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.
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.
These procedures consist of many different components. The three most important ones are: Voice procedures—what to say Speech technique—how to say it 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. According to ACP 125(G) and the Virginia Defense Force Signal Operating Instructions: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: 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. 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. 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: Procedure words Standard (predefined) phraseology (for most things in aviation and maritime use) Plain language dialogue (for things that can't be handled by phraseology) Formal messages Narrative messages Dialogue (normal conversation) 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 licence 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, 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 licence 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, 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).
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 The user should: Hold the microphone close to the cheek, just off to the side of the mouth, positioned so that they 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 the 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 the user's 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 a headset boom microphone is involved, 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 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 a 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. 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.