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CRITICAL TASKS: 01-5878.04-0005,
01-5778.07-0003, 01-5778.07-0007



In this lesson you will learn about the newest generation of tactical radio equipment (SINCGARS and IHFR) including equipment capabilities and characteristics, equipment selection and configuration, and the role of this equipment within the Army Tactical Command and Control Systems.



  1. Describe the purpose of combat net radio (CNR) in support of Army Tactical Command and Control Systems.

  2. Describe the purposes and capabilities of SINCGARS and IHFR.

  3. Identify the planning/management factors for single-channel radios.

  4. Describe CNR nets and equipment placements within signal organization command posts (CPs).


You will be given information from this lesson.


To demonstrate competency of the terminal learning objective, you must achieve a minimum score of 70% on the subcourse examination.


The material contained in this lesson was derived from the following publication: FM 11-32.


Advances in electronic technology have brought about many changes in the way we view communications in a very short time. New products are constantly being developed to enhance the various aspects of radio communications. In addition, we have made great progress in effectively integrating electronic counter-countermeasures technologies into radio equipment. This makes the vital command and control (C2) functions of radio more survivable in an RF hostile environment. The introduction of frequency hopping (FH) equipment allows us to transmit messages over a spread RF spectrum. This ability degrades the enemy forces' abilities to locate, monitor, jam, or destroy friendly radio systems. As these new technologies become field operational, they are replacing the older single-channel radio systems. The new systems provide the maneuver force commander with a reliable multifaceted C2 communications system. The new radio equipment gives him a combination of HF, VHF, and UHF communications capabilities. This provides him with three separate systems, each capable of using a different transmission path to pass the same information. The result is that the probability of any one system operating under any adverse RF conditions is greatly enhanced, directly enhancing force C2 functions.

1. Combat Net Radio.

The new radio systems being brought into use demand a new structure for communications. The combat net radio (CNR) network was designed to integrate and take full advantage of the enhancements in modern radio technology in support of C2. The CNR net is based around three basic radio systems, each with its own distinctive capabilities and characteristics. The three systems are: improved high frequency radio, Single-Channel Ground and Airborne Radio System, and single-channel tactical satellite (TACSAT). This subcourse deals with IHFR and SINCGARS systems. Subcourse SS 0060 explains the TACSAT system, however, review of SS 0060 is not required for completion of this subcourse.

2. The Role of CNR.

The primary role of the CNR network is voice communications for C2. It also performs a secondary role as a backup for data transmission when requirements exceed the capacity of the Army Data Distribution System or Mobile Subscriber Equipment services. In CNR networks, voice C2 information has priority except when SINCGARS is used with the Tactical Fire Direction System or Advanced Field Artillery Tactical Data System.

3. CNR Network Structure.

The CNR system generally establishes three categories of VHF-FM networks. They are C2, Administrative/Logistics, and Intelligence. The C2 network (the primary CNR net) is subdivided into functional areas of maneuver, fire support, aviation, air defense artillery (ADA), and engineers. Figure 5-1 shows the typical network structure for the division or brigade level.

Figure 5-1. Radio net structure
Figure 5-1. Radio net structure


SINCGARS equipment is replacing the AN/PRC-77 and AN/VRC-12 series equipment currently in use. SINCGARS is a modular system, allowing components of one piece of equipment to serve as replacements for another. This feature provides increased reliability of communications overall. SINCGARS has two basic modes of communication: single-channel or FH. In the single-channel mode, it can communicate with any of the older VHF-FM equipment currently in use. In this mode, SINCGARS equipment can hold up to eight single-channel frequencies. The SOP will generally specify what frequencies will be stored.

When you shift the SINCGARS equipment to FH mode, it shifts operating frequencies about 100 times per second in the 30-87.975 MHz range. The audio signal is then modulated on the shifting carrier to produce an output signal that moves about the VHF spectrum. This "hopping" of the frequency makes the signal very difficult for enemy forces to detect, locate, or jam. If the changing of frequencies was completely random, there would be no way for two sets to communicate. The receiving set has to change frequencies in the same manner as the transmitter. To accomplish this synchronous frequency hopping, the SINCGARS equipment stores up to six separate hopsets. Each hopset is a code that tells the unit how and when to change frequencies in a repeating pattern.

In order to establish communications, two stations would make contact in single-channel mode and then switch to their designated hopset to conduct FH operations. As with the single-channel presets, the SOP defines the hopsets to be stored. One additional feature of SINCGARS equipment that makes it better than its predecessors is the ability to control output power of the unit. You can change power settings to transmit from 300 meters to 35 km (22 mi). This feature is advantageous both in field applications where detection is undesirable and in command post applications where many radios are operated simultaneously. You should always take care to operate at the minimum power required to ensure effective communications. The following paragraphs will describe the components and some of the various configurations of SINCGARS equipment.

