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Radiotelephony procedure (also on-air protocol and voice procedure) includes various techniques used to clarify, simplify and standardize spoken communications over two-way radios, in use by the armed forces, in civil aviation, police and fire dispatching systems, citizens' band radio (CB), and amateur radio.

Voice procedure communications are intended to maximize clarity of spoken communication and reduce errors in the verbal message by use of an accepted nomenclature. It consists of a signalling protocol such as the use of abbreviated codes like the CB radio ten-code, Q codes in amateur radio and aviation, police codes, etc., and jargon.

Some elements of voice procedure are understood across many applications, but significant variations exist. The armed forces of the NATO countries have similar procedures in order to make cooperation easier.

The impacts of having radio operators who are not well-trained in standard procedures can cause significant operational problems and delays, as exemplified by one case of amateur radio operators during Hurricane Katrina, in which:

...many of the operators who were deployed had excellent go-kits and technical ability, but were seriously wanting in traffic handling skill. In one case it took almost 15 minutes to pass one 25 word message.^[1]

Introduction

Radiotelephony procedures encompass international regulations, official procedures, technical standards, and commonly understood conventions intended to ensure efficient, reliable, and inter-operable communications via all modes of radio communications. The most well-developed and public procedures are contained in the Combined Communications Electronics Board's Allied Communications Procedure ACP 125(G): Communications Instructions Radiotelephone Procedures.^[2]

These procedures consist of many different components. The three most important ones are:

1. Voice procedures—what to say^[3]
2. Speech technique—how to say it^[3]
3. Microphone technique—how to say it into a microphone

These procedures have been developed, tested under the most difficult of conditions, then revised to implement the lessons learned, many times since the early 1900s^{[clarification needed]}. According to ACP 125(G)^[2] and the Virginia Defense Force Signal Operating Instructions:^[4]

Voice procedure is designed to provide the fastest and most accurate method of speech transmission. All messages should be pre-planned, brief and straightforward. Ideally, messages should be written down: even brief notes reduce the risk of error. Messages should be constructed clearly and logically in order not to confuse the recipient.

Voice procedure is necessary because:

1. Speech on a congested voice net must be clear, concise and unambiguous. To avoid interference between speech and data, it will often be expedient to assign the passage of data traffic to logistic or admin nets rather than to those directly associated with command and control.
2. It must be assumed that all transmissions will be intercepted by a portion of the civilian population. The use of a standard procedure will help reduce the threat of spreading rumors or creating panic among those not involved in an emergency response.
3. Some form of discipline is needed to ensure that transmissions do not overlap. If two people send traffic at the same time, the result is chaos.

Radio operators must talk differently because two-way radios reduce the quality of human speech in such a way that it becomes harder to understand. A large part of the radio-specific procedures is the specialized language that has been refined over more than 100 years.

There are several main methods of communication over radio, and they should be used in this order of preference:

1. Procedure words
2. Standard (predefined) phraseology (for most things in aviation and maritime use)
3. Plain language dialogue (for things that can't be handled by phraseology)
4. Formal messages
5. Narrative messages
6. Dialogue (normal conversation)
7. Brevity codes, including Ten-codes, and Phillips Code; and operating signals, including 92 code, Q code, and Z code; should be used as a last choice, as these lists of codes are so extensive that it is unlikely that all participants have the full and correct definitions memorized. All of those listed here except the ten-code are designed exclusively for use in Morse code or teletypewriter use, and are thus unsuitable for use on voice circuits.

International Radio Regulations

All radio communications on the planet operate under regulations created by the ITU-R, which prescribes most of the basic voice radio procedures, and these are further codified by each individual country.

