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Military

Chapter 3

AM Radio Operations

3-1. General

Equipment shortages or differences may cause serious problems. The problems could result in having only one or two radio sets to pass all the traffic normally passed by six or more sets. AM radios, combined with ancillary equipment, can pass traffic in either of three modes: voice, RATT, or CW. This chapter addresses solutions to the problems caused by equipment shortages or differences.

3-2. Reduced Assets

Following are alternatives for operating with reduced assets:

a. Operate one AM radio in several nets using an established time schedule. Select the most important net to monitor and operate in. Enter the other nets only when necessary to pass traffic. Enter the other nets at preplanned times or notify the other stations by telephone or FM radio at unscheduled times. The schedule should change every day and be randomly generated to preclude the enemy from analyzing your traffic pattern.

b. Preplan all messages by using brevity lists and codes to shorten the time spent on the air.

c. Use the TCC's off-line teletypewriters to prepare teletypewriter tapes prior to submitting traffic to the RATT operator for transmission. This reduces the RATT operator's burden and saves transmission time.

d. Use FDX operation on equipment which has FDX capability. Much more traffic can be passed over FDX circuits than over half-duplex circuits, thereby reducing time required for passing traffic.

e. Transmit low priority traffic over alternate means, such as messenger or multichannel radio, if they are available.

f. Use one radio, if possible, for several individuals, staff sections, or units.

g. Establish a wire link with a distant station using the existing teletypewriter and secure device along with a telegraph terminal TH-5/TG or TH-22/TG when the radio or modem of a RATT system is defective. Speech-plus can also be provided using this technique by using telegraph-telephone terminal AN/TCC-14 or AN/TCC-29.

h. Use error correcting burst communication devices, such as the AN/PSC-2, if available, to cut down on air time and errors.

3-3. Equipment Considerations

a. When different types of AM radios must work together in the same net, the SOI must include proper frequency assignments compatible to each type of radio equipment. All nets using two or more different AM radios are restricted to certain frequency ranges or modes of operation. (The various technical characteristics of all the AM radios currently in the Army inventory will be covered later in this chapter.) Frequency and mode assignments must be coordinated prior to joint operations when units with different AM radios may be involved together.

b. When planning nets, radio planning ranges must be considered. Certain AM radios have much more power than others, so planning ranges must be based on the least powerful radio's capabilities. Related to the distance factor is the type and polarization of antennas. Antennas must be properly polarized and correctly oriented. For extended ranges, a half-wave doublet antenna, such as the AN/GRA-50, should be used whenever time and terrain permit.

c. By obtaining prior approval, various civilian radios with AM, CW, and SSB capabilities can be used. When using civilian radio equipment, proper military procedures will be used. For operation of ranges between 0 and 450 km, the near vertical incidence skyware technique described in FM 24-18, Appendix N, should be used. This will allow skip zone free omnidirectional communications at low power under all conditions.

NOTE: Under no circumstances will citizen's band procedures be used.

3-4. AM Radio Security

Some military AM radios may be secured in the voice mode using the KY-65. Most AM radios can be secured for RATT operation using TSEC/KW-7 or TSEC/KG-84A security devices. Some of the older radios have not been modified to accept the KW-7 at this time but can be altered to accept it as required. If time and situation permit, ensure that all your radios have been modified to accept security devices. When operating a nonsecured radio in voice or CW modes, codes or off-line encryption methods must be used.

NOTE: The KG-84A will only operate with AN/GRC-142/122 RATT sets equipped with MK-2488 installation kits.

3-5. Netting Old and New Equipment

Most AC use the newer families of SSB radios, whereas RC have a combination of the older AM and the newer SSB equipment. The new equipment can work with the older equipment, but it takes just a little extra care to make it work correctly. The planner needs to know the technical characteristics of all the radio sets involved to plan the communications network properly. Table 3-1 is a comparison of technical characteristics of the AM radios in the Army inventory.

a. The most important technical characteristics to consider when netting two different radios are the type of tuning and type of emission.

(1) Table 3-1 shows that the older radios have continuous tuning whereas the newer radios have detent tuning. The difference between these two is that detent-tuned radios can tune only to certain frequencies and cannot tune to the in-between frequencies to which the continuous-tuned radios can tune. The continuous-tuned radios must tune to the detent-tuned radios. This includes the radio systems used by other military services (such as Marines, Navy, Air Force) . Continuous-tuned radios operate approximately 1.5 kHz below the detent-tuned radio's frequency. The NCS should have a new series radio set to which all radios can tune. If the NCS does not have a new series radio set, the operator should direct a station with a new series radio to provide the signal to which all others tune. Check Table 3-2 for compatible frequency ranges.