  1. Receiver-Transmitters RT-1523 and RT-1439. All ground-based SINCGARS configurations use either the RT-1523 or the RT-1439 as the basic component. Both units transmit and receive between 30 and 87.975 MHz. Both units are capable of FM, FSK, FH, and digital data input modes of operation. The RT-1523 has an internal integrated communications security (ICON) module built into it. The RT-1439 is a non-ICON radio but it can be secured using the KY-57 VINSON secure device. As stated previously, both units can store up to eight single-channel presets and six hopsets. Two of the eight single channel frequencies are the manual and cue frequencies. The manual frequency is the frequency that stations will establish communications on to activate the network. After communications have been established, stations will shift to the designated frequency hopset. Once the network has been established, a station desiring to enter the net will contact the net on its cue frequency. The net control station must then shift to the cue frequency to communicate with the new station and inform him of the frequency hopset parameters to use to join the net. Figure 5-2 shows the receiver-transmitter and its supporting components in a typical mobile installation.

Figure 5-2. Radio set components
Figure 5-2. Radio set components

  1. Manpack Radio AN/PRC-119. This SINCGARS manpack radio is replacing the AN/PRC-25 and AN/PRC-77 manpack radios currently in use. The unit consists of one receiver-transmitter and a battery pack. If you use the RT-1439 then you must also use the VINSON security device. Figure 5-3 shows the various parts of the PRC-119 configuration.

Figure 5-3. Manpack radio AN/PRC-119
Figure 5-3. Manpack radio AN/PRC-119

  1. Vehicular Short-Range Radio AN/VRC-87. The VRC-87 is replacing the AN/GRC-53 and AN/GRC-64 as the short-range vehicular tactical radio. This unit is essentially the same as the PRC-119 with extra cabling and no battery.

  2. Dismountable Short-Range Radio AN/VRC-88. The VRC-88 adds the components to the VRC-87 necessary to make it a portable unit. This unit is replacing the AN/GRC-125 and AN/GRC-160.

  3. Vehicular Long-Range/Short-Range Radio AN/VRC-89. The VRC-89 adds a second receiver-transmitter and a power amplifier to the VRC-87 configuration. This configuration allows the unit to monitor one net while communicating in another. This configuration is replacing the AN/VRC-12 and AN/VRC-47 configurations. Figure 5-4 shows the SINCGARS equipment in the VRC-89 configuration.

Figure 5-4. Vehicular long-range/short-range radio AN/VRC-89
Figure 5-4. Vehicular long-range/short-range radio AN/VRC-89

  1. Vehicular Long-Range Radio AN/VRC-90. The VRC-90 is essentially a VRC-87 with a power amplifier added for long-range capability. The VRC-90 is replacing the AN/VRC-43 and AN/VRC-46.

  2. Vehicular Short-Range/Long-Range dismountable radio AN/VRC-91. This unit is essentially identical to the VRC-89 except that it adds the necessary components to be operated as a manpack radio, providing manpack long-range capability. The VRC-91 does not replace any current equipment. The closest current configuration would be an AN/PRC-77 and either a VRC-43 or a VRC-46 in the same vehicle.

  1. Vehicular Dual Long-Range/Retransmission Radio AN/VRC-92. The VRC-92 replaces the AN/VRC-45 and AN/VRC-49 as the vehicular station capable of acting as a retransmission station. It is the same as the AN/VRC-89 with an additional power amplifier. This configuration provides high-power capability for both receiver-transmitters.

  1. Intravehicular Control Unit IVRCU C-11291. This device allows the operator to control up to three separate radios in armored vehicles. It can control all radio functions and can be used with ICOM and non-ICOM radios. The unit can also be set up so that three different operators can control the radio from their respective positions in the vehicle.

  2. SINCGARS Remote Control Unit (SRCU). This device allows you to remotely operate your radio from up to 4 km (2.4 mi) away. The SRCU allows for secure remote operation including the control lines from the radio to the SRCU. It also provides intercom facilities between the radio and the remote site. All radio functions can be controlled remotely with the SRCU. The AN/GRA-39 can also be used to remotely control SINCGARS radios, but it only allows remote keying of the radio set.

  3. Data Fill Devices MX-10579 and MX-18290. Data fill devices contain hopset and transmission security key (TSK) information for use with SINCGARS in FH mode. The TSK information actually tells the unit how to control the frequency hopping sequence. The MX-10579 holds up to 13 hopsets and 2 TSKs and you must use it with non-ICOM radios only. The MX-18290 holds 13 hopsets and 6 TSKs. Currently, you must have two fill devices to operate a secure SINCGARS radio in FH mode. One fill device is needed to load the radio and the second loads the security device (VINSON or ICOM).