United States radio regulations

In the U.S., radio communications are regulated by the NTIA and the FCC. Regulations created by the FCC are codified in Title 47 of the Code of Federal Regulations:

• Part 4—Disruptions to Communications
• Part 20—Commercial Mobile Services
• Part 80—Stations in the Maritime Services (Maritime Mobile Service)
• Part 87—Aviation Services
• Part 90—Private Land Mobile Radio Services (Concerning licensed wireless communications for businesses and non-federal governments)
  • Subpart C—Business Band
• Part 95—Personal Radio Services (MURS, FRS, GMRS, and CB radio)
• Part 97—Amateur Radio Service (Ham radio)
• Part 300—NTIA Rules and Regulations

Radio call signs

Radio call signs are a globally unique identifier assigned to all stations that are required to obtain a license in order to emit RF energy. The identifiers consist of from 3 to 9 letters and digits, and while the basic format of the call signs are specified by the ITU-R Radio Regulations, Article 19, Identification of stations,^[5] the details are left up to each country's radio licensing organizations.

Official call signs

Each country is assigned a range of prefixes, and the radiotelecommunications agencies within each country then responsible for allocating call signs, within the format defined by the RR, as they see fit. The Radio Regulations require most radio stations to regularly identify themselves by means of their official station call sign or other unique identifier.

Functional designators

Because official radio call signs have no inherent meaning outside of the above-described patterns, and other than individually licensed Amateur radio stations, do not serve to identify the person using the radio, they are not usually desirable as the primary means of identifying which person, department, or function is transmitting or is being contacted.

For this reason, functional designators (a.k.a. tactical call signs) are frequently used to provide such identification. Such designators are not sufficient to meet the FCC requirements that stations regularly identify the license they are operating under, typically every x number of minutes and at the end of each transmission, where x ranges from 10 to 30 minutes (longer for broadcast stations).

For the some radio services, the FCC authorizes alternate station IDs,^[6] typically in situations where the alternate station ID serves the purposes of identifying the transmitting station better than the standard ITU format. These include:

• Aircraft—the registration number (tail number) of the aircraft, preceded by the type (typical of general aviation aircraft); or the aircraft operator nickname assigned by the FAA, followed by the flight number (typical of scheduled airline services).
• Land mobile—Name of the station licensee (typically abbreviated), location of station, name of city, or facility served, followed by additional digits following the more general ID.
• Land mobile railroad—Name of railroad, followed by the train number, engine number etc.

Call signs in the United States

The United States has been assigned all call signs with the prefixes K, N, and W, as well as AAA–ALZ. Allocating call signs within these groups is the responsibility of the National Telecommunications and Information Administration (almost all government stations) or the Federal Communications Commission (all other stations), and they subdivide the radio call signs into the following groups:

Military call sign systems

• AAA–AEZ and ALA–ALZ are reserved for Department of the Army stations
• AFA–AKZ are assigned to the Department of the Air Force
• NAA–NZZ is jointly assigned to the Department of the Navy and the U.S. Coast Guard.

Amateur call sign systems

Ham station call signs begin with A, K, N or W, and have a single digit from 0 to 9 that separates the 1 or 2 letter prefix from the 1 to 3 letter suffix (special event stations have only three characters: the prefix, the digit, and a one-letter suffix).^[7]

Maritime call signs

Maritime call signs have a much more complex structure, and are sometimes replaced with the name of the vessel or a Maritime Mobile Service Identity (MMSI) number.

Microphone technique

Microphones are imperfect reproducers of the human voice, and will distort the human voice in ways that make it unintelligible unless a set of techniques are used to avoid the problems. The recommended techniques vary, but generally align with the following guidelines, which are extracted from the IARU Emergency Telecommunications Guide^[8]