(2) Emission types must match. In the CW mode, the type of emission for both old and new series radio sets is the same. In the FSK mode, the type of emission is the same, but the way the carrier shifts is different -a problem that can be overcome. The type of emission for voice, however, is different. The old series equipment uses DSB while the new series equipment uses SSB and compatible AM. Only the compatible AM mode of the new series radio can be used with the older equipment. SSB cannot be used to communicate with the older series equipment.

b. The difference in frequency ranges must also be considered when operating old and new series radio sets together. The old series radio sets have a transmitting frequency range between 1.5 to 20 MHz, and a receiving frequency range between 0.5 to 32 MHz. The new series radio sets have a frequency range for transmitting and receiving from 2.0 to 29.999 MHz. When operating between the old and the new series radios, the operating frequency must be within 2.0 to 20 MHz.

c. The most commonly used old series RATT sets are the AN/GRC-46 and the AN/GRC-26D. They are used by RC. The most commonly used new series RATT sets are the AN/GRC-142 and the AN/GRC-122. They are used by both RC and active Army. Older generation radio sets may be used by other services, and may be encountered during joint operations. Characteristics of both old and new series equipment are listed in Table 3-3.

3-6. Interoperability Procedures

The rules for netting old and new series radio sets for voice, CW, and RATT operations are given below.

a. Voice operations.

(1) For new series radio sets An/GRC-142/122

    • Tune for normal voice operation.
    • Change the SERVICE SELECTOR switch on the RT-662 or RT-834 from the AM position.
    • Conduct normal voice operation.

(2) For old series radio sets AN/GRC-46 and AN/GRC-26D--

    • Tune equipment as usual for voice operation.
    • Rotate the CONTINUOUS TUNING dial for clearest voice reception while receiving voice signal from a station in the net using a new series radio set.
    • Realign transmitter to receiver.
    • Conduct normal voice operation.

(3) For voice tuning procedures of old and new radios, see Table 3-4.

b. CW operations.

(1) For new series radio sets AN/GRC-142/122--

    • Tune radio set for normal operation.
    • Change the SERVICE SELECTOR switch on the RT-662 or RT-834 to the CW position.

NOTE: In the CW mode, the transmitted RF signal is 2 kHz higher than the frequency indicated on the receiver-transmitter MC and KC controls.

    • Lower the operating frequency by 2 kHz on the RT-834/662. Key radio set with CW keying device and adjust BFO control left or right for comfortable listening tone.
    • Conduct normal CW operation..

(2) For old series radio sets AN/GRC-46 and AN/GRC-26D--

    • Tune radio sets for normal CW operations.
    • Rotate the CONTINUOUS TUNING dial on the receiver until a clear CW signal is heard while receiving a CW signal from a station in the net using a new series radio set.
    • Realign transmitter to receiver.
    • Conduct normal CW operations.

(3) For CW tuning procedures of old and new radios, see Table 3-5.

c. RATT operations.

NOTE: Other than netting with the continuous tuning dial for voice and CW operations, the operator of the new series radio set was the only one that had to make changes in the normal tuning procedures of his radio set. For RATT operations, both the operator of the old series and the new series radio sets must make changes from the normal tuning procedures. The primary reason is the position of the mark and space signals in relation to the carriers of the two types of equipment. Old series radio sets transmit the mark signal above the carrier and the space signal below the carrier. The new series radio sets transmit the mark signal below the carrier and the space signal above the carrier.

(1) For new series RATT sets AN/GRC-142/122, VSC-2, and VSC-3--

    • Tune RATT equipment as usual for normal RATT mode of operation (Table 3-6).
    • Change the SERVICE SELECTOR switch on the RT-662 or RT-834 to the FSK position.
    • Change the RECEIVE switch on modem MD-522 from normal to reverse.
    • Change the MODE SELECTOR switch on MD-522 to 850 Hz.
    • Adjust the BFO on the MD-522 for reverse scope alignment when receiving a teletypewriter signal. If necessary, adjust the frequency vernier to assist BFO scope alignment when tuning the receiver to the receive signal.
    • Conduct normal RATT operation.

    NOTE: When receiving a teletypewriter signal from like equipment (new series radio to new series radio), the RECEIVE switch must go back to NORMAL in order to receive.

    (2) For old series RATT set AN/GRC-46, VSC-1, and VRC-29--

      • Tune RATT equipment as usual for normal RATT mode of operation (Table 3-6).
      • Change the SERVICE switch on converter CV-278 from normal to reverse.
      • Adjust receiver R-392 to the tuning signal of the AN/GRC-142/122, VSC-2, or VSC-3. Adjust until a mark 40 signal to the right of 0 is received on converter CV-278.
      • Realign transmitter to receiver.
      • Conduct normal RATT operation.

    (3) For old series RATT set AN/GRC-26D--

      • Tune RATT equipment as usual for normal RATT mode of operation (Table 3-7).
      • Change the MARK HOLD switch on converter CV-116 from XTAL (left) (NORM) position to the XTAL (right) (REV) position.
      • Adjust receiver R-390 to the tuning signal of the AN/GRC-142/122, VSC-2, or VSC-3. Adjust until a mark 50 signal to the right of 0 is received.
      • Realign transmitter to receiver.
      • Conduct normal RATT operation.



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