FM 24-18: Tactical Single-Channel Radio Communications Techniques


Section I.
General Operating Instructions and SOI

5-1. Effective Operations

The tactical effectiveness of any communications equipment is no greater than the skill of the operators. By the same token, the most efficient communications within a net or command is attained when the operators habitually use the proper procedures in transmitting and receiving messages. This chapter was prepared to assist operators in improving their skills as communicators. It covers the use of the signal operation instructions (SOI), and the techniques that apply to the operation of radiotelegraph (international Morse code), radiotelephone (voice), and radio teletypewriter communications equipment and systems. Single-channel radio can be connected to the tactical telephone system by using net radio interface (NRI) techniques and procedures. They are presented in detail in appendix F.

5-2. Operating Instructions

Instructions pertaining to radio communications are contained in the SOI and in standing operating procedures (SOP).

The SOI provides the organization of stations into nets, assigns call signs, designates net control stations (NCS), and assigns frequencies. It also provides information on changes to alternate frequencies and on authentication. In addition, the security procedures that must be used by radio operators in the command are included in the SOI supplemental instructions.

The SOP governs routine signal operations of a unit. Refer to FM 24-16 for additional information on the SOP and FM 24-35 for SOI.

5-3. Initial Preparation

Before you operate any radio set, get the equipment technical manual (TM) and carefully study the operating instruction. Refer to the panel diagrams, connections diagrams, and the paragraphs covering the description of components during the preliminary starting procedure. Make sure that the proper cables are connected to the proper panel connectors, and that the controls are correctly set. Even the most experienced operators should check their preliminary procedures against the TM references from time to time to insure accuracy and to avoid damage to equipment. Use the operational checklist and the equipment performance checklist to determine what to do to remedy any problems encountered during starting procedures and operation. A time zone chart (app G) and a time conversion table (app H) are included in the back of this manual to assist you in understanding geographical, time zone, and conversion factors you may need during operation of radios and radio nets. Instructions for using DA Form 4158 (Operator's Number Sheet) is contained in appendix I.

5-4. Steps in Operating Radio Sets

Radio sets issued to a unit vary in type according to the communications requirements of the unit. For example, some sets may be completely contained in one assembly, while others may consist of separate components that must be properly connected to assemble a complete radio set. The following steps are generally required in operating a radio set.

Check the Set for Completeness.

Make sure that all the necessary components and accessories are on hand and ready for use. Refer to the equipment basic issue items list in the TM. Never operate the transmitter without the antenna attached.

Inspect the Condition of the Knobs, Dials, Switches, and Controls.

Look for knobs, dials, switches, and controls that are loose on their shafts, bind when being operated, won't operate, or are damaged in any other way. Make corrections where possible or report the faulty condition. Make sure that all knobs and exterior parts are on the set. Immediately report any that are missing.

Check the Condition of Plugs, Receptacles, and Connectors.

Do not attempt to connect the set for operation until you are sure that the plugs and connectors are clean and in good condition and that the receptacles to which they must be connected are also clean and in good condition.

Check the Connections Diagrams.

The connections diagrams in the equipment TM show the type and number of cables required to interconnect the components of the radio set for each type of operation. The radio set may be damaged if cables are connected to the wrong receptacles.

If the connectors don't match, it is possible to physically damage the pins or sleeves of the connector.

If a cable is connected to a receptacle into which it fits but does not belong, it may cause serious electrical damage to the equipment and, in some cases, injury to the operator.

Make Sure of Dial, Switch, and Control Settings.

Some radio sets can be seriously damaged if the switches, dials, and controls are not set to the required initial settings before applying power or making the initial timing adjustments. Before applying power, check the equipment TM to be sure you performed all preliminary starting procedures. Be sure radios installed in vehicles are turned off before starting vehicle engine 80 as to avoid damage to radio equipment.

Follow the Starting Procedure.

