The Q code is a standardized collection of three-letter message encodings, also known as a brevity code, all of which start with the letter "Q", initially developed for commercial radiotelegraph communication, and later adopted by other radio services, especially amateur radio. Although Q codes were created when radio used Morse code exclusively, they continued to be employed after the introduction of voice transmissions. To avoid confusion, transmitter call signs are restricted; while an embedded three-letter Q sequence may occur (for instance when requested by an amateur radio station dedicated to low-power operation), no country is ever issued an ITU prefix starting with "Q". The codes in the range QAA–QNZ are reserved for aeronautical use; QOA–QQZ for maritime use and QRA–QUZ for all services.
Early developments 
The original Q codes were created, circa 1909, by the British government as a "list of abbreviations... prepared for the use of British ships and coast stations licensed by the Postmaster General". The Q codes facilitated communication between maritime radio operators speaking different languages, so they were soon adopted internationally. A total of forty-five Q codes appeared in the "List of Abbreviations to be used in Radio Communications", which was included in the Service Regulations affixed to the Third International Radiotelegraph Convention in London (The Convention was signed on July 5, 1912, and became effective July 1, 1913.)
The following table reviews a sample of the all-services Q codes adopted by the 1912 Convention:
First Twelve Q Codes Listed in the 1912 International Radiotelegraph Convention Regulations
|Code||Question||Answer or Notice|
|QRA||What ship or coast station is that?||This is ____.|
|QRB||What is your distance?||My distance is ____.|
|QRC||What is your true bearing?||My true bearing is ____ degrees.|
|QRD||Where are you bound for?||I am bound for ____.|
|QRF||Where are you bound from?||I am bound from ____.|
|QRG||What line do you belong to?||I belong to the ____ Line.|
|QRH||What is your wavelength in meters?||My wavelength is ____ meters.|
|QRJ||How many words have you to send?||I have ____ words to send.|
|QRK||How do you receive me?||I am receiving (1-5) where 1 is unreadable and 5 is perfect.|
|QRL||Are you busy?||I am busy.|
|QRM||Are you being interfered with?||I am being interfered with.|
|QRN||Are the atmospherics strong?||Atmospherics are very strong.|
Later usage 
Over the years, modifications were made to the original Q codes to reflect changes in radio practice. In the original international list, QSW/QSX stood for "Shall I increase/decrease my spark frequency?", however, spark-gap transmitters were banned in the United States in the 1920s, rendering the original meaning of those Q codes obsolete. Over a hundred Q codes were listed in the Post Office Handbook for Radio Operators in the 1970s and cover subjects such as meteorology, radio direction finding, radio procedures, search and rescue, and so on.
Some Q codes are also used in aviation, in particular QNE, QNH and QFE, referring to certain altimeter settings. These codes are used in radiotelephone conversations with air traffic control as unambiguous shorthand, where safety and efficiency are of vital importance. A subset of Q codes is used by the Miami-Dade County, Florida local government for law enforcement and fire rescue communications, one of the few instances where Q codes are used in ground voice communication.
The QAA–QNZ code range includes phrases applicable primarily to the aeronautical service, as defined by the International Civil Aviation Organisation. The QOA–QQZ code range is reserved for the maritime service. The QRA–QUZ code range includes phrases applicable to all services and is allocated to the International Telecommunications Union. QVA–QZZ are not allocated. Many codes have no immediate applicability outside one individual service, such as maritime operation (many QO or QU series codes) or radioteletype operation (the QJ series).
Many military and other organizations that use Morse code have adopted additional codes, including the Z code used by most European and NATO countries. The Z code adds commands and questions adapted for military radio transmissions, for example, "ZBW 2", which means "change to backup frequency number 2", and "ZNB abc", which means "my checksum is abc, what is yours?"
Used in their formal "question/answer" sense, the meaning of a Q code varies depending on whether or not the individual Q code is sent as a question or an answer. For example, the message "QRP?" means "Shall I decrease transmitter power?", and a reply of "QRP" means "Yes, decrease your transmitter power". This structured use of Q codes is fairly rare and now mainly limited to amateur radio and military morse code (CW) traffic networks.
Breakdown by service 
- QAA to QNZ - Assigned by the International Civil Aviation Organization (ICAO).
- QOA to QQZ - For the Maritime Services.
- QRA to QUZ - Assigned by the International Telecommunications Union (ITU).
Amateur radio 
Selected Q codes were soon adopted by amateur radio operators. In December, 1915, the American Radio Relay League began publication of a magazine titled QST, named after the Q code for "General call to all stations". In amateur radio, the Q codes were originally used in Morse code transmissions to shorten lengthy phrases and were followed by a Morse code question mark (··--··) if the phrase was a question.
Q codes are commonly used in voice communications as shorthand nouns, verbs, and adjectives making up phrases. For example, an amateur radio operator will complain about QRM (man-made interference), or tell another operator that there is "QSB on the signal"; "to QSY" is to change your operating frequency.
