other layer. For this reason, precise predictions of the day to day critical frequency of the F2 layer are not possible. In calculating frequencies for long distance communications, allowances for the fluctuations of the F2 layer must be made.
Irregular variations in ionospheric conditions also effect propagation. Because these variations are irregular and unpredictable, they can drastically affect communication capabilities without
warning. The more common irregular variations are sporadic E, sudden ionospheric disturbances, and ionospheric storms.
lSporadic E - Irregular cloudlike patches of unusually high ionization, called sporadic E, often form at heights near the normal E layer. Exactly what causes this phenomenon is not known, nor can its occurrence be predicted. It is known to vary significantly with latitude. In the northern latitudes, it appears to be closely related to the aurora or polar lights.
lSudden Ionospheric Disturbance - This is the most startling of the ionospheric irregularities. These disturbances may occur without warning and may prevail for any length of time, from a few minutes to several hours. When SID occurs, long distance propagation of HF radio waves is almost totally blanked out. The immediate effect is that radio operators listening on normal frequencies are inclined to believe their receivers have failed.
lIonospheric Storms - Ionospheric storms are disturbances in the earth's magnetic field. They are associated, in a manner not fully understood, with both solar eruptions and the 27 day intervals, thus corresponding to the rotation of the sun.
Scintillation refers to the phenomenon that causes the disturbance of RF signals as they pass through the ionosphere. Although there is much to be learned about ionospheric scintillation, observations indicate that it occurs within approximately 20° of the equator, and in polar regions
within the auroral zones. The effects are most pronounced between the hours of ionospheric sunset and sunrise (or approximately 2200 to 0600 local time on the earth's surface). Records indicate scintillation is most severe near the vertical and autumnal equinoxes and at a minimum near the summer and winter solstices. The effect of scintillation on RF signals decreases as the frequency increases. Consequently, while scintillation may disrupt UHF satellite communications in a specific area, the effect on SHF satellite communications is negligible. Scintillation is caused by the same factors that make stars appear to twinkle, i.e., irregularities in the electron density of the ionosphere. During daylight hours, solar energy maintains a reasonably level degree of ionization (i.e., a stable level of Total Electron Count or TEC). At ionospheric sunset, removal of the sun's energy results in a rapid decrease in the TEC. Ions and electrons recombine, causing release of excess energy. This excess energy is absorbed and ionization occurs. This process continues until energy from the sun again establishes a stable TEC, around ionospheric sunrise.
Weather is an additional factor that affects the propagation of radio waves. In this section, we explain how and to what extent various weather phenomena affect wave propagation. Wind, air temperature, and water content of the atmosphere can combine in many ways. Certain combinations can cause signals to be heard hundreds of miles beyond the ordinary range of radio communications. Conversely, a different combination can attenuate the signal to the extent that it may not be heard even over a normally satisfactory path. Unfortunately, there are no hard and fast rules concerning the effects of weather on radio transmissions since weather is extremely
complex and subject to frequent change. Therefore, the following discussion of the effects of weather on radio waves is limited to general terms.
Calculating the effect of weather on radio wave propagation would be comparatively simple if
there were neither water nor water vapor in the atmosphere. However, water in vapor, liquid, or
solid form is always present and must be considered in all calculations. Before we discuss the specific effects that several forms of precipitation (rain, snow, fog) have on radio waves, you
should note that the attenuation effects of precipitation are generally proportionate to the frequency and wavelength of the radio wave. For example, rain has a pronounced effect on microwave frequencies. You can assume then, that as the wavelength becomes smaller with increases in frequency, precipitation causes a greater attenuation of the radio waves. Conversely, you can assume that as the frequency is reduced and the wavelength increased, precipitation has little effect on radio waves in the HF range and below.
Attenuation caused by rain is greater than attenuation due to other forms of precipitation. Attenuation may be caused by absorption and scattering. A raindrop, acting as a poor dielectric, absorbs power from the radio wave and dissipates the power in the form of heat loss. At frequencies above 100 MHz raindrops cause greater attenuation by scattering than by absorption. At frequencies above 6 GHz, attenuation by raindrop scatter is even greater.
The amount of attenuation is determined by the quantity of water per unit volume and by the size of the droplets. Attenuation due to fog is of minor importance at frequencies lower than 2 GHz. However, above 2 GHz fog can cause serious attenuation by absorption.
Scattering caused by snow is difficult to compute because of the irregular sizes and shapes of snowflakes. Scientists assume that attenuation from snow is less than that from rain falling at an equal rate because the density of the rain is eight times that of snow. In other words, rain falling one inch per hour would have more water per cubic inch than snow falling at the same rate.
Attenuation by hail is determined by the size of the stones and their density. Attenuation of radio waves by scattering because of hailstones is considerably less than by rain.
We have discussed uncontrollable factors that effect propagation. Selection of transmitting and
receiving antennas and operating frequency are controllable factors. For successful communications between any two specified locations at any given time of the day, there is a maximum frequency, lowest frequency, and optimum frequency that can be used.
Maximum Usable Frequency (MUF)
As discussed earlier, higher frequency radio waves are refracted (and reflected) less by ionized layers of the atmosphere than are lower frequency radio waves. Therefore, for a given angle of
incidence and time of day, there is a maximum frequency that can be used for communications between given locations. This frequency is known as the maximum usable frequency (MUF). Frequencies above MUF are normally refracted so slowly that they return to earth beyond the desired location, or pass on through the ionosphere and are lost. You should understand, however, that use of an established MUF certainly does not guarantee successful communications. Variations in the ionosphere may occur at any time and consequently raise or lower the predetermined MUF. This is particularly true for radio waves being refracted by the highly variable F2 layer. The MUF is highest around noon when ultraviolet light waves from the sun are the most intense. It then drops rather sharply as recombination of ionospheric layers begins to take place.
Lowest Usable Frequency (LUF)
The minimum operating frequency that can be used for communications between two points is referred to as the lowest usable frequency (LUF). As the frequency of a radio wave is lowered,
the rate of refraction increases. Consequently, a wave whose frequency is below the established LUF is refracted back to earth at a shorter distance than desired. The transmission path that results from the rate of refraction is not the only factor that determines the LUF. As a frequency is lowered, absorption of the radio wave increases. A frequency that is too low is absorbed to such an extent that it is too weak for reception. Likewise, atmospheric noise is greater at lower frequencies; thus, a low frequency radio wave may have an unacceptable signal-to-noise ratio. In other words, the amplitude of noise may obscure the signal, thereby decreasing receiver sensitivity, i.e., the receiver's ability to reproduce weak signals. For a given angle of incidence
and set of ionospheric conditions, the LUF for successful communications depends on the refraction properties of the ionosphere, absorption considerations and the amount of atmospheric noise present.
Optimum Usable Frequency
Neither the MUF nor the LUF is a practical operating frequency. While the LUF can be refracted back to earth at the desired location, the signal-to-noise ratio is still much lower than at the higher frequencies and the probability of multipath propagation is much greater. Operating at or near the MUF can result in frequent signal fading and dropouts when ionospheric variations alter the length of the transmission path. A practical operating frequency is one that is high enough to avoid the problems of multipath, absorption and noise encountered at the lower frequencies; but not so high as to experience the adverse effects of rapid changes in the
ionosphere. A frequency that meets the above criteria is known as the FOT from the French "frequency optimum de travail". The FOT is roughly 85% of the MUF and varies considerably.
COMMUNICATIONS EQUIPMENT FUNDAMENTALS
Communications equipment can be divided into three broad categories: transmitting equipment, receiving equipment, and terminal equipment. Transmitting equipment generates, amplifies, and modulates a signal. Receiving equipment receives the signal, then amplifies and demodulates it to extract the original intelligence. Terminal equipment is used primarily to convert audio signals
or data into the original intelligence. A basic radio communication system consists of a transmitter and a receiver connected by electromagnetic waves (Figure 4.1-7).
Figure 4.1-7 Basic Radio Communication System
The transmitting equipment creates a radio frequency (RF) carrier and modulates it with audio intelligence to produce an RF signal. This RF signal is amplified and fed to the transmitting antenna, which converts it to electromagnetic energy for propagation. The receiving antenna
converts the transmitted electromagnetic energy into alternating RF currents. The receiver then
converts this signal back into audio intelligence.
Although there are many communications antenna designs used in U.S. Navy applications, all of these antennas have common characteristics. In this section, we will discuss antenna types and terminology.
Whenever RF current flows through a transmitting antenna, electromagnetic (radio) waves are radiated from the antenna in all directions. These waves travel at approximately the speed of light. The frequency of the radio wave that is radiated by the antenna will be the same as the frequency of the RF current flowing through the antenna. The velocity of a radio wave remains the same regardless of frequency. This is important to remember in computations that concern antenna length. When referring to the length of an antenna, the term wavelength is used. You will hear antennas referred to as halfwave, quarterwave, and fullwave. These terms describe the relative length, electrical or physical, of an antenna.
Simply stated, wavelength is defined as "the distance traveled by the radio wave in the time required for one cycle." This means that wavelength is inversely proportional to frequency. The electrical length of an antenna is not necessarily the same as its physical length. Radio frequency energy travels at the speed of light in free space however, it travels at a much slower speed in an antenna. The difference in velocity results in a difference between electrical and physical lengths. Thus, an antenna may be called a halfwave antenna because its electrical length is a halfwave, but its physical length may be much shorter. Antennas are tuned by electrically lengthening or shortening their wavelength to achieve resonance at a particular frequency.
The orientation of an antenna in space determines the polarization of the emitted radio wave. An antenna that is oriented vertically with respect to the earth radiates a vertically polarized radio wave, while a horizontally oriented antenna radiates a horizontally polarized wave. Polarization of a radio wave is a major consideration in efficient transmission and reception of radio signals. For example, if a single-wire antenna is used to extract energy from a passing radio wave, it will extract the most energy (maximum signal) when it lies physically in the same direction as the electric field component. In theory, a vertical antenna should be used for efficient reception of vertically polarized waves. A horizontal antenna should be used for reception of horizontally polarized waves. For this reason, shipboard antennas are installed with correct polarization in mind. If antennas are relocated, ensure that correct polarization is maintained.
In general, we use three terms to describe the direction or directions in which an antenna can transmit or receive: omnidirectional, bidirectional, and unidirectional. Omnidirectional antennas
radiate and receive equally well in all directions, except from their ends. Bidirectional antennas radiate or receive efficiently in only two directions: for example north/south or east/west. Unidirectional antennas radiate or receive efficiently in one direction only. Most antennas are either omnidirectional or unidirectional. Bidirectional antennas are rarely used in naval communications. Examples of an omnidirectional antenna are the antennas used to transmit fleet broadcasts or most medium-to-high frequency antennas used aboard ship. An example of a unidirectional antenna is a parabolic antenna or "dish".
A wire antenna consists of a wire rope suspended either vertically or horizontally from a yardarm or mast to outriggers, another mast, or to the superstructure. A simplified diagram of a shipboard wire antenna is shown in Figure 4.1-8. Single wire antennas are not used aboard ship as extensively now as they were in the past. They have, to a large extent, been replaced by whip, dipole, and other antenna assemblies. In some installations, wire antennas are used only in emergencies. Because of the frequency range in which these antennas are used, the portion of the ship's structure used to support the wire and other nearby structures are an electrically
Figure 4.1-8 Wire Rope Antenna
integral part of the wire antenna. Therefore, wire antennas are usually designed for a particular ship or installation. A transmitting and receiving wire rope antenna will have a vinyl insulating jacket (as will transceiving wire antennas) to reduce interference from precipitation static (static interference due to the discharge of large charges built up by rain, sleet, snow, or electrically charged clouds).
Whip antennas are essentially self-supporting. They can be installed in locations where space is at a premium or locations that are unsuitable for other antenna types. They may be deck mounted or mounted on brackets on the stacks or superstructure. Whip antennas that are used for receive only are mounted as far away from the transmitting antennas as possible to minimize the amount of energy they can pick up from a local transmitter. You can distinguish receiving whip antennas from transmitting antennas by the color of the base. Receive antennas have blue bases. Transmit antennas have red bases. A common whip antenna is constructed with 7-foot sections of aluminum rod. The lower rod is three inches in diameter and the whip tapers to a diameter of
one inch at the upper section. (Fiberglass whips are replacing the aluminum whips in some
installations.) Some whips may be trussed with wire rope (which increases the frequency bandwidth), resulting in better performance (Figure 4-1.9).
Figure 4.1-9 Trussed Whip Antenna
Whip antennas over 35 feet long are mounted on a plate supported by three or four insulators for greater strength. Small whip antennas have been mounted horizontally on yardarms or masts in some installations for use as low frequency probe antennas. Such antennas usually come supplied with a line termination box, which is normally mounted to the ship's structure. Some applications use two whips connected as a single antenna for better electrical performance. If the
antennas are less than 25 feet apart, they are usually connected with a crossbar (Figure 4.1-10), which has the feedpoint at its center. If the antennas are a considerable distance apart, or for some other reason, a direct connection is not practical, transmission line termination is used. Wire rope is used in place of the whips in some installations. On aircraft carriers and missile ships, antennas are tilted on a trunnion when installed along the edges of the flight deck or in the missile firing zone. The tilting mounts may be mechanically or hydraulically operated. Mechanically operated mounts have a counterweight at the base of the antenna heavy enough to balance the antenna in almost any position. The antenna may be locked in either a vertical or horizontal position by positive locking devices in both the operating and stowed positions.
Figure 4.1-10 Twin Whip Antennas with Crossbar Terminations
Broadband antennas for use in the HF and UHF bands have been developed for use with antenna multicouplers. To be used with a multicoupler, the antenna must be capable of handling simultaneous transmissions from several transmitters without excessive loss of power in the multicoupler equipment. The antenna must, therefore, function satisfactorily over a relatively
wide band of frequencies. The effectiveness of a given antenna depends largely on impedance matching. If a good impedance match exists between the transmission line and the antenna
throughout the operating band of frequencies, efficiency and power transfer are improved. One type of broadband antenna, called a fan, is shown in Figure 4.1-11.
Figure 4.1-11 Five-Wire Vertical Fan Antenna
Effectively, this is a V-shaped plane radiator. Physically, it is composed of five wires cut for one-quarter wavelength at the lowest frequency to be used. The wires are fanned approximately 30° between adjacent wires. On small ships, the fan antenna may consist of only three or four wires. Ships may have two fan antennas, one vertical fan and the other horizontal.
A large variety of UHF antennas have been developed for shipboard use. Two of these antennas, the AT-150/SRC and AS-390/SRC, are shown in Figure 4.1-12. They are used for transmitting or receiving vertically polarized waves in the 220 MHz and 400 MHz range.
Figure 4.1-12 UHF Antennas
An antenna matching network consists of one or more parts (such as coils, capacitors, and lengths of transmission line) connected to the transmission line at its feed point to make the antenna resonate at the applied frequency. Matching networks ensure maximum transfer of RF energy with minimum power loss. Matching networks are usually adjusted when they are installed and require no further adjustment for proper operation. Matching networks can also be built with variable components enabling one antenna to transmit a range or band of frequencies. These networks are antenna tuners or couplers. These are adjusted automatically or manually each time the operating frequency is changed.
Antenna tuning is accomplished by using matching networks in tuners, antenna couplers, and multicouplers. Antenna couplers and tuners are used to match a single transmitter or receiver to one antenna. Antenna multicouplers are used to match more than one transmitter or receiver to one antenna for simultaneous operation. There is one antenna that is perfect for radiating at every discrete frequency. At a specific frequency, all of the power being transmitted from the transmitter to the antenna will be radiated into space. Unfortunately, this is the ideal and not the rule. Normally, some power is lost between the transmitter and the antenna. This power loss is the result of the antenna not having the perfect dimensions and size to radiate perfectly all of the power delivered to it from the transmitter. Naturally, it would be unrealistic to carry a separate antenna for every frequency that a communications center is capable of radiating; a ship would require many antennas. To overcome this problem, we use antenna tuners/couplers to electrically lengthen and shorten antennas to match the frequency we want to transmit. The coupler is electrically connected to the antenna and is used to adjust the apparent physical length of the antenna by electrical means. This simply means that the antenna does not physically change length; instead, the antenna is electrically adapted, using matching networks, to the output frequency of the transmitter and "appears" to change its physical length.