The equipment TM covers, in detail, the proper procedure for starting the radio set. If there is a specific sequence for starting the set, it is described in the manual. Perform the operations in the proper sequence.

Apply Power.

After the proper connections are made and all switches are properly set, power may be applied to the set.

Allow the Set to Warm Up.

Radio sets usually require a warm-up period when first applying power in order to stabilize the equipment. In some cases, it is possible to damage a set by attempting to operate a set without allowing a warm-up period. Most sets are protected against such damage, but it is foolish to risk damage to a radio set by trying to put it on the air before it is ready.

Tune to the Desired Frequency (Channel).

Tune the transmitter to the frequency of the desired channel according to the procedures in the equipment TM. Use the methods that are given in the TM to check for correct tuning.

Check the Set for Normal Operation.

While the set is in operation, check the indicators frequently to be sure that the set is operating correctly. If anything unusual occurs during operation, investigate it immediately. When necessary, turn off the power to the set and refer to the operational checklist and the equipment performance checklist in the equipment manual. If the corrections given in the operational checklist and the equipment performance checklist will not correct the trouble, report the condition to the unit electronics maintenance shop. Make sure that the condition of the set and the action taken are properly recorded on the maintenance records.

Use the Proper Procedure to Turn Off the Set.

After operation (or if the set is being turned off because of improper operation) make sure that the controls, switches, and dials are properly set (this may not be required on some radios). Proceed to shut down the components of the set in the sequence specified in the equipment manual. Simple radios may require nothing more than turning the power switch to its off position, but more complex sets may require elaborate shutdown procedures.

5-5. Operating Hints

Use a handset or headset, rather than a loudspeaker, if the incoming signal is weak.

Make sure that the microphone or handset is in good condition. Speak directly into the microphone; speak slowly and distinctly.

Make sure that the vehicle's battery voltage (if radio set is vehicular-mounted) is within the correct range. Keep the engine running to charge the battery.

Move the set or the vehicle, if necessary, to improve reception.

Lack of communications or poor communications may be caused by--

  • Too great a distance between radio sets.

  • Poor choice of location (siting) at one or both ends of the circuit.

  • Terrain--hills or mountains.

  • Noise and interference.

  • Not enough transmitter power.

  • Defective equipment.

  • Improper adjustment of equipment.

  • Ineffective antenna.

  • Improper frequency assignment.

Poorly maintained equipment and improper operation can be just as effective in preventing communications as excessive distance or mountainous terrain. To avoid problems, observe the following precautions at all times:

  • Study the technical manuals for the equipment you are using. They provide complete operating instructions and maintenance procedures.

  • Keep your radio set clean and dry.

  • Handle your radio set carefully.

5-6. The SOI

The SOI is a communications security (COMSEC) aid designed to provide transmission security by limiting and impairing enemy intelligence collection efforts. The SOI does not provide security to the content of messages. The SOI will provide maximum benefits when used with approved cryptographic systems.

The SOI is a series of orders issued for technical control and coordination of a command or activity. It provides guidance needed to ensure the speed, simplicity, and security of communications. The classroom-training SOI is the KTV 1600 ( ) Series for the fictitious 52d Infantry Division (Mech). It serves as a general format and prescribes communications doctrine and techniques which apply to all Army SOI.

The SOI remains the best means of security for nonsecured communications. The procedures and instructions in FM 24-35 implement Department of the Army policy set forth in AR 105-64. FM 24-35 provides the following:

  • A detailed explanation of the centrally produced SOI program.

  • Instructions for the preparation of data required for generation of centrally produced SOI.

  • Instructions for the generation and production of a manually produced SOI.

  • Examples of standardized supplemental instructions for Army SOI.