Q codes applicable for use in amateur radio 
|Code||Question||Answer or Statement|
|QRA||What is the name (or call sign) of your station?||The name (or call sign) of my station is ...|
|QRG||Will you tell me my exact frequency (or that of ...)?||Your exact frequency (or that of ... ) is ... kHz (or MHz).|
|QRH||Does my frequency vary?||Your frequency varies.|
|QRI||How is the tone of my transmission?||The tone of your transmission is (1. Good; 2. Variable; 3. Bad)|
|QRJ||How many voice contacts do you want to make?||I want to make ... voice contacts.|
|QRK||What is the readability of my signals (or those of ...)?||The readability of your signals (or those of ...) is ... (1 to 5).|
|QRL||Are you busy?||I am busy. (or I am busy with ... ) Please do not interfere.|
|QRM||Do you have interference?||I have interference.|
|QRN||Are you troubled by static?||I am troubled by static.|
|QRO||Shall I increase power?||Increase power.|
|QRP||Shall I decrease power?||Decrease power.|
|QRQ||Shall I send faster?||Send faster (... wpm)|
|QRS||Shall I send more slowly?||Send more slowly (... wpm)|
|QRT||Shall I cease or suspend operation?/ shutoff the radio||I am suspending operation. /shutting off the radio|
|QRU||Have you anything for me?||I have nothing for you.|
|QRV||Are you ready?||I am ready.|
|QRW||Shall I inform ... that you are calling him on ... kHz (or MHz)?||Please inform ... that I am calling him on ... kHz (or MHz).|
|QRX||When will you call me again?||I will call you again at ... (hours) on ... kHz (or MHz)|
|QRZ||Who is calling me?||You are being called by ... on ... kHz (or MHz)|
|QSA||What is the strength of my signals (or those of ... )?||The strength of your signals (or those of ...) is ... (1 to 5).|
|QSB||Are my signals fading?||Your signals are fading.|
|QSD||Is my keying defective?||Your keying is defective.|
|QSG||Shall I send ... telegrams (messages) at a time?||Send ... telegrams (messages) at a time.|
|QSK||Can you hear me between your signals?||I can hear you between my signals.|
|QSL||Can you acknowledge receipt?||I am acknowledging receipt.|
|QSM||Shall I repeat the last telegram (message) which I sent you, or some previous telegram (message)?||Repeat the last telegram (message) which you sent me (or telegram(s) (message(s)) numbers(s) ...).|
|QSN||Did you hear me (or ... (call sign)) on .. kHz (or MHz)?||I did hear you (or ... (call sign)) on ... kHz (or MHz).|
|QSO||Can you communicate with ... direct or by relay?||I can communicate with ... direct (or by relay through ...).|
|QSP||Will you relay a message to ...?||I will relay a message to ... .|
|QSR||Do you want me to repeat my call?||Please repeat your call; I did not hear you.|
|QSS||What working frequency will you use?||I will use the working frequency ... kHz (or MHz).|
|QST||-||Here is a broadcast message to all amateurs.|
|QSU||Shall I send or reply on this frequency (or on ... kHz (or MHz))?||Send or reply on this frequency (or on ... kHz (or MHz)).|
|QSW||Will you send on this frequency (or on ... kHz (or MHz))?||I am going to send on this frequency (or on ... kHz (or MHz)).|
|QSX||Will you listen to ... (call sign(s) on ... kHz (or MHz))?||I am listening to ... (call sign(s) on ... kHz (or MHz))|
|QSY||Shall I change to transmission on another frequency?||Change to transmission on another frequency (or on ... kHz (or MHz)).|
|QSZ||Shall I send each word or group more than once?||Send each word or group twice (or ... times).|
|QTA||Shall I cancel telegram (message) No. ... as if it had not been sent?||Cancel telegram (message) No. ... as if it had not been sent.|
|QTC||How many telegrams (messages) have you to send?||I have ... telegrams (messages) for you (or for ...).|
|QTH||What is your position in latitude and longitude (or according to any other indication)?||My position is ... latitude...longitude|
|QTR||What is the correct time?||The correct time is ... hours|
|QTU||At what times are you operating?||I am operating from ... to ... hours.|
|QTX||Will you keep your station open for further communication with me until further notice (or until ... hours)?||I will keep my station open for further communication with you until further notice (or until ... hours).|
|QUA||Have you news of ... (call sign)?||Here is news of ... (call sign).|
|QUC||What is the number (or other indication) of the last message you received from me (or from ... (call sign))?||The number (or other indication) of the last message I received from you (or from ... (call sign)) is ...|
|QUD||Have you received the urgency signal sent by ... (call sign of mobile station)?||I have received the urgency signal sent by ... (call sign of mobile station) at ... hours.|
|QUE||Can you speak in ... (language), - with interpreter if necessary; if so, on what frequencies?||I can speak in ... (language) on ... kHz (or MHz).|
|QUF||Have you received the distress signal sent by ... (call sign of mobile station)?||I have received the distress signal sent by ... (call sign of mobile station) at ... hours.|
Some of the common usages vary somewhat from their formal, official sense. QRL? is the accepted form of the question, "Is this frequency in use (or busy)?", the reply to which is typically the letters "C" (dah di dah dit), "R" (di dah dit) or "Y" (dah di dah dah) which, in the Amateur radio tradition, are the Morse code shorthand for "Confirm", "Roger" or "Yes." There are also a few unofficial and humorous codes in use, such as QLF ("try sending with your LEFT foot") and QSC ("send cigarettes", not the official meaning of "this is a cargo vessel"). In the question form, QNB?, is supposed to mean "How many buttons does your radio have?" A reply of the form QNB 45/15 means "45, and I know what 15 of them do." QSJ is sometimes used to refer to the cost of something - "I would like an FT9000 but it is too much QSJ". (QSJ actually means "What is the charge to be collected to ... including your internal charge?").