Antenna Coupler Group AN/URA-38
Antenna Coupler Group AN/URA-38 is an automatic antenna tuning system intended primarily for use with the AN/URT-23(V) HF transmitter. The equipment also includes provisions for manual and semiautomatic tuning, making the system readily adaptable for use with other transmitters. The manual tuning feature is useful when a failure occurs in the automatic tuning circuits. Tuning can also be done without the use of RF power (silent tuning). This method is useful in installations where radio silence must be maintained except for brief transmission periods. The antenna coupler matches the impedance of a 15, 25, 28, or 35-foot whip antenna to the transmission line, in the 2 to 30 MHz range. When the coupler is used with the
AN/URT-23(V), control signals from the associated antenna coupler control unit automatically
tune the coupler's matching network in less than five seconds. During manual and silent
operation, the operator uses the controls mounted on the antenna coupler control unit to tune the antenna. A low power (not to exceed 250 watts) CW signal is required for tuning. Once tuned, the CU-938A/URA-38 is capable of handling 1,000 watts of peak power.
Antenna Coupler Groups AN/SRA-56, 57, and 58
Antenna Coupler Groups AN/SRA-56, 57, and 58 are designed primarily for shipboard use. Each coupler group permits several transmitters to operate simultaneously into a single, associated, broadband antenna, reducing the number of antennas required. These antenna coupler
groups provide a coupling path between each transmitter and associated antenna. They also
provide isolation between transmitters, matching networks, and tunable bandpass filters that allow only the desired band or range of frequencies to pass through the coupler. The three antenna coupler groups (AN/SRA-56, 57, 58) are similar in appearance and function, but they differ in frequency ranges. Antenna Coupler Group AN/SRA-56 operates in the frequency range from 2 to 6 MHz. The AN/SRA-57 operates from 4 to 12 MHz. The AN/SRA-58 operates in the 10 to 30 MHz range. When more than one coupler is used in the same frequency range, a 15% frequency separation must be maintained to avoid any interference.
Antenna Coupler Group AN/SRA-33
Antenna coupler group AN/SRA-33 operates in the UHF (225-400 MHz) frequency range. It provides isolation between as many as four transmitter and receiver combinations operating simultaneously into a common UHF antenna without degrading operation. The AN/SRA-33 is designed for operation with shipboard radio sets AN/SRC-20, AN/SRC-21, and AN/WSC-3.
The OA-9123/SRC multicoupler enables up to four UHF transceivers, transmitters, or receivers to operate on a common antenna. The multicoupler is compatible with the channel select control signals from AN/WSC-3(V) radio sets (except (V)1). It is also compatible with AN/SRC-20/21 radio sets (only in LOCAL mode). The unit is self-contained and is configured to fit into a standard 19-inch open equipment rack. The OA-9123/SRC consists of a cabinet assembly, control power supply assembly and four identical filter assemblies. This multicoupler is a replacement for the AN/SRA-33 and requires about one half the space.
Receive Multicoupler AN\SRA-12
The AN/SRA-12 filter assembly multicoupler provides seven radio frequency channels in the frequency range from 14 kHz to 32 MHz. Any of these channels may be used independently of the other channels, or they may operate simultaneously. Connections to the receiver are made by use of coaxial patch cords, which are short lengths of cable with a plug attached to each end.
Antenna Coupler Groups
The AN/SRA-38, AN/SRA-39, AN/SRA-40, AN/SRA-49, AN/SRA-49A, and AN/SRA-50 coupler groups are designed to connect up to 20 MF and HF receivers to a single antenna, with a highly selective degree of frequency isolation. Each of the six coupler groups consists of 14 to 20 individual antenna couplers and a single-power supply module, all slide-mounted in an equipment rack. Dummy loads take the place of antennas for the purpose of testing and troubleshooting without radiating. Additionally, there are provisions for patching the outputs from the various antenna couplers to external receivers.
Receive Antenna Distribution
Receiving antenna distribution systems operate at low power levels and are designed to prevent multiple signals from being received. The basic distribution system has several antenna transmission lines and several receivers. The system includes two basic patch panels, one that terminates the antenna transmission lines and the other that terminates the lines leading to the receivers. Thus any antenna can be patched to any receiver via patch cords. Some distribution systems will be more complex i.e., four antennas can be patched to four receivers, or one antenna can be patched to more than one receiver via the multicouplers.
Your voice, viewed electronically, is a waveform in the audio frequency range. The audio frequency range in radiotelephone circuits is quite low, approximately 250 - 3000 Hz. It is not practical to transmit audio frequencies into space because circuit components and antennas would be too large. Consequently, audio signals are impressed on an RF signal in a process called modulation. This RF signal is called a carrier. The audio signal is called the modulating signal. The amplitude or frequency of the carrier signal is varied by the modulating signal. When the
demodulating and carrier signals are combined they produce a complex wave. The complex wave is transmitted and received by the use of antennas. When the complex wave is received by an antenna it must be demodulated to reproduce the component carrier and modulating signal. Therefore, demodulation permits recovery of the audio signal.
A simple analogy of this process is a conversation between two people at a distance. If a person in Newport wants to talk to someone in Washington, DC, simply going outside and yelling while facing south will not work. The voice in Newport must be amplified and carried in some way to Washington. In radio communications voice is carried by a radio signal through the process of
modulation. When this radio signal is received in Washington, it cannot be heard by the human
ear until the voice has been extracted from the carrier by the process of demodulation.
Amplitude modulation (AM) is the process of combining audio frequency and radio frequency signals in a manner that causes the amplitude of the radio frequency waves to vary at an audio frequency rate.
Frequency modulation (FM) is the process of combining audio and carrier signals in a manner that causes the frequency of the carrier wave to vary at an audio rate, while the amplitude of the carrier wave remains essentially constant. The carrier frequency can be varied a small amount on
either side of its average or assigned frequency by means of the audio frequency (AF) modulating signal. The amplitude of the audio modulating signal determines the amount of change (increase) in the frequency of the FM signal. The greater the audio signal amplitude (i.e., the louder the sound in voice modulation), the greater the increase in frequency of the FM signal).
The number of communications networks in operation at any given time is constantly increasing. As a result, all areas of the RF spectrum have become highly congested. To a great extent, the maximum permissible number of intelligible transmissions taking place in the radio spectrum per unit of time is being increased through the use of multiplexing. Multiplexing involves the simultaneous transmission of a number of intelligible signals using only a single transmitting path. Two methods of multiplexing, time division and frequency division multiplexing, are widely used in U.S. Naval communications.
A transmitter may be a simple, low power (milliwatts) unit for sending voice messages a short distance, or it may be a highly sophisticated unit using thousands of watts of power, for sending many channels of data (voice, teletype, TV, telemetry, etc.) simultaneously over long distances. Basic transmitters are discussed in the following section.
The CW transmitter is turned on and off (keyed) to produce long or short radio frequency (RF) pulses that correspond to the dots and dashes of the Morse code characters. The transmitter (Figure 4.1-13) has four essential components:
lRF Generator - produces an RF signal
lRF Amplifier/Multiplier - provides a means of amplifying and, if necessary, multiplying the frequency of the RF signal
lKeyer - provides a method of turning the transmitter on and off according to the code to be transmitted
lPower Supply - provides operating voltages to electron tubes and transistors.
lAlthough not physically a part of the transmitter, an antenna is required to radiate the keyed output RF signal of the transmitter.
CW is one of the oldest and least complicated forms of radio communications. Two advantages of CW transmission are a narrow bandwidth, which requires less power out, and a degree of
intelligibility that is high even under severe noise conditions. A major disadvantage is that the
CW transmitter must be manually turned on and off at specified intervals to produce Morse code
keying. This method of transmitting intelligence is very slow and inefficient by current standards. Therefore, the navy relies on modulation of the carrier frequency (RF output of the transmitter) for communications.
Figure 4.1-13 Continuous Wave Transmitter Block Diagram
Figure 4.1-14, a block diagram of an AM transmitter, gives you an idea of what a simple AM transmitter looks like. The oscillator produces an RF carrier that is amplified and modulated with an audio signal for transmission. A microphone converts the audio frequency input (voice)
into electrical energy. The driver amplifies the audio, and the modulator further amplifies the audio signal to the amplitude necessary to modulate the carrier. The output of the modulator is applied to the power amplifier (PA). The PA combines the RF carrier and the modulating signal
to produce the amplitude modulated signal output for transmission. In the absence of a modulating signal, a continuous RF carrier is radiated by the antenna. The waveform at the antenna contains three major frequencies: the carrier frequency, the carrier frequency plus the audio frequency (sum frequency), and the carrier frequency minus the audio frequency (difference frequency). The sum frequency is called the upper sideband; the difference frequency, the lower sideband. The sideband frequencies are always related to the carrier frequency by the sum and difference of the modulation frequency. During modulation, the peak voltages and currents on the RF power amplifier stage are greater than those that occur when the stage is not modulated. To prevent damage to the equipment, a transmitter, designed to transmit both CW and radiotelephone signals, is provided with controls that reduce the power output for radiotelephone operation.
Figure 4.1-14 AM Radiotelephone Transmitter Block Diagram
Figure 4.1-15 is a block diagram of a frequency modulated transmitter. With no modulation, the oscillator generates a steady center frequency. With modulation applied, the output of the modulator is varied around the center frequency according to the modulating signal. The amount of variation from the carrier frequency depends on the magnitude of the modulating signal and the rate of variation in carrier frequency depends on the frequency of the modulating signal. The oscillator output is then fed to a frequency multiplier to increase the frequency and then to a power amplifier to increase the amplitude to the desired level for transmission.
Frequency modulation and phase modulation are essentially the same. The primary difference is in the physical method of making the frequency shift in the transmitter. Both FM and PM can be received on FM receivers, and both are commonly referred to as FM. In PM, frequency modulation is achieved by a phase shift system. The transmitter oscillator is maintained at a constant frequency by a quartz crystal. The constant oscillator output, or carrier, is amplified and modulated in a carrier phase shift network in a manner that causes the frequency of the carrier to shift according to the variations of the audio signal. The FM output of the phase shift network is fed into a series of frequency multipliers that raise the signal to the desired output frequency. Then the signal is amplified in the power amplifier and coupled to the antenna for radiation.
Figure 4.1-15 FM Transmitter Block Diagram
SINGLE SIDEBAND TRANSMITTER
A carrier that has been modulated by voice or music is accompanied by two identical sidebands, each carrying the same intelligence. In AM transmitters, the carrier and both sidebands are transmitted. In a single sideband (SSB) transmitter, only one of the sidebands, the upper or lower, is transmitted, while the remaining sideband and the carrier are suppressed, eliminating the undesired portions of the signal.
There are several advantages to SSB communications. When the carrier and one sideband are eliminated, less power is required to transmit the signal. Also, an SSB signal occupies a smaller portion of the frequency spectrum. This results in two advantages, narrower receiver bandpass and the ability to place more signals in a small portion of the frequency spectrum. SSB communication systems have some disadvantages. The process of producing an SSB signal is somewhat more complicated than simple amplitude modulation, and frequency stability is much more critical in SSB communication. While there is not the annoyance of heterodyning from adjacent signals, a weak SSB signal may be completely masked or hidden from the receiving station by a stronger signal. Also, a carrier of proper frequency and amplitude must be reinserted at the receiver because of the direct relationship between the carrier and the sidebands.
Figure 4.1-16 is a block diagram of a SSB transmitter. The audio amplifier increases the amplitude of the incoming signal to a level adequate to operate the SSB generator. The SSB generator (modulator) combines its audio input and its carrier input to produce the two sidebands. The two sidebands are then fed to a filter that selects the desired sideband and suppresses the
other one. In most cases SSB generators operate at very low frequencies compared to the normally transmitted frequencies. For that reason, we must convert (or translate) the filter output to the desired frequency. This is the purpose of the mixer stage. A second output is obtained from the frequency generator and fed to a frequency multiplier to obtain a higher carrier frequency for the mixer stage. The output from the mixer is fed to a linear power amplifier to increase the level of the signal for transmission.
Figure 4.1-16 SSB Transmitter Block Diagram
In SSB the carrier is suppressed (or eliminated) at the transmitter and the sideband frequencies produced by the carrier are reduced to a minimum. You will probably find this reduction (or elimination) is the most difficult aspect in the understanding of SSB. In a SSB suppressed
carrier, no carrier is present in the transmitted signal. It is eliminated after the signal is modulated and is reinserted at the receiver during the demodulation process. All RF energy appearing at the transmitter output is concentrated in one sideband. After the carrier is eliminated, the upper and lower sidebands remain. If one of the two sidebands is filtered out before it reaches the power amplifier stage of the transmitter, the same intelligence can be transmitted on the remaining sideband. All power is then transmitted in one sideband, instead of being divided between the carrier and both sidebands, as it is in conventional AM.
A receiver processes modulated signals received by its antenna and reproduces the original signal that modulated the RF carrier at the transmitter. The signal can then be applied to a terminal
device such as a loudspeaker or a teletypewriter.
Whatever its degree of sophistication, a receiver must perform the following basic functions: reception, selection, detection, and reproduction. Reception occurs when a transmitted electromagnetic wave passes through the receiver antenna and induces a voltage in the antenna. Selection is the ability to select a particular station's frequency from all other station frequencies appearing at the receiver's antenna. Detection is the action of separating the low (audio) frequency intelligence from the high (radio) frequency carrier and is done in a detector circuit.
Reproduction is the action of converting the electrical signals to sound waves that can then be interpreted by the ear as speech.
Receiver characteristics are useful in determining operational conditions and for comparing one receiver to another. Important receiver characteristics are sensitivity, noise, selectivity, and fidelity.
Sensitivity is a measure of a receiver's ability to reproduce very weak signals. The weaker the signal that can be applied to a receiver and still produce a certain value of signal output, the better that receiver's sensitivity. Receiver sensitivity is measured under standardized conditions and expressed in terms of signal voltage, usually in the microvolts that must be applied to the antenna input terminals to give a particular output level. The output may be an AC or DC voltage measured at the detector output or a power measurement at the loudspeaker or headphones.
All receivers generate a certain amount of noise that must be taken into account. Noise is a limiting factor on the minimum usable signal that the receiver can process and still deliver a
usable output. Therefore, the measurement is made by determining the amplitude of the signal at the receiver input required to give a signal plus noise output at a predetermined ratio above the static noise output of the receiver (signal-to-noise ratio).
Selectivity is the degree of distinction made by the receiver between the desired signal and unwanted signals. The better the receiver's ability to exclude unwanted signals, the better its selectivity. The degree of selectivity is determined by the sharpness of resonance to which the frequency determining circuits have been engineered and tuned. Measurement of selectivity is usually by a series of sensitivity readings in which the input signal is stepped along a band of frequencies above and below resonance of the receiver's circuit (e.g., 100 kHz below to 100 kHz
above tuned frequency). As the frequency to which the receiver is tuned is approached, the input level required to maintain a given output level will fall. As the tuned frequency is passed, the
required input level will rise. Input voltage levels are then plotted against frequency. The steepness of the curve at the tuned frequency indicates the selectivity of the receiver.
The fidelity of a receiver is its ability to accurately reproduce the signal that appears at its input. In general, the broader the band passed by frequency selection circuits, the greater the fidelity. Fidelity may be measured by modulating an input frequency with a series of audio frequencies, then plotting the output measurements at each step against the audio input frequencies. The resulting curve will show the limits of reproduction. Good selectivity requires that a receiver pass a narrow frequency band. Good fidelity, on the other hand, requires that the receiver pass a broader band to amplify the outermost frequencies of the sidebands. Therefore, receiver design is generally a compromise between good selectivity and high fidelity.
AM SUPERHETERODYNE RECEIVER
Figure 4.1-17 shows a block diagram with waveforms of a typical AM superheterodyne receiver. The RF carrier comes in from the antenna and is applied to the RF amplifier. The output of the amplifier is sent to the mixer. The mixer also receives an input from the local oscillator. These two signals are mixed to obtain an intermediate frequency or IF carrier through a process called heterodyning. This is done to recover the audio signal that was impressed on the RF carrier. The IF carrier is applied to an IF amplifier. The amplified IF carrier is then sent to a detector.
Figure 4.1-17 AM Superheterodyne Receiver
The output of the detector is the audio component of the input signal. This audio component is amplified and sent to a speaker or headphones for reproduction. A superheterodyne receiver may have more than one frequency converting stage and as many amplifiers as needed to obtain the desired power output.