• Hold the microphone close to your cheek, just off to the side of your mouth, positioned so that you talk across, and not into, the microphone. This reduces plosives (popping sounds from letters such as "P").
• Speak in a normal, clear, calm voice. Talking loudly or shouting does not increase the volume of your voice at the receiving radios, but will distort the audio, because loud sounds result in over-modulation, which directly causes distortion.
• Speak at a normal pace, or preferably, slower. Not leaving gaps between words causes problems with radio transmissions that are not as noticeable when one is talking face-to-face.
• Pronounce words carefully, making each syllable and sound clearly distinguishable.
• Adjust the microphone gain so that a normal voice 50 mm away from the microphone will produce full modulation. Setting the gain higher than that will transmit greater amounts of background noise, making your voice harder to hear, or even distorted. Noise-cancelling microphones can assist in this, but do not substitute for proper mic placement and gain settings.
• If you use a headset boom microphone, be aware that lower-cost models have omni-directional elements that will pick up background noise. Models with uni-directional or noise-cancelling elements are best.
• Do not use voice operated transmission (VOX) microphone circuits for emergency communication. The first syllable or so of each transmission will not actually be transmitted, while extraneous noises may also trigger transmission unintentionally.
• If not operating in a vehicle, use a foot push-to-talk switch so that both of your hands are free to transmit.
• Always leave a little extra time (1 second will suffice) between depressing the PTT switch and speaking. Numerous electronic circuits, including tone squelch, RF squelch and power-saving modes, need a substantial fraction of that time in order to allow your signal to be transmitted or received. This is especially true of repeaters, which might also have a "kerchunk" timer that prevents brief transmissions from keying the transmitter, and doubly true of linked repeaters, which have multiple sets of such circuits that must be activated before all stations can hear you.
• One must also leave gaps between the last station that transmitted and the next station, because such gaps are necessary to let other stations break in with emergency traffic. A pause of two seconds, approximated by a count of "one, one thousand" is sufficient in many conditions.

Similarly, the U.S. military radio procedures recommend headsets with noise-cancelling microphones:

Use of Audio Equipment. In many situations, particularly in noisy or difficult conditions, the use of headsets fitted with a noise cancelling microphone is preferable to loudspeakers as a headset will aid concentration and the audibility of the incoming signal. The double-sided, noise cancelling microphone is designed to cancel out surrounding noise, for example engine noise or gunfire, allowing speech entering on one side to pass freely. The microphone should be as close to the mouth as possible.^[9]

The U.S. Navy radio operator training manuals contain similar guidelines, including NAVPERS 10228-B, Radioman 3 & 2 training course (1957 edition):^[10]

Dos:

1. Do listen before transmitting. Unauthorized break-in is lubberly and causes confusion. Often neither transmission gets through.
2. Do speak clearly and distinctly. Slurred syllables and clipped speech are both hard to understand. A widespread error among untrained operators is failure to emphasize vowels sufficiently.
3. Do speak slowly. Unless the action officer is listening he will have to rely on the copy being typed or written at the other end. Give the recorder a chance to get it all the first time. You will save time and repetitions that way.
4. Do avoid extremes of pitch. A high voice cuts best through interference, but is shrill and unpleasant if too high. A lower pitch is easier on the ear, but is hard to understand through background noises if too low.
5. Do be natural. Maintain a normal speaking rhythm. Group words in a natural manner. Send your message phrase by phrase rather than word by word.
6. Do use standard pronunciation. Speech with sectional peculiarities is difficult for persons from other parts of the country. Talkers using the almost standard pronunciation of a broadcast network announcer are easiest to understand.
7. Do speak in a moderately strong voice. This will override unavoidable background noises and prevent drop-outs.
8. Do keep correct distance between lips and microphone. If the distance is too great, speech is inaudible and background noises creep in; if too small, blaring and blasting result.
9. Do shield your microphone. Turn your head away from noise generating sources while transmitting.
10. Do keep the volume of a hand set earphone low.
11. Do keep speaker volumes to a moderate level.
12. Do give an accurate evaluation in response to a request for a radio check. A transmission with feedback and/or a high level of background noise is not loud and clear even though the message can be understood.
13. Do pause momentarily, when possible, and interrupt your carrier. This allows any other station with higher precedence traffic to break in.
14. Do adhere strictly to prescribed procedures. Up-to-date radiotelephone procedure is found in the effective edition of ACP 125.
15. Do transact your business and get off the air. Preliminary calls only waste time when communication is good and the message short. It is NOT necessary to blow into a microphone to test it, nor to repeat portions of messages when no repetition has been requested.