Section II.
Radiotelegraph Procedures

5-7. Use of Radiotelegraphy

Radiotelegraphy is a system of telecommunications for the transmission of intelligence (or information) by international Morse code. It provides the most reliable radio communications over long distances and under adverse conditions, but requires highly skilled operators. It is used between mobile units and as an emergency substitute for teletypewriter (TTY) communications. Details on radiotelegraph procedures are in ACP 124( ). In addition to normal communication procedures, radiotelegraphy uses PROSIGNs, operating signals, and special abbreviations. Operating signals are listed in ACP 131( ); authorized PROSIGNs and abbreviations are in ACP 124( ). Although CW communications is necessarily slower than voice or teletypewriter communications, it has the advantage of being more readable in the presence of interference and jamming. CW signals can often be read clearly when voice and teletypewriter signals of the same strength are unreadable.

5-8. International Morse Code

Dots and dashes are used in various distinctive combinations to represent the letters of the alphabet, the numerals from O to 9, punctuation, and the procedure signs (prosigns). The dots and dashes of the Morse code are produced by keying a transmitter to transmit short and long signals. The dash is three times the length of the dot. The combination of dots and dashes that are used for a letter are spaced from each other by a period of time equal to the length of one dot. Letters are spaced from each other by a period of time equal to three dots and words are spaced by a period of time equal to seven dots.

5-9. Procedure Signs

Procedure signs (prosigns) are used on radiotelegraph and radio teletypewriter circuits to convey information, requests, orders, and instructions in a condensed standardized form. Prosigns represent single words or phrases in order to minimize transmitting time. Certain letters are transmitted "run together"--that is, without a space between the letters--and represent a phrase other than the letters. They are overscored (written with a line drawn over the top of them). For example, is transmitted as if it were a single letter, not as two letters, and means "end-of-transmission."

Authorized PROSIGNs and their meanings are listed in table 5-1.

Table 5-1. Procedure Signs

5-10. Operating Signals

Operating signals are three-letter signals starting with the letter Q or the letter Z. They are used by CW operators and radio teletypewriter operators to expedite communications. Each Q-signal or Z-signal conveys the meaning of a number or words and, at times, a complete message. For example, ZFG means "This message is an exact duplicate of a message previously transmitted." Information on authorization of Q- and Z-signals is in ACP 131( ).

ACP 131( ) lists the meanings of Q- and Z-signals and provides instructions for their use. If it is not possible to provide each operator with a copy of ACP 131( ), lists of commonly used signals should be prepared and provided to each operator. In no case should the operator be required to memorize all of the operating signals.

Operating signals are considered to be plain language, and they must be encrypted when used as a part of an encrypted message. They are an aid to communications security, since they are brief; but their meanings are common knowledge to many nations.

5-11. Transmission Techniques and Transmission Speeds

Each character shall be transmitted clearly and distinctly. The speed of transmission shall be governed by the prevailing conditions and the ability of the receiving operator.

Accuracy in transmission is far more important than speed. The difference in time required to send a message at 18 words per minute and the time required to transmit it at 25 words per minute is slight. Even this slight gain in time may be nullified by any added time required for repetitions.

The speed at which the receiving operator can copy without having to obtain repetitions is the speed at which the transmitting operator will transmit. When transmitting to more than one station in a net, the governing speed of the transmitting operator is that of the slowest receiving operator.

The speed of transmitting headings on manually operated circuits should be slower than the speed of transmission of texts.

Speed of transmission on automatic circuits is governed by traffic conditions and the reliable capacity of the equipment.

If necessary during specific periods, the net control station can prescribe the speed of transmission on a circuit or set certain qualifications which operators must meet.

When authorized by the net control station, speed keys may be employed on manually operated circuits if traffic conditions warrant and operator abilities permit.

Section III.
Radiotelephone and Radio
Teletypewriter Procedures

5-12. Radiotelephony

Radiotelephony is a system of telecommunications that is normally used for short-range tactical communications and between mobile and air units. It provides rapid, person-to-person communications in highly mobile situations. However, radio transmissions are subject to enemy interference and afford little or no security to messages if a security device is not used with the radio set. Therefore, basic rules essential to transmission security are strictly enforced on all military radiotelephone circuits. Details on radiotelephone procedures are in ACP 125( ). Just as radiotelegraphy makes use of PROSIGNs and operating signals, radiotelephony uses procedure words (PROWORDs) and procedure phrases. Authorized PROWORDs are covered later in this section.