The intermediate frequency is developed by heterodyning in the mixer stage, which is sometimes called a converter or first detector. The local oscillator tracks with the tuning of the incoming signal so that it produces a frequency higher or lower than the frequency of the incoming signal by the exact amount of the fixed IF frequency. Four frequencies appear at the mixer output. They are the incoming RF signal, the local oscillator signal, and the sum and difference of the incoming RF signal and local oscillator signal. The IF amplifier will be tuned to the difference, or intermediate, frequency. A typical IF for AM communication receivers is 455 kHz.
Once the IF stages have amplified the IF to a sufficient level, it is fed to the detector (or second detector, if referring to the mixer as first detector) to extract the audio signal. The detector stage consists of a rectifier and filter, which respond only to the amplitude variations of the IF signal in order to develop an output voltage varying at an audio frequency rate. The audio output from the detector is amplified in the audio amplifier to drive a speaker or headphones.
FM SUPERHETERODYNE RECEIVER
The function of a frequency modulated (FM) superheterodyne receiver is essentially the same as that of an AM superheterodyne receiver; however, there are circuit differences due to the change in modulating technique. A comparison of block diagrams (Figures 4.1-17 and 4.1-18) shows that in both AM and FM receivers the RF stage amplifies the incoming signal. The mixer combines the RF with a local oscillator RF frequency to produce the IF. Notice that the IF in the FM receiver is amplified by wideband IF amplifiers. The bandwidth for any type of modulation must be wide enough to pass all the frequency components of a modulated signal. The IF amplifier in an FM receiver has a broader bandpass than in an AM receiver because an FM signal inherently occupies a wider band than AM. Beyond the IF stage there is a marked difference between the two receivers. While the AM detector detects variations in amplitude in order to extract audio, an FM discriminator detects variations in frequency. The discriminator is preceded by a limiter that limits amplitude to minimize noise interference. We can do this because the amplitude variations do not contain intelligence. The detected audio signal is then amplified, as in the AM receiver. Electrically, there are only two fundamental sections of the FM receiver that are different from the AM receiver, the discriminator and limiter.
Advantages of FM
In normal reception, FM signals are free of static, while AM signals are subject to crackling noises and whistles. FM also has a greater number of frequencies available. FM signals provide a much more realistic reproduction of sound because of an increased number of sidebands.
Figure 4.1-18 FM Receiver Block Diagram
Disadvantages of FM
The disadvantage of FM is the wide bandpass required to transmit the FM signals. Each station must be assigned a wide band in the frequency spectrum.
Figure 4.1-19 illustrates the block diagram of a basic SSB receiver. It is not significantly different from a conventional superheterodyne AM receiver. However, a special type of detector and a carrier reinsertion oscillator must be used. The carrier reinsertion oscillator must furnish a carrier to the detector circuit at a frequency that corresponds almost exactly to the position of the carrier in producing the original signal. The filters used in the RF amplifier section of the SSB receivers serve several purposes. As previously stated, many SSB signals may exist in a small portion of the frequency spectrum. Therefore, filters used supply the selectivity necessary to adequately receive only one of the many signals that may be present. They may also select upper sideband or lower sideband operation when desired, as well as reject noise and other interference. SSB receivers may use additional circuits that enhance frequency stability, improve image rejection, or provide automatic gain control (AGC) however, the circuits contained in the basic receiver of Figure 4.1-19 will be found in all single sideband receivers. In SSB receivers extreme frequency stability is necessary because a small deviation from the correct value in local oscillator frequency will cause the IF produced by the mixer to be displaced from its correct value. In AM reception this is not too damaging, since the carrier and sidebands are all present and will all be displaced an equal amount. The relative positions of carrier and sidebands will be
Figure 4.1-19 Basic SSB Receiver Block Diagram
retained. However, in SSB reception there is no carrier, and only one sideband is present in the incoming signal. It is very important that the local oscillator and carrier reinsertion oscillator be extremely stable, otherwise the audio signal will be unintelligible.
BASIC COMMUNICATIONS RADIO SYSTEMS AND EQUIPMENT
A communications system is a collection of equipment configured to accomplish a specific communications requirement. For a pictorial view of a typical communications system containing the necessary components for transmission and reception of voice, CW, and teletype signals, refer to Figure 4.1-20. In the following section common LF, HF, VHF, and UHF communication equipment configurations are discussed.
The LF band is used for long range direction finding, medium, and long range communications,
and aeronautical radio navigation.
The LF transmitter is used to transmit a high-powered signal over very long distances. The AN/FRT-72 transmitter is designed for this purpose. The transmitter produces 50 kW peak envelope power (25 kW average power) and covers a frequency range of 30 to 150 kHz. LF
transmitters are normally used only on shore stations or for special applications.
The LF receiver is designed to receive LF broadcast signals and reproduce the intelligence that was transmitted. The LF signal received by antennas is sent to a multicoupler and patch panel.
Figure 4.1-20 Communications System
The multicoupler and patch panel (AN/SRA-17, AN/SRA-49) allow the operator to
select different antennas and connect them to different receivers, selecting the correct combination for a particular requirement. Examples of LF receivers are the AN/SRR-19A or R-2368A/URR. The AN/SRR-19A operates in the frequency range of 30 to 300 kHz, while the R-2368A/URR operates from 14 kHz to 30 MHz. The output of the receiver (audio) is fed to the SB-973/SRR receiver transfer switchboard. The switchboard can connect the receiver output to numerous pieces of equipment. Receiver output is connected to an AN/URA-17 or a CV-2460 converter comparator set. The set converts the received signal to DC for use by teletype (TTY) equipment. The DC output is fed to a DC patch panel, such as the SB-1203/UG. The DC patch panel permits the signal to be patched to any crypto equipment desired. The crypto equipment decrypts the signal and sends it to a red DC patch panel such as the SB-1210/UGQ. The SB-1210/UGQ can be patched to a selected teletype printer that prints the signal in plain text, or to a reperforator, where a paper tape is punched and stored, for printing at a later date. An LF receive system is shown in Figure 4.1-21.
Figure 4.1-21 LF Receive System
The HF band is used primarily by mobile and maritime units. The military uses this band for long range voice and teletype communications. This band is also used as a backup for the satellite communications system.
The HF transmit signal can contain either voice or teletype information. Figure 4.1-22 shows a typical HF transmit system used aboard ship.
Figure 4.1-22 HF Transmit System
The same equipment used to receive teletype messages on low frequencies (the teletype, DC Patch Panel SB-1210/UGQ, crypto equipment, and DC Patch Panel SB-1203/UG) is used to transmit teletype messages on the HF frequency system, in reverse order. An AN/UCC-1(V) or CV-2460 telegraph terminal converts DC signals into tone signals. The output of the AN/UCC-1(V) is connected to the SB-988/SRT transmitter transfer switchboard. A C-1004 control/teletype keys the transmitter during TTY operation. Voice signals from remote handsets connected to C-1138 radio set controls are also connected to this switchboard. The AN/URT-23 transmitter modulates an RF signal with the input signal. The modulated RF signal is connected to the AN/SRA-34, 56, 57, 58, or AN/URA-38 antenna coupler. The antenna radiates the signal into the atmosphere.
A typical HF receive system is shown in Figure 4.1-23. A transmitted signal, similar to the one just described in the previous section, is received by the antenna and converted to electrical energy. The signal is distributed to any number of receivers by an antenna patch panel. Receivers R-1051/URR, R-2368/URR, or R-1903/URR convert the RF signal into a teletype (FSK) or voice signal. The receiver output is routed through an SB-973/SRR receiver transfer switchboard to C-1138 or AM-3729 remote speaker amplifier.
Figure 4.1-23 HF Receive System
VERY HIGH FREQUENCY
The VHF band, 30 to 300 MHz, is used for aeronautical radio navigation and communications, radar, amateur radio, and mobile communications. The navy uses this band for mobile communications, such as for boat crews and landing parties, and bridge-to-bridge
communications. A basic block diagram of a VHF transmit and receive system is shown in
Figure 4.1-24. The AN/URC-80 and AN/VRC-46 are common VHF transceivers.
Figure 4.1-24 VHF Transmit and Receive System
The transmitter and receiver used in the UHF system form one piece of equipment and share common circuitry (a transceiver); however, the transmit and receive systems are discussed separately in the following paragraphs. Although this description pertains specifically to voice communication, UHF equipment also processes teletype data.
A basic block diagram of a UHF transmit system is shown in Figure 4.1-25. On the transmit side of the secure voice system, the operator at a remote location talks into the secure voice Remote Phone Unit (RPU). The RPU is connected to the secure voice matrix. The matrix is the tie point for the connection of more than one remote phone unit. The output of the matrix is connected to secure voice equipment, which encrypts the signal received. The output of the secure voice equipment in connected to an SB-988/SRT transmitter transfer switchboard.
The transmitter transfer switchboard is used to connect numerous remote phone units to any number of transmitters. The output of the patch panel is connected to the transmitter side of the AN/SRC-20, AN/SRC-21, or AN/WSC-3, which in turn is connected via an AN/SRA-33 or OA-9123 antenna coupler to the antenna.
A basic block diagram of a UHF receive system is shown in Figure 4.1-26. The received signal is picked up by the antenna and sent to the receiver side of the AN/SRC-20/21 or AN/WSC-3
through an AN/SRA-33 or OA-9123/SRC antenna coupler. The output of the receiver is
Figure 4.1-25 UHF Transmit System
connected to an SB-973/SRR receiver transfer switchboard, where it can be connected to either the nonsecure or secure voice system, depending on the mode of transmission. When a
nonsecure signal is received, the output of the receive transfer switchboard is connected to either
the C-1138 radio set control or the AM-3729 speaker amplifier, or both, depending on user preference.
Figure 4.1-26 UHF Receive System
If a secure voice transmission is received, the output of the receiver transfer switchboard is connected to secure voice equipment, where it is decrypted. The output of the secure voice equipment is connected to the secure voice matrix, which performs the same function as the matrix on the transmit system. The output of the secure voice matrix is connected to the secure remote phone unit, where the signal is converted back to its original form.
PORTABLE COMMUNICATIONS EQUIPMENT
Because portable and pack radio sets must be lightweight, compact, and self-contained, they usually are powered by a battery or hand generator, have low output power, and are either transceivers or transmitter-receivers. Navy ships carry these radio sets for emergency and amphibious communications. The numbers and types of portable equipment vary according to the individual ship.
The AN/CRT-3A radio transmitter, known as the "Gibson Girl," is a rugged emergency transmitter carried aboard ships and aircraft for use in lifeboats and liferafts. It is shown in Figure 4.1-27. No receive equipment is included.
Figure 4.1-27 AN/CRT-3A
The transmitter operates on the international distress frequency (500 kHz) and the survival craft communication frequency (8,364 kHz). It automatically repeats CW distress signals, shifting between 500 and 8,364 kHz every 50 seconds. The complete radio transmitter, including the power supply, is contained in an airtight and waterproof aluminum cabinet. The cabinet is shaped to fit between the operator's legs and has a strap for securing it in the operating position. The only operating controls are a three position selector switch and a pushbutton telegraph key. A handcrank screws into a socket in the top of the cabinet. The generator, automatic keying and automatic frequency changing are all operated by turning the handcrank. While the handcrank is being turned, the set automatically transmits the distress signal "SOS" in Morse code. The transmitter can be keyed manually, on 500 kHz only, by means of the pushbutton telegraph key.
Additional items (not shown) packaged with the transmitter include the antenna, a box kite and balloons for supporting the antenna, hydrogen-generating chemicals for inflating the balloons and a signal lamp that can be powered by the handcrank generator. The equipment floats and is painted brilliant orange-yellow to provide greatest visibility against dark backgrounds.
Radio Set AN/PRC-96
The AN/PRC-96 radio set (Figure 4.1-28) is a dual-channel, battery powered, portable transceiver that provides homing beacon signal and two-way AM voice communications between life rafts and by search and rescue ships and aircraft. It is a microminiature, solid state, hand-held radio that operates on the 121.5 MHz and 243 MHz guard channels. The AN/PRC-96 antenna is a 7.75-inch, rubber covered, omnidirectional, flexible whip antenna. The batteries supplied with the radio set are lithium D cells. Each cell is fused to protect against damage from external short circuits. Two cells are installed in the transceiver and four are packaged as spares.
Figure 4.1-28 AN/PRC-96
The AN/PRC-41 radio set (Figure 4.1-29) is a watertight, lightweight, portable UHF transceiver that may be operated on any of 1,750 channels spaced 100 kHz apart in the 225 to 400 MHz range. Its only mode of operation is AM voice, at an average output power of 3 watts. Although designed principally for manpack operation, the set may also be used for fixed station and vehicular operation when complemented by certain accessories. When not in use, the equipment is disassembled and stowed in a compartmentalized aluminum case similar to an ordinary suitcase.
Figure 4.1-29 AN/PRC-41
SINGLE AUDIO SYSTEM
The Single Audio System (SAS) was developed to fulfill the requirement for an integrated secure or nonsecure shipboard voice communications system. It consists of telephone sets, voice signal switching devices, various control devices, and field changes to existing equipments in conjunction with other existing elements of the radio communications system. The SAS is essentially a baseband (HF, VHF, or UHF) audio subset of the shipboard exterior communications system. It incorporates voice communications circuits, user control of the operating mode (secure and nonsecure) and various degrees of user control over circuit selection. There are two versions of SAS, automated (ASAS) and manual (MSAS). The principal differences between ASAS and MSAS are in their voice switching equipments and in the means provided for user control over circuit selection. (An example of user control is the choice of
desired communication channel.) Information in this section applies to both the ASAS and the MSAS unless otherwise specified. There is no specific list of equipment that constitutes an SAS installation. Equipment types and quantities are dictated by communications requirements.
The SAS provides the capabilities for configuring and operating voice communications circuits. A SAS installation permits secure or nonsecure communications at the discretion of the operator, from a single telephone or NTDS device. Interface with crypto or plain subsystems in the ship's communications system is the essence of the SAS. The SAS has the following capabilities:
lThe user can select the transmit operating mode except for FLTSATCOM secure voice and PLAIN configuration.
lThe system notifies the user of the transmit operating mode selected both visually and with audio indications.
lThe system notifies the user by visual indication if the voice station equipment is not connected to a crypto or plain subsystem.
lThe system notifies the user of any incoming CIPHER signals by both visual and audio indications except for the FLTSATCOM secure voice configuration.
lThe voice channel is selected by the user and indicated visually.
In addition to the capabilities listed above for the SAS, the ASAS version has the following features:
lA processor controlled, programmable voice switch
lA voice switch self test and fault location readout (BITE)
lThe system will notify the user (with audio indication) when the voice switch built-in-test (BIT) detects a line short
lA technical control monitor phone, incorporated into the voice switch, which can access all voice channels
User Station Equipment
User station equipment is located in various operations centers throughout the ship, such as the bridge, CIC, flag plot, secondary conn, and other stations where exterior voice communication is required by the ship's mission. This equipment consists of telephone sets, audio amplifiers, loudspeakers, headsets, recorders, audio jackboxes, NTDS consoles and intercom units, and local switching devices for system configuration flexibility.
Voice Switching Equipment
The voice switching equipment is a major component of the SAS. It is the interface and primary switch between the user's equipment and all crypto and plain subsystems. It is designed for very high interchannel isolation, a TEMPEST requirement for all equipments that handle both secure and nonsecure signals simultaneously. (The ASAS and MSAS use different switches for this function.)
Crypto and Plain Subsystems
Crypto and plain subsystems are located in the main communications spaces. Cryptographic devices and other "red" equipment are located in a secure area within these spaces. The crypto and plain subsystems used within the SAS are VINSON (UHF Secure Voice), Fleet Satellite Communications (FLTSATCOM) Secure Voice, and PLAIN ONLY. Additional classified information on these subsystems is available on a need-to-know basis.
Transmitter and Receiver Transfer Switchboards
This equipment is a part of the overall exterior communications switching system and is located in the main communications spaces, generally in the vicinity of the technical control working area. The switchboard equipment group interconnects crypto and plain subsystem equipment with the appropriate radio equipments. These switchboards are also the interconnecting points for other subsystems within the overall exterior communications system and are not unique to the SAS.
Transmit and Receive Radio Equipment
Radio equipment may be located in both the main communications spaces and in separate rooms located in various parts of the ship. This equipment group consists of the transmitters, transceivers, and receivers used for voice nets. The more common transceivers that you will encounter are the AN/SRC-20 series, AN/VRC-46, AN/WSC-3(V)3 and (V)7, AN/URC-93, and AN/WSC-6. Common transmitters include the AN/URT-23, AN/URT-24, T-1322/SRC, and AN/GRT-21. Common receivers are the R-1051 series, R-1903, and AN/GRR-23. For additional information on individual equipment, refer to the applicable technical manual.