Do Nots:

1. Don't transmit while surrounded by other persons loudly discussing the next maneuver or event. It confuses receiving stations, and a serious security violation can result.
2. Don't hold the microphone button in the push-to-talk position until absolutely ready to transmit. Your carrier will block communications on the net.
3. Don't hold a hand set in such a position while speaking that there is a possibility of having feedback from the earphone added to other extraneous noises.
4. Don't hold a hand set loosely. A firm pressure on the microphone button prevents unintentional release and consequent signal drop-out.
5. Don't send test signals for longer than 10 seconds.

Many radio systems also require the operator to wait a few seconds after depressing the PTT button before speaking, and so this is a recommended practice on all systems. The California Statewide EMS Operations and Communications Resource Manual explains why:

Key your transmitter before engaging in speech. The complexities in communications system design often introduce delay in the time it takes to turn on the various components comprising the system. Transmitters take time to come up to full power output, tone squelch decoding equipment requires time to open receivers and receiver voting systems take time to select the best receiver. While these events generally are accomplished in less than one second's time, there are many voice transmissions that could be missed in their entirety if the operator did not delay slightly before beginning his/her voice message. Pausing one second after depressing the push-to-talk button on the microphone or handset is sufficient in most cases to prevent missed words or responses.^[11]

Further, transmissions should be kept as short as possible; a maximum limit of 20 or 30 seconds is typically suggested:

Transmissions should generally be kept to less than 20 seconds, or within the time specifically allocated by the system. Most radio systems limit transmissions to less than 30 seconds to prevent malfunctioning transmitters or accidentally keyed microphones from dominating a system, and will automatically stop transmitting at the expiration of the allowed time cutting off additional audio.^[11]

Speech technique

Communicating by voice over two-way radios is more difficult than talking with other people face-to-face or over the telephone. The human voice is changed dramatically by two-way radio circuits. In addition to cutting off important audio bandwidth at both the low and high ends of the human speech spectrum (reducing the bandwidth by at least half), other distortions of the voice occur in the microphone, transmitter, receiver, and speaker—and the radio signal itself is subject to fading, interruptions, and other interference. All of these make human speech more difficult to recognize; in particular, momentary disruptions or distortions of the signal are likely to block the transmission of entire syllables.

The best way to overcome these problems is by greatly reducing the number of single-syllable words used. This is very much counter to the human nature of taking shortcuts, and so takes training, discipline, and having all operators using the same language, techniques, and procedures.^[12]

Method of speech

Several radio operation procedures manuals, including ACP 125(G) teach the same mnemonic of Rhythm, Speed, Volume, and Pitch (RSVP):^[13]

Rhythm

Use short sentences divided into sensible phrases which maintain a natural rhythm; they should not be spoken word by word. Where pauses occur, the press-to-talk should be released to minimize transmission time and permit stations to break in when necessary.

Speed

Speak slightly slower than for normal conversation. Where a message is to be written down by the recipients, or in difficult conditions, extra time should be allowed to compensate for the receiving station experiencing the worst conditions. Speed of transmission is easily adjusted by increasing or decreasing the length of pauses between phrases, as opposed to altering the gaps between words; the latter will create an unnatural, halted style of speech, which is difficult to understand.

Volume

Speak quietly when using whisper facilities, otherwise the volume should be as for normal conversation. Shouting causes distortion.

Pitch

The voice should be pitched slightly higher than for normal conversation to improve clarity.^[14]

According to the UK's Radiotelephony Manual, CAP 413, radio operators should talk at a speed of fewer than 100 words per minute.