  1. VINSON and ICOM Secure Devices. Secure devices provide the means for secure voice communications between remote stations. The ICOM device is built into the ICOM transmitter. It contains one traffic encryption key (TEK) for each hopset. This means that in addition to frequency changing constantly, the information being passed is also encrypted. The VINSON device is an external device and is used with the non-ICOM radios. It has six preset positions, five for TEKs and one for a key encryption key (KEK). The five TEKs used with the radio allow secure operations in up to five different networks at one time. The KEK allows the VINSON device to be loaded by over-the-air (radio transmission) fill. In other words, several field units could carry VINSON devices and not carry any encryption codes. A transmitter located at a safe location could transmit the TEK information to all field units simultaneously. Thus, the units could set up secure networks without carrying any cryptographic codes with them. Both the VINSON device and the ICOM radio set are considered cryptographic material and should be destroyed if a unit possessing them is overrun.

5. IHFR.

The IHFR system is another new-technology modular system being introduced into operation. The system is designed to replace the AN/PRC-70, AN/PRC-74, and AN/GRC-106 systems currently in operation. The following paragraphs describe the major components and configurations for IHFR equipment.

  1. Receiver-Transmitter RT-1209. The heart of the IHFR system, RT-1209 is an AM/SSB (USB or LSB) radio set. It is compatible with the AM/SSB sets currently in use but is not directly compatible with the older AM/DSB equipment. An experienced DSB operator may still be able to pick up the SSB transmissions however. The RT-1209 operates between 2 and 30 MHz in the HF band.

  2. Manpack Radio AN/PRC-104A. This portable unit will replace the AN/PRC-70 and AN/PRC-74 radios currently in use. It consists of a basic receiver-transmitter and support equipment. The PRC-104A also uses a tunable antenna and has an automatic antenna tuning feature built into the unit.

  3. Low-Power Vehicular/Manpack Radio AN/GRC-213. Shown in figure 5-5, the GRC-213 combines the features of the older GRC-106 into a unit capable of vehicular or manpack use. Depending on the application, different amplifiers, power supplies, and antennas are attached. An important note on these radio sets is that your operators should always avoid excessive keying of the radio. The low-power IHFR radio has a maximum key down time of one minute and a ratio of one minute transmit to nine minutes receive. Exceeding this key down time can damage the radio set.

Figure 5-5. Radio set AN/GRC-213
Figure 5-5. Radio set AN/GRC-213

  1. High-Power Vehicle Radio AN/GRC-193A. The GRC-193A is a basic RT-1209 with a high-power supply and support components. Figure 5-6 illustrates this configuration. The AN/GRC-193A is replacing the AN/GRC-106.

Figure 5-6. Radio set AN/GRC-193A
Figure 5-6. Radio set AN/GRC-193A

6. Siting Considerations.

A CP in a modern battlefield scenario is a central clearing house for information. Many radio sets are operated in a relatively small geographical area. It stands to reason that these various radios will, from time to time, interfere with each other. The various combinations of SINCGARS, IHFR, and Mobile Subscriber Radiotelephone Terminal/Radio Access Unit (MSRT/RAU) equipment produce interference in three basic categories: IHFR to IHFR, SINCGARS to SINCGARS, and SINCGARS to MSRT/RAU. Since IHFR operates in a different frequency band, it is not likely that you will experience interference between it and either of the other two systems. Interference you experience as a result of having co-located radio sets is called cosite interference. There are three basic methods of controlling communications and managing the CP so that cosite interference is minimized. They are spectrum sharing, antenna separation, and network time sharing. The following paragraphs describe each of these methods.

  1. Spectrum Sharing. The Battlefield Spectrum Manager (BSM) is responsible for providing spectrum sharing to minimize cosite interference. In the case of SINCGARS and MSRT/RAU systems, he must ensure that different hopsets operate on different frequencies and that MSRT/RAU frequencies are not included in any SINCGARS hopset. The particular pattern for spectrum sharing depends on the transmission requirements and the RF conditions that exist at the CP. The BSM has overall responsibility to correct any interference problems that arise from co-located radio sets.

  2. Antenna Separation and Network Time Sharing. Each command should decide on an individual basis when to use antenna separation and time sharing as a means of minimizing cosite interference. In a strategic CP that is fixed in one position, it may be possible to plan out antenna separation schemes and remotely locate the antennas that are most likely to interfere with each other. On the other hand, in a tactical CP that moves fairly often, it may not be feasible to remotely locate antennas due to the time required to set up all the equipment. In the latter case you may want to use just network time sharing, having the frequencies that are close enough to produce interference operate at different times of day. The preferred method of reducing cosite interference is to combine some form of antenna separation and network time sharing.

7. Summary.

In this lesson you have learned some of the basic information about two of the newest tactical radio systems the Army will introduce into field operations. You have also learned about the net structure and some of the basic problems you may encounter using this equipment.


Lesson 5 Practice Exercise:
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Page last modified: 27-04-2005 07:38:03 Zulu