The radio equipment group of the SAS interfaces with the usual RF components of the ship's exterior communications system. While these components must operate satisfactorily for the SAS to operate successfully, they have no direct application to the single audio concept and therefore are not discussed in this section. If you require additional information on RF components such as couplers, RF switches, and antennas, consult your ship's documentation.
SATELLITE COMMUNICATIONS FUNDAMENTALS
In the 1970s, when the HF spectrum was becoming overcrowded, free frequencies were at a premium, and HF jamming techniques were becoming highly sophisticated, the need for new and advanced long range transmission methods became apparent. Although HF communications will continue to provide limited opportunities for traffic delivery, the inherent uncertainties of HF propagation seriously impair the ability of commands to deliver high precedence command and control traffic. HF, while suitable for narrative traffic and intra-battle group communications, is not suited in terms of affordability for data rates above 1200 baud and, in comparison to SATCOM, is manpower intensive to operate. HF systems are susceptible to atmospheric absorption and HFDF and are the systems most susceptible to jamming. HF is considered more vulnerable to nuclear blackout than other frequencies, though ground waves are minimally affected. UHF SATCOM, SHF SATCOM, and modernized HF currently have the greatest potential for near-term contribution. Satellite systems provide reliable, high speed, high volume communications capabilities. The use of discrete UHF/SHF frequencies on satellite channels minimizes the effects of traditional jamming and interception. EHF systems are being developed and fielded. Note that affordability may constrain extensive HF modernization.
A satellite communication system uses satellites to relay radio transmissions between earth terminals. Communications systems use active satellites that amplify and retransmit RF signals. A signal is transmitted to the satellite on a frequency called the uplink frequency. The satellite transponder amplifies and translates this signal to the downlink frequency, and transmits it back to earth. This concept is illustrated in Figure 4.1-30, showing a variety of earth terminals.
Figure 4.1-30 Satellite Communication System
The design of a satellite communication system depends to a great degree on the satellite's orbit. An orbit is generally either elliptical or circular, with an inclined, polar, or equatorial orientation. A special type of orbit, called a synchronous orbit, has a period the same as the earth's rotation. Communication satellites are in equatorial synchronous orbits and therefore
appear stationary to an earth terminal. The area of the earth that a particular satellite covers is called the footprint, depicted in Figure 4.1-31.
Figure 4.1-31 Satellite Footprint
The following sections are divided into EHF, SHF, and UHF SATCOM and provide an introduction to SATCOM systems, subsystems, and equipment.
EHF SATELLITE COMMUNICATIONS
EHF SATCOM is the next generation of the military SATCOM systems, providing the services with interoperable and survivable SATCOM. The EHF portion of the frequency spectrum extends from 30 to 300 GHz. The extensive bandwidth available at EHF frequencies can be used for either high data rate transmission or for extremely robust anti-jam (AJ) communications. The currently funded EHF SATCOM programs take the latter approach, using the Satellite Data Link Standard (SDLS), limiting data rate to 2.4 kbps (bits per second). SDLS EHF SATCOM is primarily oriented toward intra-battle group tactical data information exchange. Note that a medium data rate (MDR) capability is being developed that provides some AJ performance at user data rates up to 1.544 Mbps. The disadvantages of EHF SATCOM are: the EHF portion of the spectrum is highly sensitive to atmospheric attenuation, the narrow beam makes interception difficult, and EHF is less vulnerable to the effects of nuclear blackout and scintillation. The EHF medium is suitable for record services, database exchange, voice, graphic data exchange, facsimile, imagery transmission, and video teleconferencing. EHF provides survivable wartime C3 for designated commanders and their assigned forces and AJ, low probability of intercept (LPI) minimum essential communications in a stressed environment for shore, ship and submarine platforms. The EHF satellite system consists of the space segment, control segment, and terminal segment.
EHF SPACE SEGMENT
The EHF space segment consists of the Fleet Satellite (FLTSAT) EHF Package (FEP), UHF Follow-On (UFO) with EHF Package (UFO/E), and Milstar satellites. FEP transponders ride on Fleet Satellites 7 and 8 and UFO/E rides on UFO satellites 4 and beyond. These satellites and Milstar satellites are being launched in 1990s. The FEP program was initiated to demonstrate and test certain key features of the Milstar EHF SATCOM system and to provide on-orbit test payload for operational test and evaluation of EHF terminals and initial operating requirements. FEP supports EHF uplink and SHF downlink communications using an earth coverage (EC) beam (a 17.5° view of the earth as seen by the satellite) and a spot beam (a steerable 5° spot beam covering a bounded geographical area.
The UFO/E SATCOM package provides an EHF uplink EC antenna, an SHF downlink EC antenna, and an EHF uplink/SHF downlink spot beam antenna. The uplink and downlink EC antennas will typically be used to support shore site terminals and the spot beam antenna will typically be used to support disadvantaged terminals, such as battle group terminals. These satellites will also replace aging UHF satellites. Milstar may feature satellites in both geostationary and highly inclined orbits in order to achieve virtually full earth coverage. The system features three type of arrays: an EC beam, three steerable spot beams providing a concentrated beam of energy within a bounded geographical area, and agile beams which are an array of fixed beams covering the view of the earth from the satellite to provide the best link beam coverage through electronic switching from beam to beam. The Milstar constellation is illustrated in Figure 4.1-32.
Figure 4.1-32 Milstar Configuration
All Milstar uplink antennas are at EHF except one, the UHF Air Force Satellite Communications antenna. Five downlink antennas are at SHF and two at UHF. Downlink capabilities are divided between spot beams, agile beams, and EC antennas.
EHF TERMINAL SEGMENT
The terminal segment consists of the terminals developed by the U.S. Navy, U.S. Army, and U.S. Air Force and the baseband systems that interface with all terminals. The three U.S. Navy EHF Satellite Communications Program (NESP) terminals are designed for use in surface ships, submarines, and at shore stations. The AN/USC-38(V)2 is the surface ship terminal. The AN/USC-38 is a general purpose communications terminal that uses an EHF uplink and SHF downlink. System design accommodates secure voice, teletype, data, and fleet broadcast systems. An AN/USC-38 ship terminal block diagram is shown in Figure 4.1-33. The AN/USC-38(V) is comprised of three major components: the CEG (Communication Equipment Group), HPA (High Power Amplifier), and Antenna Group.
Figure 4.1-33 AN/USC-38(V)1 Ship Terminal Block Diagram
SHF SATELLITE COMMUNICATIONS
SHF SATCOM terminals are installed in selected surface vessels to provide high capacity, AJ, real time command and control communications between naval force commanders and National Command Authorities (NCA). SHF SATCOM terminals are also installed in all Military Sealift Command Oceanographic Surveillance Ships (T-AGOS) to provide a path for acoustic data to the
two Naval Ocean Processing Facilities. Marine Expeditionary Forces also use SHF SATCOM terminals for long-haul connectivity during extended operations ashore. NCTAMS and selected NCTSs are the main termination points for U.S Navy SHF SATCOM. Increased connectivity with other DSCS and DCS users is planned involving the increased use of U.S. Army and U. S. Air Force facilities for access to DSCS. DSCS ground entry stations are shown in Figure 4.1-34.
The space segment of the U.S. Navy SHF SATCOM system consists of the DOD Defense Satellite Communications System (DSCS) satellite constellation and may use NATO/allied, and commercial (INTELSAT, AURORA, TESTAR 3) satellite constellations. The DOD SHF SATCOM system was implemented in phases and is an ongoing program which is operated, maintained, and controlled as a subsystem of the Defense Communications System (DCS). DSCS satellites (Phase I), which are no longer in use, provided the initial SHF SATCOM capability from 1967 to 1975. The first DSCS II satellite (Phase II) was launched in November 1971 and an additional 15 were launched in September 1989. Only four of the DSCS II satellites remain: two active and two in reserve. DSCS III satellites are designed to provide SHF SATCOM capability through the 1990s and are being placed in geosynchronous orbit above the equator, adjacent to DSCS II satellites. Both provide coverage between 75°N latitude and 75°S latitude. DSCS III satellites are designed for an operational lifespan of ten years. DSCS II satellites are being removed from service as DSCS III satellites are activated. DSCS III satellites provide substantial increases in performance capability to support high capacity links between all terminals and to permit AJ communications and control of satellites during crisis and contingency situations. The DSCS footprint is illustrated in Figure 4.1-35.
DSCS SHF carrier signals permit a large bandwidth that can be used for AJ signal processing at low and high user data rates. The navy uses both services and plans to extend the latter, seeking up to 1.544 Mbps non-AJ service per ship. The navy plans to install SHF SATCOM on most combatants, with initial focus on aircraft carriers, amphibious flagships, and flag-capable cruisers. Other considerations concerning SHF SATCOM are:
lSHF is less susceptible to jamming than UHF
lSHF AJ services are highly resistant to uplink jamming attack.
lNuclear air bursts degrade SHF by causing interruptions that vary in length depending on several factors.
SHF SATCOM is required on flagships to satisfy minimum tactical C2, intelligence, and warfighting communications requirements and improve Joint and Allied communications interoperability. SHF SATCOM is designated as the primary spectrum for Joint and
Allied/NATO interoperability. With a satellite constellation and world-wide shore terminals in
place, SHF SATCOM is capable of providing communication pipelines for all kinds of
information exchange. SHF terminals operating with DSCS will support wider bandwidth for greater throughput for digital data, voice, and imagery transmissions to meet tactical C4I and warfighting requirements including:
lUSAF Tactical Air Command's Computer Assisted Force Management System (CAFMS)
Figure 4.1-34 DSCS Ground Entry Stations
Figure 4.1-35 DSCS Satellite Coverage
lWorld-Wide Military Command and Control System (WWMCCS) Intercomputer Network (WIN)
lAdvanced Narrowband Digital Voice Terminal (ANDVT), TACTERM (Tactical Terminal) TACTERM ANDVT provides a full duplex connection ship-to-shore via satellite.
lSTel (Stanford Telecommunications)/STU-III (Secure Telephone Unit Level III) Direct Dial Secure Voice - contains imbedded crypto for secure voice communications, typically tied through the ship's telephone (PABX, i.e., Private Automated Branch Exchange), e.g., the Dimension 2000. Note that STU-111 can also use the commercial system INMARSAT (International Maritime Satellite), however this configuration does not automatically go secure. An "A/B" switch configuration would permit a choice of transmission media.
SHF terminals will support joint communications interface with shore GMF (Ground Mobile Force) multichannel networks via DSCS-GMF gateway stations to extend the range of terrestrial
communications and provide:
lSupport to U.S. Navy and Marine Corps C2 for combined arms amphibious operations
lDirect access to deployed tactical telephone and data/message switched networks
lImproved interoperability with Allied/NATO communications system via DCS - Naval Computer Telecommunication System (NCTS) interface.
SHIPBOARD SHF TERMINALS
Shipboard AN/WSC-6(V) Terminal
The AN/WSC-6(V) is designed for use on surface ships to satisfy SHF ship-to-shore communication requirements while remaining within the cost, weight, and size constraints of the shipboard environment. The AN/WSC-6(V) consists of a radio group and antenna group. The radio group can interface with either of two antenna group configurations, a single or dual antenna. Surveillance Towed Array Sensor System (SURTASS) T-AGOS class ships use a AN/WSC-6(V)1 with a MD-1030A binary PSK modem and single antenna system. Flag and selected fleet units use the AN/WSC-6(V)2 with an OM-55(V)/USC spread spectrum AJ modem and TD-1389(V) low rate multiplexer and single or dual antenna. The antenna is pedestal mounted 4-foot parabolic reflector enclosed in a radome.
Shipboard QUICKSAT Terminal
QUICKSAT was been fielded to provide flagships with immediate capability to access the DSCS for improved C4I support and enhanced interoperability. A typical QUICKSAT system configuration is depicted in Figure 4.1-36. Tactical SHF SATCOM terminals are modified USAF AN/TSC-93B GMF SHF terminals on loan from the USAF. The AN/TSC-93B is being modified and installed on ships as QUICKSAT terminals. These terminals are modified to use the SURTASS (Surveillance Towed Array Sensor System) modem (MD-1030A), AN/WSC-6 tracking antenna (AS-3399), and AN/FCC-100(V) multiplexer. The QUICKSAT terminal is a transition system fielded under an accelerated implementation of the navy's phased program to expand SHF SATCOM support to the fleet. The AS-3399/WSC Antenna System (single or dual) used with the AN/WSC-6 SHF SATCOM terminal is mated to the modified AN/TSC-93B. This antenna is shown in Figure 4.1-37. Shipboard users of QUICKSAT are commanding officers and embarked commanders and their staffs. In a BG operating environment, enhanced communications capabilities can be extended to ships and staffs in company. Examples of user circuits include:
lSTel/STU-III for access to Public Switched Telephone Network (PSTN) or Defense Switched Network (DSN)
lNAVMACS (Navy Modular Automated Communications System) access to NAVCOMPARS (Naval Communications Processing and Routing System) via MARCEMP (Manual Relay Center Modernization Program)
lControl Orderwire (Orderwire circuits are used by operators to operate, maintain, and align communications links.)
lDual ANDVT/KYV-5 access to NCTAMS SRWI (Satellite Radio Wireline Interface)
Figure 4.1-36 Typical QUICKSAT System Configuration
lAccess to WIN
lTactical Environment Support System (TESS) for environmental support data (weather, atmospheric, oceanographic)
lStreamlined Alternative Logistic Transmission System (SALTS) for logistics and administrative data exchange (a desktop computer system using standard telephone lines and a STU-III for encryption). SALTS has automated INMARSAT dial up and connection, floppy disk data transfer from other shipboard systems (including SNAP), 8-1 data compression, simultaneous multiple file transfer, and data preparation and distribution without human intervention.
Figure 4.1-37 AS-3399/WSC Antenna
lLANTDIS (Atlantic Command Deployable Intelligence System) for access to DOD Intelligence Information System (DODIIS)
lCAFMS (Computer Assisted Force Management System)/CTAPS (Contingency TACS Automated Planning System) for access to USAF CTAPs
The composition of shipboard terminals is shown in Table 1.4-2. Note that these terminals are only interoperable through an intermediate shore site.
║TERMINAL │ANTENNA │SHF MODEM │BASEBAND │AJ/ ║
║TYPE │CONFIGURATION │ │MULTIPLEXER │NON-AJ ║
║AN/WSC-6(V)1 │Single │MD-1030A(V) │N/A │Non-AJ ║
║(SURTASS) │ │ │ │ ║
║AN/WSC-6(V)2 │Single or Dual │OM-55(V)/USC │TDM-1389(V) LRM │AJ ║
║(SATURN) │ │ │ │ ║
║AN/TSC-93B │Single or Dual │MD-1030A(V) │AN/FCC-100(V)1/2 │Non-AJ ║
║(QUICKSAT) │ │ │LSTDM │ ║
Table 1.4-2 Shipboard SHF Terminals
SHF SPACE SEGMENT
SHF terminals use DSCS satellite constellation access for ship-shore-ship communications. The navy uses the Navy Subnet of DSCS on the DSCS SHF transponders, which also supports SURTASS SHF SATCOM terminals, as the channel for SHF terminal operations. DSCS Navy Subnet and NCTS resources for QUICKSAT terminal support are managed by NCTAMS LANT for Atlantic and Mediterranean communication areas and NCTAMS EASTPAC for Eastern and Western Pacific, Persian Gulf, and Indian Ocean communications areas.
SHORE DSCS EARTH TERMINAL/GROUND ENTRY STATION
The earth segment of DSCS SHF SATCOM consists of those satellite terminals assigned to the U.S. Navy, U.S. Army, U.S. Marines, and U.S. Air Force for operation and maintenance. SHF SATCOM terminals in DSCS include fixed shore, Ground Mobile Force (GMF), jam-resistant secure communications, airborne, shipboard, and Diplomatic Telecommunication System terminals. Navy SATCOMMFACs and other DSCS facilities serve as ground entry stations to provide real-time link data management. These stations provide an interface into the DCS, NCTS, commercial communications systems, and selected Allied/NATO systems. The earth segment serves the following basic functions:
lReceives transmit IF signals from one or more modulators, up-converts the IF signals to satellite carrier frequencies, amplifies the carriers to the appropriate level, and transmits these carriers through a directional antenna to the satellite.
lReceives satellite downlink signals at the directional antenna, amplifies the signals in a low noise amplifier, down-converts the amplified signals to IF, and passes the IF to one or more demodulators.