QSK - "I can hear you during my transmission" - refers to a particular mode of Morse code operating in which the receiver is quickly enabled during the spaces between the dits and dahs, which allows another operator to interrupt transmissions. Many modern transceivers incorporate this function, sometimes referred to as full break-in as against semi-break-in in which there is a short delay before the transceiver goes to receive.
A conversation or contact via amateur radio is often referred to as a QSO, while QSL cards are collected by both radioamateurs and shortwave listeners as confirmation of having received the signal of a particular station.
Regarding the speed of the Morse code being sent, if the speed is too fast and the receiving operator cannot copy the code at said speed, that operator may send "QRS", the request to "please slow down." A courteous sender will slow down to match the speed of the slower operator.
QTHR - "at the registered address for my callsign", this is used mainly in the United Kingdom and former colonies. Since business may not be discussed on amateur radio, a ham who has personal equipment to sell might say something like "I have a spare Morse key old chap, please contact me QTHR".
Note: The ARRL codes QNA-QNZ overlap with International Civil Aviation Organization (ICAO) codes but have different meanings.
The majority of the Q codes have slipped out of common use; for example today reports such as QAU ("I am about to jettison fuel") and QAZ ("I am flying in a storm") would be voice or computerized transmissions. But several remain part of the standard ICAO radiotelephony phraseology in aviation.
|QFE||Atmospheric pressure at sea level, corrected for temperature and adjusted to a specified datum such as airfield elevation. When set on the altimeter it reads height.||Runway in use 22 Left, QFE 990 millibars|
|QFF||Barometric pressure at a place, reduced to MSL using the actual temperature at the time of observation as the mean temperature.|
|QNE||Atmospheric pressure at sea level in the International Standard Atmosphere (ISA), equal to 1013.25 mbar or hPa and used as reference for measuring the pressure altitude. When Flight Levels are used as an indication of altitude, 1013.25hPa is used as mean sea level (QNH).|
|QNH||Atmospheric pressure at mean sea level (may be either a local, measured pressure or a regional forecast pressure (RPS)). When set on the altimeter it reads altitude.||Request Leeds QNH|
|QDM||Magnetic heading to a station||(callsign) request QDM (callsign) |
|QDL||Series of bearings taken at regular intervals|
|QDR||Magnetic bearing from a station||(callsign) request QDR (callsign) |
|QFU||Magnetic bearing of the runway in use||Runway 22 in use, QFU 220|
|QGH||Controlled Descent through Clouds (Royal Air Force use)|
|QTE||True bearing from a station||True bearing, True bearing, (callsign) request QTE (callsign) |
|QTF||Position in relation to a point of reference or in latitude and longitude|
|QUJ||True bearing to a station|
|QGH||controller-interpreted DF let-down procedure, on UHF or VHF|
Q signals are no longer used in the maritime service, as Morse code is now very rarely used.
See also 
- Prosigns for Morse code
- International Code of Signals
- International maritime signal flags
- National Communications Magazine. Radio codes & signals - Florida. Retrieved 2010-01-30.
- The Q Code
- ICAO PANS (Procedures for Air Navigation Services) Doc 8400: The ICAO Q Code.
- www.portland-amateur-radio-club.org.uk - Web site hosted by Freeola.com
- ACP 131(E), Communications Instructions - Operating Signals, March 1997. Chapter 2 contains a full list of 'Q' codes
- "International Morse code Recommendation ITU-R M.1677-1". itu.int. International Telecommunication Union. October 2009. Retrieved 23 December 2011.
- QFU on The Free Dictionary
- QGH on The Free Dictionary
- Handbook for Wireless Telegraph Operators, October, 1909.
- Radio Laws and Regulations of the United States: Edition July 27, 1914. (Includes the 1912 London Radiotelegraphic Convention)
- List of Q codes
- A resource for Morse Code operation in the amateur radio hobby