Transmission Security.

The following basic rules are essential to transmission security and will be strictly enforced on all military radiotelephone circuits.

No transmission will be made if it is not authorized by the proper authority.

The following practices are specifically forbidden:

  • Violation of radio silence.

  • Unofficial conversation between operators.

  • Transmission on a directed net without permission.

  • Excessive tuning and testing.

  • Transmission of the operator's personal sign or name.

  • Unauthorized use of plain language.

  • Use of other than authorized PROWORDs.

  • Unauthorized use of plain language in place of applicable PROWORDs or operating signals.

  • Association of classified call signs and address groups with unclassified call signs.

  • Profane, indecent, or obscene language.

Call Signs.

Call signs are used in radio communications to identify a communications facility, a command, an authority, or a unit. There are two forms of call signs: complete call signs and abbreviated call signs.

Complete call signs consist of a letter - number - letter combination and a suffix and are used when--

  • Entering a net in which you do not normally operate.

  • When so requested by the NCS or another station in the net.

Abbreviated call signs are used at all other times.


Complete Call Sign______________________A2D28
Abbreviated Call Sign_____________________D28

If no confusion exists as to which operators are on the radio net, no call signs need be used.

5-13. Pronunciation of Letters and Numerals

To avoid confusion and errors during voice transmission, special techniques have been developed for pronouncing letters and numerals. These special techniques resulted in the phonetic alphabet and phonetic numerals.

The phonetic alphabet is used by the operator to spell difficult words and thereby prevent misunderstanding on the part of the receiving operator. The words of the phonetic alphabet, which is a word alphabet and not a code, are pronounced as shown in table 5-2. The underscored portion indicates the syllable or syllables to be emphasized.

The phonetic alphabet is also used for the transmission of encrypted messages. For example, the cipher group CMVVX is spoken "CHARLIE MIKE VICTOR VICTOR XRAY."

Numbers are pronounced as shown in table 5-3.

Table 5-2. Phonetic Alphabet

Table 5-3. Number Pronunciation Guide

Numbers are spoken digit by digit, except that exact multiples of thousands may be spoken as such. For example, 84 is "AIT FOW ER," 2,500 is "TOO FIFE ZE RO ZE RO," and 16,000 is "WUN SIX TOUSAND."

The date-time group is always spoken digit by digit, followed by the time zone indication. For example, 291205Z is "TOO NIN-ER WUN TOO ZE-RO FIFE ZOO-LOO."

Map coordinates and call sign suffixes also are spoken digit by digit.

5-14. Procedure Words

To keep voice transmission as short and clear as possible, radio operators use procedure words (PROWORDs) to take the place of long sentences. The PROWORDs and their meanings are listed in table 5-4.

5-15. Radio Teletypewriter

Radio teletypewriter communications is a system of telecommunications for transmitting information over radio (FSK mode) using direct action of a teletypewriter keyboard, perforated tape, or from electronic memory storage. This same information is received in the form of page copy, perforated tape, or both.

A big advantage of field radio teletypewriter operations is that through the use of one mobile radio teletypewriter set you have available all three modes of radio telecommunications systems--radiotelegraph, radiotelephone, and radio teletypewriter. Transmission is possible over distances up to several thousand miles.

Radio teletypewriter operators must be highly trained. Those operators possessing the additional skill identifier (ASI) for international Morse code must maintain their proficiency in radio telegraph operations. Radio telegraph operators must use IMC when the quality of the circuit drops below that required for radio teletypewriter communications.

Message format and the procedure for handling messages by radio teletypewriter are the same as prescribed for manual teletypewriter operations listed in ACP 126( ).

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