SHF earth terminals used with the DSCS are the AN/GSC-39(V) medium size ground terminal designed for transportable requirements, AN/GSC-52(V) fixed or mobile medium size ground terminal, and AN/FSC-78(V) fixed heavy terminal. These terminals are located worldwide in support of the Eastern Atlantic, Western Atlantic, Indian Ocean, Eastern Pacific, and Western Pacific satellite coverage areas.
GMF SHF SATCOM terminals operate as a special user subnet through the DSCS to extend the range of terrestrial communications with improved reliability, speed, and deployment setup time to ground users. It supports the need to exchange communications traffic during all phases of training exercises and actual conflicts. GMF terminals can be deployed in subnetworks ranging in complexity from a small independent cluster to an elaborate network capable of supporting a joint mission. GMF terminal equipment includes the AN/TSC-85B, AN/TSC-93B, AN/TSC-100B, and AN/TSC-94B. The AN/TSC-85B and AN/TSC-93B provide connectivity between Marine division, air wing, support headquarters (HQ) and marine amphibious forces via theater HQ to Army Corps and division HQ and brigade command posts. The AN/TSC-100B and AN/TSC-94B provide connectivity between theater HQ and tactical air control centers, air bases, reporting posts, and support radar.
An SHF termination normally includes an orderwire with the terminating station for use in alignment, maintenance, and operation of the SHF communications link. Additional teletype circuits may be added as dictated by communications planners. When using the OM-55(V)/USC, link and net orderwires are 75 bps.
SHF Broadcast Network
This network will be a U.S. Navy-unique high speed shore-to-ship system with limited AJ capability. Existing requirements include SI, weather, message traffic, one-way secure voice, and imagery.
World Wide Military Command and Control System (WWMCCS) Afloat
WWMCCS is a network of systems that range from the national to theater level in support of national level C2 functions. WWMCCS interfaces with other non-WWMCCS systems, non-DOD agency systems, and tactical C2 systems that support subordinate military units. Present U.S. Navy shipboard users employ IBM compatible workstations to access WWMCCS. Future users will employ workstations based on Apple/McIntosh computers developed under the WWMCCS ADP Modernization Program (WAM). WWMCCS software standardization will enable U.S. Navy users to access the overall system. With the WWMCCS Intercomputer Network (WIN), users can communicate with other users, review and update information with inputs from other WWMCCS locations and transfer data accurately and rapidly between computers. Terrestrial and satellite connections permit real time TS communications.
Computer Assisted Force Management System (CAFMS)
CAFMS is a U.S. Air Force ADP system designed to provide air mission planning and monitoring support to augment Tactical Air Control System functions with information processing, storage, and display capabilities. CAFMS allows planners to generate strike mission packages or modify then for higher priority targets in theater. CAFMS uses the ORACLE database to provide automated assistance. The Contingency Tactical Air Control System (CTAPS) is being designed as a CAFMS upgrade. CAFMS software will be used within CTAPS.
Advanced Narrowband Digital Voice Terminal (ANDVT) is a standard military secure voice and data terminal designed for airborne, land-based, and shipboard communications. ANDVT is used for ship-shore-ship secure voice. ANDVT includes the TSEC/KYV-5 cryptoset, vocoder, and AN/USC-43 rack mount. ANDVT can operate in simplex (as for HF communications) or duplex. The ANDVT replaces CV-3333 and TSEC/KG-30 series narrowband secure voice equipment.
Secure voice connectivity between the afloat ANDVT user and shore third generation STU-III users is made via shore Satellite Radio Wireline Interface (SRWI). The STU-III telephone is used with SHF SATCOM for secure voice and data at all security levels. STU-III is capable of operating secure and non-secure however, SHF communications are always secure (vice STU-III communications via INMARSAT).
Use of Stanford Telecommunications (STel) modems (STel 9610 and 9620) allows ship-shore-ship direct dial capability. In a typical arrangement, the Stel 9610 provides the interface between the ship's telephone system and the ship's satellite terminal. The STU-III interfaces directly with the ship's Private Automated Branch Exchange (PABX), i.e., phone system (e.g., the Dimension 2000). The STU-III is also capable of communicating secure data from standard data terminal equipment (a PC), or facsimile machine using the STU-III's internal crypto device and modem. This feature allows the transfer of secure data over standard dial-up telephone lines to a remote location similarly equipped with a STU-III and peripheral equipment.
Demand Assigned Multiple Access (DAMA)
The expanded use of U.S. Navy SATCOM will include an SHF DAMA network for dynamic reconfiguration of multiple access requirements and a planned 64 kbps data rate. DAMA will be discussed in greater detail under UHF SATCOM.
UHF SATELLITE COMMUNICATIONS
UHF SATCOM is relatively easy to use, earth terminals are relatively inexpensive, and the space segment is less expensive than SHF or EHF to build, launch, and maintain orbit. The disadvantages of UHF SATCOM are that it can be blacked out for hours at a time by nuclear bursts and therefore is virtually unusable in an intensive nuclear environment, and it experiences interference from scintillation coincident to high solar storm activity.
UHF SATELLITE COMMUNICATIONS OVERVIEW
Fleet Satellite Communications (FLTSATCOM)
The FLTSATCOM system is a DOD resource managed and operated by the U.S. Navy. U.S. Air Force capabilities are employed to execute station keeping tasks for the space segment. From the early 1900s the U.S. Navy relied on HF radio as the principle transmission media for long distance communications. This situation began to change in 1965 when the three Services initiated studies on the use of SATCOM. Lincoln Laboratory Experimental Satellite 5 (LES 5), a UHF repeater satellite, was placed into high orbit on July 1, 1967. In September 1968 LES 6 was launched in further support of the tactical communications study program. An experimental tactical communications satellite (TACSAT-1) was launched in February 1969. TACSAT-1 was
used by all the military services in the assessment of the tactical role of SATCOM. Three
Maritime Satellite (MARISAT) system satellites developed by the Communications Satellite Corporation (COMSAT) were placed in orbit over the Atlantic (LANT), Pacific (PAC), and Indian Oceans during 1976. The U.S. Navy leased the UHF transponder of each satellite and
referred to these assets as GAPFILLER. This title distinguished the U.S. Navy leased capability from the rest of MARISAT and identified their function as a gapfilling measure pending the launch of Fleet Satellites (FLTSAT). Six FLTSATs launched between 1978 and 1989 provided the initial FLTSATCOM system. In addition, four satellites were leased between 1984 and 1990 from Hughes Aircraft (now Hughes Communication Services, Inc.) under the LEASAT program.
The FLTSATCOM system has been redefined to include the FLTSAT, LEASAT, and GAPFILLER satellites. The original leases of LEASAT-1, 2, and 3 have expired and these satellites were purchased by the DOD. These assets are managed by the U.S. Navy. The LEASAT-5 lease will expire in 1997 and will be DOD-owned in the future. The UHF Follow-On (UFO) program will provide satellites to replenish the aging FLTSATCOM system. FLTSATCOM satellites in four equatorial geosynchronous orbits over the LANT, CONUS, PAC, and IO (Indian Ocean) areas provide worldwide satellite coverage.
UHF Follow-On (UFO)
UFO satellites are designed to provide continuous, reliable, global UHF SATCOM to mobile and shorebased users. All UFO satellites have UHF and SHF capabilities. Additionally, satellite four and beyond will have an EHF capability. The UHF payload will consist of twenty-one 5 kHz channels, seventeen 25 kHz channels, and a broadcast channel with SHF uplink. Deployment of nine UFO satellites (eight operational satellites, two each over four ocean areas and one on-orbit spare) is scheduled through 1996. There was an unsuccessful launch in March 1993 and a successful launch in September 1993, placing the first UFO satellite in orbit over the IO.
International Maritime Satellite (INMARSAT)
Although the commercial INMARSAT system falls outside of the U.S. Navy portion of the UHF spectrum, it can be used to provide support to surface units at sea. The INMARSAT system is a multi-country controlled SATCOM network that links an INMARSAT terminal into existing national or international telephone networks. INMARSAT service is available to commands with an authorized installed INMARSAT terminal. U.S. Navy ships equipped with INMARSAT terminals are authorized to establish direct communications with shore commands or other USN/USNS INMARSAT equipped ships via INMARSAT earth stations operated by COMSAT General. Interface via NCTC facilities is not required. Use of NSA-approved crypto systems is mandatory. INMARSAT satellites provide worldwide coverage between 76°N and 76°S.
NATO UHF SATCOM Subsystem
The NATO UHF SATCOM subsystem was launched in 1991, has a design life of seven years, and is operated by NATO. The NATO UHF SATCOM subsystem consists of two UHF channels
on the NATO IV SHF satellite. It provides connectivity between subscribers and the NATO Integrated Communications System. U.S. Navy vessels operating in NATO areas may be required to enter the NATO UHF SATCOM subsystem.
Air Force Satellite Communications (AFSATCOM)
The AFSATCOM program provides reliable, worldwide C3 to designated Single Integrated Operational Plan/nuclear capable forces for emergency action message dissemination, Chairman JCS/CINC internetting, force direction, and force report-back communications. Additionally, AFSATCOM provides support for contingency/crisis operations, exercises, and training. The AFSATCOM space segment consists of U.S. Air Force managed transponders installed on FLTSATs and LEASATs and a terminal segment consisting of a family of UHF or SHF ground and airborne terminals. The AFSATCOM satellite platforms are in highly inclined elliptical orbits over the north polar regions.
FLEET SATELLITE COMMUNICATIONS
The U.S. Navy Fleet SATCOM system allows two-way ship-to-shore, shore-to-ship, and ship-to-ship communications using satellites in geostationary orbit over the Atlantic, Indian, and Pacific Oceans. The following satellites provide worldwide communications between 70° north and 70° south: FLTSAT, LEASAT, and MARISAT. The portion of MARISAT leased by the navy, GAPFILLER, augments FLTSAT and LEASAT until a sufficient number of next generation satellites, UFO assets, are available. Control of the MARISAT system was transferred to INMARSAT (International Maritime Satellite) in 1982. These satellite are essentially UHF, but also have SHF uplink capability. They have 23 separate RF channels: ten 25 kHz narrowband channels, twelve 5 kHz narrowband channels, and one 500 kHz wideband channel. The use of DAMA (Demand Assigned Multiple Access) multiplexers allows several baseband subsystems to share a single satellite channel, increasing the capacity of each satellite channel to up to four circuits. FLTSATs can be used with DAMA and non-DAMA configurations. Figure 4.1-38 depicts UHF fleet satellite coverage. The earth segment of UHF SATCOM consists of earth terminals that are located at NCTAMSs, NAVCOMMSTAs, and NAVCOMTELSTAs. The earth segment includes antennas, transmitters, receivers, baseband equipment, and subsystems ashore and afloat.
UHF SATCOM Shipboard Antennas
Antenna Groups OE-82B/WSC-1(V) and OE-82C/WSC-1(V) (shown in Figure 4.1-39 and
4.1-40, respectively) are designed for shipboard installations and interface with AN/WSC-3(V) transceivers. Each configuration consists of an antenna, bandpass amplifier-filter, switching unit, and antenna control. One or two antennas may be installed providing a view of the satellite at all times.
Navy UHF SATCOM Subsystems
Although any part of the Navy UHF SATCOM System can be operated as a separate entity, the integrated system provides connection for message traffic and voice communication networks to DOD long haul communication networks. The system consists of information exchange subsystems that use satellites as relays to exchange communications data among shore sites, ships, submarines, aircraft, and mobile units, and quality monitoring subsystems that provide data to manage satellite resources. Various shipboard systems and subsystems collect communications
Figure 4.1-38 UHF Satellite Coverage
Figure 4.1-39 OE-82B/WSC-1(V)
Figure 4.1-40 OE-82C/WSC-1(V)
data for processing. The following subsystems address specific naval communications requirements. FSB, CUDIXS, NAVMACS, SSIXS, SECVOC, TACINTEL, TTY, OTCIXS, TADIXS, DAMA, Control, TRE, TRAP and FIST will be discussed in greater detail.
lFleet Satellite Broadcast (FSB) Subsystem - an expansion of Fleet Broadcast transmissions that historically have been the central communications medium for operating naval units.
lCommon User Digital Information Exchange Subsystem (CUDIXS)/Naval Modular Automated Communication Subsystem (NAVMACS) - a network that is used for transmission of general service message traffic between designated ships and shore installations.
lSubmarine Satellite Information Exchange Subsystem (SSIXS) - complements existing communications links between SSBN and SSN submarines and shore terminals.
lSecure Voice Subsystem (SECVOX) - a narrowband UHF subsystem that links voice communications between ships and connects wide-area voice networks ashore.
lTactical Intelligence Information Exchange Subsystem (TACINTEL) - specifically designed for special intelligence communications.
lTeletypewriter Subsystem - an expansion of terrestrial teletypewriter transmission networks.
lOfficer in Tactical Command Information Exchange Subsystem (OTCIXS)/Tactical Data Information Exchange Subsystem (TADIXS) - provides a communications link that exchanges OTH-T (Over-the-Horizon Targeting) information from shore stations to fleet users in support of navy cruise missile operations.
lDemand Assigned Multiple Access (DAMA) Subsystem - developed to multiplex several subsystems, or users, on one satellite channel. This has the effect of allowing more satellite circuits to use a UHF satellite channel.
lControl Subsystem - a communications network that facilitates status reporting and management of FLTSATCOM system assets.
lLEASAT Telemetry, Tracking, and Command Subsystem - a joint operation by navy and contractor for LEASAT satellite control.
lSatellite Monitoring Subsystem - provides users of the UHF Satellite Communications System with means to analyze and resolve system and equipment related problems. The current subsystem is the interim FLTSATCOM Spectrum Monitor (IFSM) which will be replaced by the SATCOM Signal Analyzer (SSA).
lTactical Data Information Exchange System Broadcast B (TADIX B)/ Tactical Receive Equipment (TRE) - receives, demodulates, decodes, decrypts, processes, and distributes TADIX B broadcasts contact reports.
lTRE and Related Applications (TRAP) Subsystem - provides near real-time contact report data to a variety of AN/USQ-101(V) Tactical Receive Equipment users.
lFleet Imagery Support Terminal (FIST) Subsystem - transmits imagery shore-to-ship, ship-to-shore, ship-to-ship, or shore-to-shore.
Ship Based Terminals
The installation of subsystem equipment aboard ships (and aircraft) is determined by communications traffic levels, types of communications, and operational missions. Fleet Satellite Broadcast message traffic, as a common denominator for naval communications, will be received by all of units. In some installations, such as large ships, the Fleet Broadcast receiver is one part of the FLTSATCOM equipment suite. A typical suite on a large ship may include Fleet
Broadcast, CUDIXS/NAVMACS, Secure Voice, TADIXS/OTCIXS, Teletype, and TACINTEL equipment.
Shore Based Terminals
FLTSATCOM shore terminals are installed at four NCTAMSs which bear prime responsibility, in selected geographical areas, for naval communications via FLTSATCOM satellites. These stations are as follow:
lNCTAMS LANT, Norfolk, VA
lNCTAMS MED, Bagnoli, IT
lNCTAMS WESTPAC, Finegayan, Guam
lNCTAMS EASTPAC, Wahiawa, HA
lNCTS Stockton, CA
lTen NCTSs used to retransmit Fleet Broadcast message traffic via HF links. Additionally, at Yokosuka, Japan, there is an RF terminal for transmission of SSIXS and Secure Voice communications for the Western Pacific and Indian Oceans, and there is a landline between Japan and NCTAMS WESTPAC to support TADIXS and OTCIXS transmissions. There are additional shore-based sites.
Each subsystem consists of baseband equipment and the RF terminal. Baseband equipment is used to collect and control transmitted or received information. RF terminals are used by the baseband system to transmit and receive via satellite. UHF SATCOM terminal equipment includes AN/WSC-5(V) transceivers and the AN/FSC-79 SHF terminal. Most subsystems use a common RF terminal. One exception is Fleet Broadcast, which has its own terminal. The RF terminal and baseband equipment may not be collocated.
CUDIXS baseband equipment is connected to the NAVCOMPARS. NAVCOMPARS channels general-service message traffic for transmission on the CUDIXS RF link and collects message traffic for Fleet Broadcasts transmission. NAVCOMPARS may be interfaced with AUTODIN switching centers to provide automatic connectivity with DOD communications networks.