Radio discipline

Communicating over a half-duplex, shared circuit with multiple parties requires a large amount of discipline in following the established procedures and conventions, because whenever one particular radio operator is transmitting, that operator can not hear any other station on the channel being used.^{[15][16][17][18]}

ABC—Accuracy, Brevity, Clarity

The initialism ABC is commonly used as a memory aid to reinforce the three most important rules about what to transmit.^[19]

The Five Ws

Whenever a report or a request is transmitted over a two-way radio, the operator should consider including the standard Five Ws in the transmission, so as to eliminate additional requests for information that may occur and thereby delay the request (and other communications).

1. Who—needs something
2. What—do they need
3. Why—do they need it
4. When—do they need it
5. Where—do they need it

Other rules

• Think before you speak^[20]
• Listen before you speak^[20]
• Answer all calls promptly^[20]
• Keep the airways free of unnecessary talk^[20]
• Be brief and to the point^[20]
• Only transmit facts^[21]
• Do not act as a relay station unless the net control asks for one^[21]

Voice procedures

The procedures described in this section can be viewed as the base of all voice radio communications procedures.

Service-specific procedures

However, the international aviation and maritime industries, because their global expansion in the 20th century coincided with, and were heavily integral to the development of voice procedures and other aspects in the development of two-way radio technology, gradually developed their own variations on these procedures.

Aeronautical Mobile Service

Voice communications procedures for international air traffic control and communications among airplanes are defined by the following International Civil Aviation Organization documents:

• Annex 10—Aeronautical Telecommunications, Volume II—Communications Procedures including those with PANS status,^[22][23]
• Procedures for Air Navigation Services—Air Traffic Management (PANS-ATM, ICAO Doc 4444)^[24]
• ICAO Doc 9432 (AN/925) Manual of Radiotelephony.^[25]

Refinements and localization of these procedures can be done by each member country of ICAO.

• United States
  • FAA Pilot Controller Glossary^[26]
• United Kingdom
  • Civil Aviation Authority's Radiotelephony manual^[27]

Maritime Mobile Service

Voice procedures for use on ships and boats are defined by the International Telecommunication Union and the International Maritime Organization bodies of the United Nations, and by international treaties such as the Safety of Life a Sea Convention (a.k.a. SOLAS 74), and by other documents, such as the International Code of Signals.

• ITU Radio Regulations
  • Appendix 18
• ITU maritime recommendations
  • ITU-R M.1171: Radiotelephony procedures in the maritime mobile service.^[28]
• IMO resolutions
  • Resolution A.918(22) (covers Standard Marine Communication Phrases)

Police procedures

In the U.S., the organization chartered with devising police communications procedures is APCO International, the Association of Police Communications Officers, which was founded in 1935. For the most part, APCO's procedures have been developed independently of the worldwide standard operating procedures, leading to most police departments using a different spelling alphabet, and the reverse order of calling procedure (e.g. 1-Adam-12 calling Dispatch).

However, APCO occasionally follows the international procedure standards, having adopted the U.S. Navy's Morse code procedure signs in the 1930s, and adopting the ICAO radiotelephony spelling alphabet in 1974, replacing its own Adam-Boy-Charles alphabet adopted in 1940, although very few U.S. police departments made the change.

APCO has also specified Standard Description Forms, a standard order of reporting information describing people and vehicles.

Standard description of persons

The Standard Description of Persons format first appeared in the April 1950 edition of the APCO Bulletin.^[29] It starts with a description of the person themself and finishes with a description of what they are wearing at the time.

Standard Description of Persons Form

Start	Finish
Name Color Sex Age Height Weight Hair Eyes Complexion Physical	Clothing Head to Foot Hat Shirt or Tie Coat Trousers Socks Shoes

Standard description of automobiles

APCO promotes the mnemonic CYMBALS for reporting vehicle descriptions:^[29]

APCO vehicle description format

Property	Example
Color	Red
Year	2001
Make	Ford
Body	F-150
Additional descriptive items	With a black camper shell
License	1234567
State	California

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