TADIXS Gateway Facilities (TGF) provide access to TADIXS and OTCIXS communications links. Surveillance and targeting data inputs to TADIXS TGF are provided via a Tactical Data Processor Controller (TDPCON). Data inputs vary from installation to installation. Each TDP (Tactical Data Processor) that is authorized access to TADIXS and/or OTCIXS is provided a TDPCON. The TDPCON relays data via landline/microwave to the TGF for routing and satellite access.
Secure voice (SECVOX) is connected to UHF and SHF terminals and to the AUTOSEVOCOM (Automatic Secure Voice Communications) network. The interface to AUTOSEVOCOM extends voice coverage of the SECVOX subsystems beyond the immediate area of the NCTAMS.
FLEET SATELLITE BROADCAST SUBSYSTEM
The SHF (AJ) Fleet Satellite Broadcast Subsystem provides the capability to transmit Fleet Broadcast message traffic in a high level jamming environment. The subsystem has 15 subchannels of encrypted message traffic at an input data rate of 75 bps. These subchannels are time division multiplexed and transmitted in a one way SHF transmission to the satellite at 1200 bps. At the satellite, the transmission is translated from SHF to UHF for transmission on the downlink to the subscriber.
Fleet Broadcast message traffic is queued and/or channelized prior to transmission by two processor-controlled message switching systems. These systems are the NAVCOMPARS, for general service (GENSER) message traffic and STREAMLINER, for special intelligence message traffic. Fleet weather data, from Naval Oceanographic Command Centers, is also transmitted on non-processor controlled Fleet Broadcast channels. The structure of the fleet broadcast transmission provides 15 subchannels for GENSER message traffic, SI message traffic, and fleet weather data, each operating at 75 bps. A sixteenth subchannel is used for frame synchronization.
GENSER message traffic is entered into the NAVCOMPARS processor at NCTAMS/NCTS or input automatically into the processor when the message traffic is received from the AUTODIN switching center. The same general process is applicable for entering SI messages from the STREAMLINER processor. Fleet weather data are input directly to the system by teletypewriter or record-reproducer. The queued/channelized message traffic from these three collection points is encrypted, multiplexed, and transmitted by the AN/FSC-79 or AN/WSC-5(V) on SHF or UHF uplink.
Subscribers receive the UHF downlink signal with the AN/SSR-1, 1A receiver system. The demultiplexed output data stream from the receiver is decrypted and read into NAVMACS or TACINTEL processors for message screening and printing. Weather data are sent to teleprinters. Non-automated ships, i.e., subscribers that do not have NAVMACS or TACINTEL processors, guard selected fleet satellite broadcast subchannels and output the data directly to teleprinters or processors. A diagram of the Fleet Satellite Broadcast Subsystem is provided in Figure 4.1-41.
Figure 4.1-41 Fleet Satellite Broadcast Subsystem
CUDIXS and NAVMACS are shorebased automated GENSER communications processing systems that interface the automated processing features of NAVCOMPARS ashore with subscribers afloat. CUDIXS and NAVMACS consist of processors and peripherals that handle high volume two-way fleet message traffic and provide RF link control for efficient operation of the ashore and afloat network. These subsystems have improved message traffic throughput and volume and improved link reliability by exploiting the speed and reliability of UHF SATCOM.
CUDIXS consists of shore based processors and peripherals and serves a network of up to 60 subscribers. CUDIXS and NAVMACS subsystems use the network and a 25 kHz satellite channel to exchange message traffic. CUDIXS baseband equipment shares a common AN/WSC-5(V) with other subsystems (e.g., SECVOX, SSIXS). The CUDIXS terminal acts as both a link controller for the network and a member of the network. To maintain link control the CUDIXS processor transmits a sequence order list to network subscribers, specifying transmit order and length of transmission. Based on the sequence order list, subscribers calculate when to transmit message traffic. Subscriber request access to the net and are allowed to screen incoming message traffic. NAVMACS processor installations are required to screen CUDIXS message traffic and up to four channels of fleet broadcast.
NAVMACS subsystem capability is dependent on the version of NAVMACS installed. The satellite signal is received by an OE-82 antenna and AN/WSC-3 transceiver, screened by the ON-143 interconnecting group, decrypted by a TSEC/KG-35 or 36, processed by the AN/UYK-20. The AN/UYK-20 routes message traffic to peripheral equipment. Ships with a Communication Data Processing System (CDPS) installed do not screen messages with NAVMACS. A diagram of the CUDIXS/NAVMACS Subsystem is provided in Figure 4.1-42.
SSIXS augments terrestrial VLF and LF/MF/HF communications links between shore-based submarine Broadcast Control Authorities (BCA) and submarines. This subsystem provides submarine commanders with the means to receive group broadcast messages via satellite at scheduled times. Submarine commanders can actively request messages held in queue by the BCA or passively receive group broadcasts. A 25 kHz channel on FLTSAT and/or LEASAT has been allotted to SSIXS. SSIXS shore sites have undergone a major upgrade, SSIXS II, that replaces shore equipment with new computer equipment. SSIXS II baseband equipment at BCAs perform two functions:
lAccept messages (from AUTODIN, NAVCOMPARS, or over-the-counter in message centers) for transmission to submarines via satellite/VLF paths. Receive and forward messages from submarines via satellite.
lProvide shore SSIXS operators with capability to compose and control VLF VERDIN broadcast by an interface with the Integrated Submarine Automated Broadcasts Processing System (ISABPS).
Figure 4.1-42 CUDIXS/NAVMACS Subsystem (Non-DAMA)
Messages addressed to submarines are entered into the SSIXS shore terminal using operator console keyboards, high speed paper tape readers, and the Submarine Message Automated Routing Terminal (SMART). Messages sent by submarines are entered input via teletypewriter or tape reader equipment. SSN submarines with that have the Data Link Control System (DLCS) have an additional input/output capability via the Sensor Interface Unit (SUI) for
OTH-T messages. BCAs ashore are connected to NCTAMS by modems and landlines. Ashore, SSIXS uses the same RF terminal equipment used for other UHF SATCOM subsystems, with the exception of COMSUBGRU SEVEN in Yokosuka, which has dedicated AN/WSC-3s. In addition to GENSER SSIXS, a SSIXS capability dedicated to special intelligence communications, designated SI SSIXS is available at all BCAs. A diagram of the SSIXS Subsystem is provided in Figure 4.1-43.
The Secure Voice (SECVOX) subsystem provides the means for transmission of ship-to-ship, ship-to-shore, and shore-to-ship SECVOX communications. These subsystems have dedicated channels or DAMA time slots on FLTSAT and/or LEASAT. Ship-to-shore voice communications beyond the immediate area of NCTAMS/NCTS is provided by AUTOSEVOCOM extension. NCTAMS/NCTS maintains channel control. Mobile users (aboard ships and submarines) may access a SECVOX RF channel not in use to communicate directly to other mobile platforms. When coordinating voice communications with a shore command, the mobile user contacts the voice controller. The voice controller alerts the recipient of the incoming transmission. If channels are busy, or if communications procedures direct, the user must send a message request for a voice channel to the controller using the CUDIXS/NAVMACS RF network. Submarines use the SSIXS net. The controller then coordinates and authorizes transmission on a SECVOX channel. A diagram of a SECVOX Subsystem is provided in Figure 4.1-44.
Ship-to-Shore-to-Ship SECVOX communications are provided through the use of Satellite Radio Wireline Interface (SRWI) equipment located at naval communications facilities ashore. SRWI is designed to integrate existing and future SECVOX communications subsystems including terrestrial (wireline) links; UHF, SHF, and EHF SATCOM links; and HF links. SRWI provides the capability to connect the shore-based worldwide wireline systems with SATCOM, DSCS (Defense Satellite Communications System), and alternate HF systems to extend shore communications seaward. Specifically, SRWI provides interface to:
lSecure Voice Improvement Program (SVIP) channels (STU-III units) for non-tactical voice communications
lLocal RED telephone bus (TA-970 or equivalent)
lANDVT (Advanced Narrowband Digital Voice Terminal) AN/USC-43(V)1 SATCOM radio terminals (UHF, SHF, planned EHF)
lHF secure radio links
Figure 4.1-43 SSIXS Subsystem
Figure 4.1-44 SECVOX Subsystem (Final DAMA Configuration)
SRWI affords operators the necessary functions to emulate operator control. The shore operator can act as net controller, if required. The shore operator can interface any two compatible subscribing channels.
Ship-to-Ship SECVOX communications are provided using ANDVT or CV-3333 and KG-36 equipment on either dedicated SATCOM channels or standard SATCOM DAMA time slots.
TACINTEL is used for special-intelligence communications (up to SCI). The subsystem is a computerized message processing installation that enables transmit and receive message traffic via satellite in a controlled environment and processes time-sensitive sensor and essential data on a priority basis and not in narrative format. Unlike CUDIXS/NAVMACS, TACINTEL is capable of direct ship-to-ship interchange of this data, but not narrative record messages. Message traffic can be read into TACINTEL peripheral equipment such as tape readers (not ashore) or the display terminal keyboard. Most traffic is entered automatically by systems/facilities connected to TACINTEL. TACINTEL baseband equipment uses an RF terminal in common with other subsystems at shore facilities and subscriber installations.
The Combat Direction Finding TACINTEL Terminal (CDFTT) combines existing functions of TACINTEL equipment in a rack-mounted configuration and uses software to automate human/machine requirements. The development model of the CDFTT is the ON-234(XG-1). The future TACINTEL II Subsystem will be a computer-based message communication system that automatically receives, routes, and transmits SI on a priority basis for ashore and afloat users. It will remain interoperable with the present TACINTEL during transition. Communication across a mix of media will be possible, including UHF LOS, UHF Satellite, SHF Satellite, EHF Satellite, HF, and Fiber Optic Landline (FOL). A diagram of the TACINTEL Subsystem is provided in Figure 4.1-45.
The Teletypewriter (TTY) Subsystem is an expansion of existing 75 bps TTY communication networks, using satellites as relay stations. Applications for TTY circuits include dedicated terminations for beyond LOS (BLOS) tactical and report-back circuits as well as circuits for contingency use and as back-up connectivity for networks such as CUDIXS/NAVMACS and TACINTEL. A diagram of the TTY Subsystem is provided in Figure 4.1-46.
Figure 4.1-45 TACINTEL Subsystem (DAMA Configured)
Figure 4.1-46 TTY Subsystem (DAMA Configured)
This subsystem supports the exchange of OTH-T (Over-the-Horizon Targeting) information ship-to-ship and between shore and fleet-based computer systems (collectively referred to as TDPs or Tactical Data Processors) in support of U.S. Navy cruise missile operations. OTCIXS provides a tactical two-way SATCOM network primarily used for ship-to-ship (organic to the BG) exchange of targeting information (up to SI) by teletype and data link message. TADIXS was designed to exchange non-organic tactical data link information with worldwide connectivity. Note that OTCIXS does have inter-theater connectivity through NCTAMS gateway terminals and satellites however, this is not the fastest means of data exchange and not normally used. Data is input to the TGF via a TDP Controller (TDPCON) from the following sources: Joint Intelligence Center (JIC), Atlantic Intelligence Center, (AIC), Fleet CINC Command Centers, Fleet Ocean Surveillance Information Center (FOSIC), Fleet Ocean Surveillance Information Facility (FOSIF), Shore Targeting Terminal (STT), Cruise Missile Support Activity (CMSA), and Tactical Data Display System (TDDS). Updated data files are sent to afloat units and displayed on MDS, JOTS I/JOTS II, FDDS, and NTCS-A. NTCS-A/JOTS is now known as the Joint Maritime Command Information System (JMCIS). OTCIXS essentially has the same connectivity as TADIXS, except that OTCIXS does not receive data from STT. An exception is submarines; STT data is received by submarines (using TSEC/KG-30 family covered OTCIXS vice the shipboard TSEC/KG-84 covered OTCIXS).
JOTS was originally developed to support OTH-T for Harpoon, Tomahawk, and tactical air strikes. As JMCIS, it has evolved into the primary U.S. Navy and Marine Corps C2 system for tactical decision support, display, and communications ashore and afloat. JMCIS has several installation configurations depending on ship class and/or mission. Equipment nomenclature is AN/USQ-119(V), with 32 variants. The most complex installations are on CV/LCC/LHA/LHD platforms and command centers that provide C2 support to Fleet CINCs, Joint Commanders, numbered fleet commanders, and BG or amphibious commanders. An OTCIXS/TADIXS network diagram is shown in Figure 4.1-47.
Implementation of OTH-T data communication via TADIXS has been accomplished in four phases into a fully automated worldwide system:
lPhase I - OTH-T communications were accomplished using the manually intensive Outlaw Shark Digital Interface Unit (OSDIU).
lPhase II - The ON-143(V)6/USQ Interconnecting Group replaced the OSDIU as the link control device and the OTCIXS satellite network was introduced.
lPhase III - Phase III is characterized by a complex DSD/ON-143(V)6/USQ shore configuration, addition of a second ON-143(V)6/USQ on afloat platforms, and the TADIXS shore-to-ship tactical circuit.
lPhase IV - TADIXS phase IV will provide integrated worldwide connectivity among the OTH-T community, using dedicated circuitry and satellite links, through TADIXS Gateway Facilities (TGF). (Phase III and IV will be discussed later in this lesson topic.)
Figure 4.1-47 OTCIXS/TADIXS Network
The UHF DAMA subsystem was designed to multiplex several users on one 25 kHz satellite channel to add more satellite circuits per channel. Without DAMA, each communications subsystem requires a separate satellite channel. DAMA permits as many as 22 user network requirements to be satisfied on one 25 kHz transponder. DAMA equipment accepts encrypted data streams from independent baseband sources and combines them into one serial data stream. The TD-1271B/U DAMA multiplexer interfaces with UHF SATCOM baseband systems and DAMA compatible AN/WSC-3 transceivers. For DAMA operation, a single master control station is located in each satellite footprint. Each master control station has multiple subscriber units. Each TD-1271B/U can accommodate up to four circuits. Any full duplex DAMA-equipped platform can be designated channel controller to provide emergency backup for shore-based master control stations. To the operator, subsystem operations with DAMA are essentially transparent. With most subsystems, transition to DAMA has taken place so that non-DAMA subscribers can communicate with DAMA subscribers. Subsystems undergoing or planned for conversion to DAMA are SECVOX, CUDIXS/NAVMACS, and TTY.
The control subsystem senses and collects system status information within a satellite footprint within a satellite footprint and on a worldwide scale and controls system resources, based on
demand and the degradation of system capability. The control subsystem is supported by NCTAMs, NCTSs, the USAF Satellite Operations Center, and contractor-operated control facilities. Status data from NCTAMS, NCTS, and USAF Satellite Operations Center is by TTY orderwire. Data status is collected and transmitted to a central location at which control of the system can take place. Status sensing and reporting is provided by:
lCUDIXS link control monitors active/inactive status of subscribers
lInterim FLTSATCOM Spectrum Monitor (IFSM) automatically monitors satellite RF channels (scheduled for replacement by the SATCOM Signal Analyzer, SSA, AN/FSQ-131)
lBit Error Rate monitor, used to monitor Fleet Broadcast from NCTAMS/NCTS
lNAVCOMPARS provides a statistical printout of Fleet Broadcast and CUDIXS message traffic, including disposition
lSatellite remote tracking sites can control status information that is satellite stored, on a schedule or demand basis
TACTICAL RELATED APPLICATIONS (TRAP) BROADCAST SYSTEM
The Tactical Related Applications (TRAP) Broadcast System provides near real-time contact report data to AN/USQ-101(V) Tactical Receive Equipment users. The TRAP system receives contact report data from local and remote collection systems, other TRAP systems UHF broadcast, and other local direct radio broadcast and collection systems. This data is electronically input to a CP-2110(P)/USC Digital Computer where it is validated for correctness and simultaneously output to the TRAP Operator Terminal (TOT) for data archives, and reformed for transmission to the satellite by a AN/WSC-3 and helical Andrew 58622-2 transmit antenna. The signal is received by an AS-2815/SSR-1 and R-2482.
FLEET IMAGERY SUPPORT TERMINAL (FIST)
The FIST system transmits imagery from shore-to-ship, ship-to-shore, ship-to-ship, and shore-to-shore. FIST uses a video camera assembly and closed circuit TV monitor or solid state digitizer to convert imagery or text from film or paper copy into digital signals for transmission over existing secure military communications channels. The system supports the exploitation, transmission, receipt or retrieval, and storage of digital images. Users can manipulate, interpret, and annotate images before and after transmission. FIST capabilities are being replaced and upgraded by the Joint Deployable Intelligence Support System (JDISS). JDISS evolved from the Atlantic Command Deployable Intelligence Support System (LANTDIS). JDISS provides subscribers access to selected portions of the DOD Intelligence Information System (DODIIS) through Consolidated Intelligence Commands Ashore via Ethernet/Disnet 3. Ships receive data from SHF(secure)/INMARSAT(nonsecure) at sea and landline when pierside through the ship's ethernet LAN to a Sun or DTC-2 computer and laser printer. JDISS uses COTS technology, is capable of quality imagery from 2.4 to 9.6 kbps, and is being installed on SHF equipped ships as assets become available.
CURRENT DEVELOPMENTS IN UHF SATCOM SUBSYSTEMS
Increased demands for satellite access, new technological developments, and changes in threat have motivated modifications to existing SATCOM subsystems.
Versa Module Eurocard (VME) Architecture
VME architecture consists of VME cards and a VME bus (chassis) that provides interface with
newer technologies while maintaining compatibility with old technologies. VME architecture is being implemented and developed by program sponsors in the U.S. Navy (e.g., NAVMACS II, TACINTEL II, and TRE equipment). VME design allows multiple microprocessors to be housed in one chassis. The VME chassis contains a standard backplane interface that facilitates the consolidation of data processing and storage. The VME chassis houses VME cards and provides for RED/BLACK partitioning within the chassis. The universal sizes of VME cards support the use of COTS microprocessor boards as well as cards designed for specific subsystems. The functions of VME cards will vary according to functional design requirements (i.e., receiver, signal amplification, signal distribution, deciding, demodulation processing, system controller, and embedded crypto). VME cards are capable of supporting single or multiple functions on a single card, depending on system design requirements.
The TACTINTEL II+ Subsystem is a computer-based message communication system enabling automatic receipt and transmission of SI communications for ashore and afloat users while remaining interoperable with the present TACTINTEL during the transition. A new TACTINTEL equipment suite is being developed to implement the following functions:
lNine different basic message types will be supported with other types to be identified in support of Integrated SI Communications Architecture.
lIn conjunction with the Communication Support System (CSS), under the Copernicus concept, options in configuring baseband interfaces and the use of up to six different communications media.
lA TACINTEL II+ subscriber may participate in up to six TACTINTEL II+ RF nets with automatic message routing between nets.
The TACTINTEL II+ Subsystem will be designed with sufficient flexibility to incorporate future SI communications requirements. TACTINTEL II+ will have the capability to receive, route, and transmit messages automatically on a priority basis. The system will be capable of communications via any required transmission media either net or point-to-point configurations. Communications across any mix of these media will be possible: UHF LOS, UHF satellite, SHF satellite, EHF satellite, HF, or landline. The design of TACINTEL II+ software will permit the automatic switching of data by CSS to different media to provide the most efficient use of communications assets.
High Speed Fleet Broadcast (HSFB)
The HSFB multiplexes individually encrypted broadcast packages generated from multiple user subsystems. These broadcast packages are multiplexed into a 9600 bps aggregate bit stream used in satellite transmission and a separate 1200 bps bit stream for use in HF. The 9600 bps bit
stream will carry a 1200 bps GENSER message broadcast, 1200 bps oceanographic and meteorological broadcast, and a capacity for Fleet CINC requirements. Multiplexing permits multiple user subsystems to share available satellite capacity, and at the same time allows a measure of flexibility in altering subsystem rate in response to varying tactical operating needs and environments. The addition of Forward Error Correction (FEC) to the signal enhances broadcast reliability and quality and provides for the additional bandwidth margin necessary to effectively counter satellite jamming and interference. Mobile platforms receive HSFB via a modified AN/SSR-1A SATCOM receiver and AN/USQ-122(V), which replaces the AN/UCC-1, AN/URA-17, and MD-900/SSR-1.
The phased approach for rehosting the current NAVMACS system on a VME/DTC-2 (Desktop Tactical Computer II) architecture, known as NAVMACS II, is intended to meet growing fleet needs by:
lIncreasing data rates to 4.8, 9.6, and 19.2 kbps
lModernizing the system based on VME technology
lProviding large on-line message storage (up to a 2.4 Gbyte disk)
lIncorporating LAN capabilities
The integration of CUDIXS/NAVMACS II into the DAMA subsystem conserves bandwidth and provides greater flexibility to fleet commanders to maximize allocation of resources. The CUDIXS rehost effort consists of replacing the AN/UYK-20 computer and most of the current peripheral devices while allowing execution of the existing AN/UYK-20 program. This will be accomplished using processor boards installed on a VME chassis, as well as a DTC-2 and associated peripheral devices. Follow-on phases will upgrade the software to enhance operations.
TADIXS A Phase IV
In Phase III, TADIXS A was established as a dedicated network separate from OTCIXS. In Phase IV sophisticated gateways are being installed (replacing interim gateways) to provide enhanced data routing and broadcast capabilities for both OTCIXS and TADIX A. Implementation of Phase IV does not require shipboard procedural changes or equipment modifications. The AN/USQ-64(V)9 TADIXS A Gateway Facility (TGF) will provide integrated worldwide connectivity among the OTH-T community, using both terrestrial and satellite links through a series of computer driven switching nodes. TGFs will be located at NCTAMSs and NAVCOMMSTA Stockton.
In conjunction with the implementation of TADIXS A Phase IV, new OTCIXS firmware is being
installed which will be DAMA compatible. OTCIXS can be operated in a DAMA or non-DAMA configuration; however, all users on a particular net must be similarly configured. Communications between OTCIXS and OTCIXS II users must be accomplished via the TGF.
Mini-DAMA integrates the TD-1271B/U multiplexer and AN/WSC-3 transceiver into a single unit, significantly reducing the size and weight of the system. Mini-DAMA also supports additional communications modes. The capabilities of Mini-DAMA include embedded crypto, satellite link protocols, and eight ports. Three versions are being developed for ship, submarine, and NCTAMSs; major combatants/flag ships; and aircraft. A DAMA controller is being developed and fielded in phases to manage the increasing number of DAMA resources. During the first phase a DAMA Semi-Automatic Controller is being developed that uses the semi-automatic control mode of the TD-1271B/U to control and allocate UHF DAMA Subsystem resources. In the second phase the DAMA Semi-Automatic Controller will be upgraded to support a fully automatic DAMA control mode (Auto-DAMA), in support of CSS and
Copernicus architecture. JCOS policy requires that UHF SATCOM users (except human portable terminal users) to employ DAMA in accessing UHF SATCOM by 1996.
Tactical Data Information Exchange System Broadcast B (TADIX B) Tactical Receive Equipment (TRE)
The purpose of TRE is to support OTH-T for TOMAHAWK cruise missile weapons firing, target changes, and tactical intelligence requirements. The AN/USQ-101(V)3 Tactical Data Information Exchange System Broadcast B (TADIX B) Tactical Receive Equipment (TRE) receives, demodulates, decodes, decrypts, processes, and distributes TADIXS B contact reports to either Tactical Data Processors (TDP), display terminals, and other systems, e.g., NTDS, AEGIS, and TADIXS. The production configuration of TRE hardware will consist of one piece of rack-mounted equipment with all functions except encryption integrated into a single VME box. TRE has the capability for simultaneous operation of up to two TADIXS B broadcast channels and one fleet satellite broadcast channel. TRE has automatic control capabilities to determine
allocation of TRE resources and processing to minimize manual intervention.
SHIPBOARD COMMUNICATION SYSTEMS QUALITY MONITORING
In recent years the volume of shipboard communications has increased dramatically. This rapid expansion has led to the installation of increasingly sophisticated equipment. Factors such as frequency accuracy, DC distortion, intermodulation distortion, and distribution levels are critical to the operation of communication systems. Satisfactory operation of these systems demands precise initial line up and subsequent monitoring to ensure that standards are met and maintained. System degradation is often caused by many small contributing factors which, added together, render the system unusable. Simply monitoring a page printer or listening to the signal is inadequate.
Quality monitoring is the performance of scheduled, logical checks to ensure continuous, optimum performance of shipboard communication systems and in many cases prevent outages
before they occur. Communications personnel often fail to realize the benefits of quality monitoring. They may question the need for quality monitoring, since communications are seemingly adequate. Personnel with this attitude do not perform quality monitoring to gather information about performance trends. Therefore, troubleshooting is less effective and valuable circuit time is lost. Implementation of a monitoring program decreases the workload of communications personnel by allowing system degradation to be detected, isolated, and corrected before outages occur. Additionally, a ship with an aggressive quality monitoring program produces personnel who are thoroughly familiar with the ship's communication systems.
Shipboard Communications Systems Quality Monitoring (NAVTELCOMINST C2796.1) is a manual that provides the necessary information and instructions required to exercise effective quality monitoring of shipboard systems. Extensive instructional material is included. The manual was developed by fleet communicators and is based on proven monitoring techniques that have resulted in an extraordinary improvement in quality and continuity of service. A thorough understanding of the Quality Monitoring Control System (QMCS) is vital to maintaining effective communications. In this regard, the manual is a primary reference for training. Tests prescribed in the manual are based on the use of a QMCS similar to the one depicted in Figure 4.1-48a and 4.1-48b, the AN/SSQ-88. This system is described in more detail in the following paragraphs.
QUALITY MONITORING CONTROL SYSTEM
The QMCS is a multifunction equipment group used as a master monitor for a Radio Communications System (RCS). QMCS permits evaluation of equipment performance to provide failure predictions, identification of interference origins, and equipment fault isolation through manual monitoring of the RCS systems. QMCS is used to determine if the circuit fault or degradation is caused by a failure on the ship and isolate the cause to an equipment or area, if the problem is on board. Monitoring and fault isolation functions are conducted on LF, MF, HF, VHF, and UHF communications equipment operating within the frequency range of 9 kHz to 400 MHz and using any of several modulation techniques.
Signal Monitoring and Analysis
The QMCS enables the measurement and display of selected operational parameters for transmitter and receiver systems in the RCS. The system has access to both baseband and RF signals, which are sampled at points within the transmitter and receiver systems to permit measurement display and realtime analysis of equipment operation without interruption of an active communications channel.
The QMCS is subdivided into three functional areas: measurement and display equipment, generating and modulating equipment, and ancillary equipment. The measurement and display function permits the measurement and display of DC, AF, and RF signals. The generating and modulating function provides a means to generate and modulate signals up to 400 MHz. The
Figure 4.1-48a Typical Shipboard Quality Monitoring System (Page 1)
Figure 4.1-48b Typical Shipboard Quality Monitoring System (Page 2)
ancillary equipment function provides control of the functions that provide the following capabilities:
lMeasuring AF or RF voltage levels and audio dB levels
lAmplifying selected audio signal for local monitoring
lGenerating modulated or unmodulated RF test signal
lMeasuring the frequency of RF signals
lMeasuring and displaying a channel spectrum
lGenerating teletype test signals and analyzing teletype signals
The QMCS consists of one equipment rack, one UHF antenna, and one HF antenna (or HF directional couplers). The equipment rack houses ten electrical assemblies, one rear mounted connector panel, and a stowage drawer. Ensure that your technicians do not remove QMCS test equipment for use in troubleshooting at other locations.
Teletype (TTY) and facsimile (FAX) equipment are used to transmit long messages, charts, maps, and photographs. This section will show you how a basic TTY circuit works, and identify and explain common TTY circuits.
BASIC TTY CIRCUIT
The simplest TTY circuit is the manual telegraph circuit, shown in Figure 4.1-49. This circuit consists of a telegraph key, a source of power, a sounder and a movable sounder armature. If the key is closed, current flows through the circuit and the armature is attracted to the sounder by
Figure 4.1-49 Manual Telegraph Circuit
magnetism. When the key is open, the armature is retracted by a spring. These two electrical conditions of the circuit, "closed" (current flow) and "open" (no current flow), called marking
and spacing respectively, allow us, by means of a code, to transmit intelligence.When the key at
station A is replaced by a transmitting teletypewriter and the sounder arrangement at station B is replaced by a receiving teletypewriter, the basic teletypewriter circuit (loop) shown in Figure
4.1-50 is formed.
Figure 4.1-50 Simple Teletypewriter Circuit
If a teletypewriter signal could be drawn on paper, it would resemble Figure 4.1-51. This is the code combination for the letter R. The shaded areas represent intervals during which the circuit is closed (a mark), and the blank areas represent the intervals during which the circuit is open (a space). There are seven units in the signal, five of which are numbered intelligence units. The first and last units of the signal are start and stop units. The start unit starts the signal and is always a space. The stop unit stops the signal and is always a mark.
Figure 4.1-51 Teletypewriter Mark and Space Signals
Groups of electrical pulses used with telegraph and teletype are referred to as codes. The following is an introduction to the Morse, Baudot, and Automated Information Processing Codes.
In manual telegraphy, the most widely used code is the Morse code. In this code, two distinctive signal elements are used, the dot and the dash. The difference between a dot and a dash is
usually one of time duration, a dash being three times as long in duration as a dot. Each character is made up of a number or combination of dots and dashes, separated from each other by a time interval equal to the duration of one dot. The time interval between the characters for each word is equal to seven dots.
In teletypewriter operation, the code group for each character must be of uniform length. Since the Morse code is an uneven length code, it cannot be used in teletypewriter operation without additional code converters. The five-unit code is universally used in teletypewriter operation. This code is also known as the Baudot code. The Baudot code is a constant length code in which each character consists of five signal elements. Each element may be a mark or a space. A total of 32 signal elements are possible with this arrangement.
Automated Information Processing Code
Through the cooperative effort of representatives of the data processing industry, the
communications industry and the Federal Government, a coded character set was developed and approved as a USA Standard Code for Information Interchange (USASCII). This character set uses a character order more acceptable for data manipulation and processing purposes. The USASCII (or ASCII) is intended to serve as a universal code for input/output purposes and for information interchange in automatic data processing, data transmission and data capture where coded characters are used. The general use of a standard coded character set minimizes
requirements for code conversion and related types of intermediate processing operations when information is exchanged in machine code form throughout the Department of Defense. Current fleet use of ASCII is limited to automated data processing and manipulation, but a considerable effort is being made to use USACII for teletypewriter message transmission. Further information on TTY codes is presented in the MIL-STD-188 Series and in Principles of Telegraphy, 0967-LP-225-0010.
MODES OF OPERATION
There are two basic modes of teletypewriter operation: asynchronous (start-stop) and synchronous. The asynchronous mode is the most commonly used mode of teletype operation. Synchronous operation is used in high speed data systems.
In the asynchronous mode, the receiving device runs for only one character and then stops to wait for the reception of a start signal for the next character. In this mode, any difference in speed between the transmitting and receiving devices can accumulate only during the duration of one character. The penalty for this advantage is that the length of each character must be
increased to include an element to start and stop the receiving device. The Baudot Code is used in this mode.
Synchronous teletypewriter operation, compared to asynchronous operation, does not, in all cases, have to rely on elements of the transmitted character to maintain proper position in relation to the receiving device. External timing signals may be used, allowing the start and stop elements to be discarded. Only the elements necessary to convey a character are transmitted. Synchronous systems have certain advantages over start-stop systems. The amount of time taken to transmit stop and start elements is made available for information transmission rather than for synchronizing purposes, since only the intelligence elements are transmitted. Additionally, a synchronous system has a higher capability to accept distorted signals because it does not depend on start-stop signals.
There are several terms used in referring to teletypewriter modulation rates or signaling speeds. These include words per minute (wpm), baud, and bits per second (bps).
Words Per Minute
Words per minute is used only when speaking in general terms for an approximation of speed, e.g., "100 wpm" means that 100 five-letter words with a space between them can be transmitted in a 60-second period. It is possible to obtain this nominal wpm rate in several systems by varying either the modulation rate or the individual character interval (length). For this reason, the term baud is used.
The word baud is a unit of modulation rate. It is sometimes used to refer to a signal element, but this reference is technically incorrect. Baud rate is the reciprocal of the time in seconds of the shortest unit interval. To find the modulation rate of a signal in baud, you divide the number "1" by the time duration of the shortest unit interval present in the signal. For example, 22 milliseconds (.022) is the time interval of the shortest unit in the five-unit code at 60 words per minute (wpm). To find the number of baud corresponding to 60 wpm, divide 1 by .022 for 45.4 baud. DCS standard speed for teletype operation is 100 wpm or 75 baud.
This term is a contraction of the words "binary digit." In binary signals, a bit is equivalent to a signal element. As a result of the influence of computer and data processing on our language, modulation rate is sometimes expressed as "bits per second" (bps). When it is expressly understood that all signal elements being transmitted are of equal length, the modulation rate expressed in bits per second is the same as rate expressed in baud.
Recall that the two conditions, mark and space, may be represented by any convenient means. The two most commonly used means are neutral operation and polar operation. In the neutral operation, current flow represents the mark and no current flow represents the space. In polar operation, current impulses of one polarity represent the mark and impulses of the opposite polarity and of equal magnitude represent the space. Neutral circuits use the presence or absence of current flow to convey information. These circuits use 60 or 20 milliamperes (mA) as line current. A neutral teletype circuit consists of a transmitting device, a battery source to supply
current, a variable resistor to control the amount of current, a receiving device, and a line for the transmission medium. Polar operation differs from neutral operation in two ways. Information is always present in the system and it is either in a positive or negative condition. A polar teletype circuit consists of the same items as a neutral circuit plus an additional battery source. This battery source is a solid state DC power supply that provides variable current to the teletypes. The reason for having an extra battery source is that the standard polar circuit uses current from the positive side of a battery for marks and current from the negative side of a battery for spaces.
The most significant advantage to polar operation is that, for all practical purposes, it is almost impossible to distort a signal through low line currents, high reactance, or random patching of signal circuits or equipment. Another advantage of polar signaling is that a complete loss of
current (a reading of zero on the milliammeter) indicates line or equipment trouble, whereas the same condition with neutral signaling may indicate only that a steady space is being transmitted. This gives a condition called running open. In this condition, the teletype hammer continually strikes the type box, but there is no printing or type box movement.
BASIC TTY SYSTEMS
When two teletypewriters are wire-connected (looped), the exchange of intelligence between them is direct. When the teletypewriters are not joined by wire, exchange of intelligence is more complex. Direct current mark and space intervals cannot be sent through the air. The gap between the machines must be bridged by a radio transmitter and receiver. The transmitter produces a radio frequency carrier wave to carry the mark and space intelligence. A device such as a keyer is needed to change the DC pulses from the teletype into corresponding mark and space modulation for the carrier wave in the transmitter. A radio receiver and converter change the radio frequency signal back to DC pulses. The navy uses two basic radio-actuated teletype (RATT) systems: the carrier frequency shift system, referred to as radio frequency carrier shift (RFCS) and the tone-modulated system, audio frequency tone shift (AFTS). The RFCS system is
more commonly called frequency shift keying (FSK). Both variations use two discrete radio frequencies to produce one channel of radio teletype, one frequency for the mark signal and the other for the space signal. At any given instant, only one of these frequencies is being emitted by a transmitter.
For FSK systems, the transmitter provides a source of radio-frequency excitation. Figure 4.1-52 illustrates a basic RFCS (FSK) system. A keyer in the transmitter shifts the signal above or below the assigned frequency to correspond with the mark or space required to transmit TTY characters. In both the carrier frequency shift and tone modulated system, all TTY signals pass through the TTY panel that controls the looping current in all the circuits. Looping current is the current supplied by the TTY battery. The TTY panel integrates the tone-modulated and the
Figure 4.1-52 Basic Carrier Frequency Shift (RFCS) System
carrier frequency shift systems. It provides every possible interconnection of available TTY equipment for operational flexibility with the least amount of circuitry and equipment.
Tone modulated systems use amplitude modulation to change DC mark and space impulses into audio electrical impulses. A basic tone modulated system is shown in Figure 4.1-53. Conversion to audio tones is accomplished by an audio oscillator in the tone converter. Rapid varying of the tone, according to the characters transmitted from the TTY equipment, amplitude modulates the carrier wave in the transmitter. The receiver takes the modulated signal and separates the audio from the carrier by the process of detection or demodulation described previously.
Radio frequency carrier shift teletype systems are used in the LF to HF bands for long range communications. To reduce fading and interference problems in these bands, the navy uses two methods of diversity reception. These methods are space diversity and frequency diversity.
In space diversity reception, one signal is transmitted. This signal is received by two or more
receivers. The receiver antennas are separated by a distance greater than one wavelength. Receivers outputs are fed into frequency shift converters that convert the audio frequency shift signals into DC mark and space signals. The DC signals are then fed into a comparator, which
selects the best mark and space signals for the teletypewriter. Because of required spacing
between the receiver antennas, space diversity is mostly limited to shore stations. In frequency
diversity reception, two or more signals carrying the same intelligence are transmitted on different frequencies. The signals are processed by receivers in the same manner as in space diversity reception, operating teletypes with the best of the transmitted signals. This form of frequency diversity is known as RF diversity. Another form of frequency diversity called AF diversity or tone diversity is used with multichannel broadcasts.
A simplex RFCS TTY communication circuit consists of a single channel over which two or more stations may communicate. Each station may transmit and receive, but not simultaneously. On the transmit side, the TTY set keyboard or transmitter distributor applies the DC teletype signals to the communication patch panel where they are patched to the transmitter. The DC mark and space signals shift the frequency of the RF carrier generated by the transmitter as explained previously. On the receive side, the RF frequency-shift signal is demodulated by the receiver, resulting in an audio signal, which shifts between marks and spaces. This audio frequency shift signal is fed to a converter in the converter/comparator group where it is converted into the original DC mark and space signals. The DC mark and space signals are then patched through the communication patch panel to the TTY set.
Figure 4.1-53 Basic Tone Modulated (AFTS) System
RFCS TRANSMIT SYSTEM
The following is a functional description of an RFCS teletype transmit communications system. See Figure 4.1-54.
Two basic models of TTY are the Model 28 family and the AN/UGC-143 series. Several TTY sets have been included in the Model 28 family over the years. Model 28 TTY sets may be send and receive units or receive only units. They may be designed as floor models, table models, or
rack and wall mounted sets. The AN/UGC-143 Navy Standard Teleprinter (NST) is an electronic teleprinter that is being installed in new constructions, new systems/projects requiring teleprinter capabilities, and at navy schools and training facilities. It was designed as a standard replacement for Model 28 TTYs through a process of attrition during modernization and improvement efforts on existing platforms. The NST is available in four configurations: V1 (receive only), V2 (receive only with bulk storage capability), V3 (keyboard send-receive), and V4 (automatic send-recieve). The RFCS transmit system shown in Figure 4.1-54 shows an equipment configuration using a Model 28 floor model set. A receive system will be shown later.
The TTY set receives teletype messages from the line and prints them on page size copy paper. It can also record them on perforated tape. The Model 28 can send messages from either the keyboard or perforated tape, with page size copies provided. Model 28 teletypewriter sets may be composed of the following components, depending on their specific function: a cabinet, a keyboard, a page printer, a typing perforator, a transmitter distributor, a typing reperforator, power distribution panels, and power supply.
The AN/UGC-143A Navy Standard Teleprinter (NST) is fully automated, accepts data in Baudot code or USACII, has bulk storage modules that contain tape drives similar to the AN/USH-26,
can be configured to interface with navy standard personal computers, are fully compatible with
current cryptographic devices, and are capable of supporting paper tape operations. There are
four variations of the AN/UGC-143A(V). The AN/UGC-143A(V)1 is strictly a printer, while the (V)2 has a bulk storage unit and can store messages on magnetic tape for rapid retrieval at a later time. The AN/UGC-143A(V)3 has the capability for message composition, editing, transmitting and receiving. The AN/UGC-143A(V)4 has the features necessary for message composition, editing, receiving, transmitting, and storage.
To provide flexibility in teletype systems, the wiring of all teletypewriters and associated equipment is terminated at jacks in communication patching panels, usually referred to as teletype patch panels. The equipment then is connected electrically in any desired combination by patching cords. The plugs on the cords are inserted into the jacks at the front of the panel. In some instances, commonly used combinations of equipment are permanently wired together within the panel (called normal through). They are wired so that individual pieces of equipment can be "lifted" from the combination, and then used alone or in other combinations. In addition to providing flexibility, teletype panels also furnish a central point for connecting the DC voltage
Figure 4.1-54 RFCS Transmit System
supply into the teletypewriter circuits. Thus, one source of supply can be used for all circuits passing through a particular panel.
Teletype panels SB-1203/UG and SB-1210/UGQ are used for interconnection and transfer of teletypewriter equipment aboard ship. The SB-1203/UG is a general-purpose panel. The SB-1210/UGQ is intended for use with cryptographic devices. The colors red and black are used to identify secure and nonsecure information. Red indicates that secure (classified/encrypted) information is being passed through the panel and black indicates that nonsecure
(unclassified/unencrypted) information is being passed through the panel. In any switching operation between the various plugs and jacks of a teletype panel, the cord plug must be pulled from the looping jack before removing the other plug from the set (machine) jack. Pulling the plug from the set jack first opens the circuits to the channel, causing all teletype messages in the channel to be interrupted. It also produces a dangerous DC voltage on the exposed plug.
Cryptographic equipment is used to encrypt (encode) and decrypt (decode) messages that require security handling. To encode or decode any message, the sending and receiving cryptographic equipment and variable must be compatible.
Remote Transmitter Control
The remote transmitter control unit is mounted close to the teletype keyboard. This unit permits remote control of the transmitter.
The transmitter switchboard SB-863/SRT is used in this system to connect the remote transmitter control unit to the transmitter that is to be used to transmit the signal.
The transmitter transmits the teletype signal. Whoever tunes the transmitter for RFCS operation must be sure that the carrier frequency is properly set to ensure that the correct frequency is obtained at the output of the transmitter.
RFCS RECEIVE SYSTEM
The RFCS receive system (Figure 4.1-55) is used to receive the transmitted signal and translate it back to a usable teletype output.
The antenna filter receives the RF signal from the antenna and filters out unwanted RF signals and passes the desired band of frequencies to the receiver.
The radio receiver receives the RF signal passed from the antenna filter and translates it to an audio signal.
Receiver Transfer Switchboard
The receiver transfer switchboard connects the receiver to any one of the converter units.
Figure 4.1-55 RFCS Receive System
The converter/comparator group is used with receivers in either space or frequency diversity
operation. When diversity operation is not required, each converter can be used separately with a single receiver. The comparator section of the converter/comparator compares the strength of the signals from the receivers in diversity operation. Signals from each converter are fed into a comparator circuit, which compares the signals and allows only the stronger signal to be fed to the communication patching panel for patching to the TTY.
The communication patch panels routes the DC signal to the proper crypto equipment, and routes the decoded teletype signal from the crypto equipment to the selected teletype equipment.
The crypto equipment decodes the signal for printing.
The teletype equipment is used to convert the DC signal received from the communication patch panel to a printed copy of the original transmitted message. The teletype equipment shown contains a page printer only; therefore, it is used for receive only and does not have the capability to transmit.
A simplified block diagram of a half-duplex (send or receive) UHF AFTS system is shown in Figure 4.1-56. A half duplex communication circuit permits unidirectional communication between stations. Communication can be in either direction, but cannot occur simultaneously.
Figure 4.1-56 Half Duplex AFTS Teletype System
On the transmit side, DC signals from the TTY set are fed to the communication patching panel where they are patched to the tone terminal set. The tone terminal set converts the DC signals into audio tone shift signals, which are patched to the transmitter section of the transceiver through the transmitter transfer switchboard. The audio tone shift signals modulate the RF carrier generated by the transmitter. The RF tone modulated signals are then radiated by the antenna. On the receive side, the RF tone modulated signals are received at the antenna and
patched via the multicoupler to the receiver section of the transceiver, where demodulation takes place. The resulting audio tone shift signals are then patched through the receiver transfer switchboard in the tone terminal set, where they are converted back to DC signals and patched through the communication patching panel to the TTY set.
Tone Terminal Set
In tone modulation transmission, the teletypewriter pulses are converted into corresponding audio tones, which amplitude modulate the RF carrier in the transmitter. Conversion to audio tones is done by an audio oscillator in the tone converter. When receiving messages, the tone converter accepts the mark and space tones coming in from an associated receiver and converts the intelligence of the tones into signals suitable to operate a relay in the converter. The make and break contacts of the relay are connected in the local teletypewriter DC loop circuit. This action causes the teletypewriter to print in unison with the mark and space signals from the distant teletypewriter.
TELEGRAPH MULTIPLEXING EQUIPMENT
The number of communications networks in operation throughout any given area is increasing. As a result, all areas of the RF spectrum have become highly congested. To increase the maximum number of intelligible transmissions radio spectrum we use multiplexing. Remember that multiplexing is the simultaneous transmission of a number of intelligible signals in either or both directions using only a single RF carrier.
The AN/UCC-1 Telegraph Terminal Set is used with LF, MF, HF, and UHF radio equipment to demultiplex Fleet Multichannel Broadcast. The AN/UCC-1D is high level or low level capable, while the AN/UCC-1 is high-level capable only. The AN/UCC-1D (Figure 4.1-57) is a frequency division multiplex carrier-telegraph terminal equipment for use with single sideband (SSB) or dual sideband (DSB) radio circuits, AF wire lines or microwave circuits. A complete terminal consists of 16 keyer drawers used for sending and converting DC to audio and 32 converter drawers used for receiving and converting audio to DC. The electrical equipment cabinets shown in Figure 4.1-57 house one control attenuator (right side) and up to a maximum of eight frequency shift keyers or eight frequency shift converters, or any combination of both.
Since the control attenuator, keyers and converters are solid state, integrated circuit plug-in modules, the number of channels may be varied by increasing or decreasing the total number of modules. This terminal can provide up to 16 narrow band channels within a 382 - 3017 Hz
bandwidth. Each frequency shift keyer accepts DC signals from an teletype or encryption device and generates the appropriate AF mark/space frequency-shift output. The individual keyers each contain two oscillators operating on opposite sides of a center frequency. These audio frequency mark/space outputs are referred to as tones; thus keyer number one has a one channel, two-tone output. (Mark and space frequencies may be reversed in local equipment manuals) Each
Figure 4.1-57 AN/UCC-1D
individual channel works in the same way, accepting an input from the TTY set patched to that channel and providing an output audio-frequency mark/space frequency-shifted signal (tone) according to the input. The individual tones are combined at the keyers into a composite tone
package. At the receiving end of the communication link, the telegraph terminal reverses the process performed at the transmitting end and applies the information on each of the channels to the TTY set connected to that channel's converter. In this circuit configuration, each channel has an input from a different TTY. If for some reason (atmospheric conditions, poor reception at a particular frequency, and so forth) this channel fades and the information on it is lost or distorted, the information must be retransmitted. To aid in preventing this, diversity switches that will permit the use of more than one channel for the same intelligence have been provided. In the shipboard multiplexing system consisting of 16 channels, two channels normally carry the same intelligence. This process is called twinning.
The planned system replacement for the AN/UCC-1 and associated equipment (AN/URA-17, MD-900/SSR-1) is the AN/USQ-122(V). This new system will increase data rate and reliability while decreasing equipment size, weight, heat, and power consumption through the use of VME technology. The technical evaluation of this system is in progress and first production is scheduled for early 1995. Note that another system, the AN/USQ-83, was a SPAWAR program to replace the UCC-1 that was never refunded.
LOW LEVEL TELETYPE
In the past, TTY keying signals typically operated at 120 volts 60 mA (milliamperes) line current. Because it was possible for unauthorized electromagnetic detection of this high level signal, a method of operation using nondetectable signals became important. Low-level keying, at much lower voltages of plus or minus 6 volts at 20 microamps, and the use of gold contact points essentially eliminated detectable emissions. This also reduced the safety hazard to personnel working with these circuits. For older ships with TTY equipment that has been modified to operate low level, there are a great many TEMPEST requirements (outlined in MIL-STD-1680) that require your careful observation. TEMPEST was addressed in Module 2.
Facsimile (FAX) is a method for transmitting still images over an electrical communication system. The images, called pictures or copy in facsimile terminology, may be weather maps, photographs, sketches, typewritten, and printed text or handwriting. Military use of FAX is primarily limited to transmission and reception of weather maps. Its tactical uses are limited due
to the length of time between transmission and reception. As EMO, you will encounter a variety of commercial FAX machines that use modems and telephone lines for administrative and logistical purposes (in addition to FIST and JDISS, previously discussed).
PROCEED TO ASSIGNMENT SHEET 4-1-1A IN THE ASSIGNMENT BOOKLET. UPON COMPLETION, TAKE THE ASSIGNMENT BOOKLET TO THE LEARNING CENTER INSTRUCTOR.