Q code
The Q-code is a standardised collection of three-letter codes that each start with the letter "Q". It is an operating signal initially developed for commercial radiotelegraph communication and later adopted by other radio services, especially amateur radio. To distinguish the use of a Q-code transmitted as a question from the same Q-code transmitted as a statement, operators either prefixed it with the military network question marker "" (dit dit dah dit dah) or suffixed it with the standard Morse question mark (dit dit dah dah dit dit). 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; no country is ever issued an ITU prefix starting with "Q". Codes in the range QAA–QNZ are reserved for aeronautical use; QOA–QQZ for maritime use and QRA–QUZ for all services. "Q" has no official meaning, but it is sometimes assigned with a word with mnemonic value, such as "Queen's" (e.g. QFE: Queen's field elevation), "Query", "Question", or "reQuest". Early development. 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 Second 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: Later use. Over the years the original Q-codes were modified to reflect changes in radio practice. For example, QSW / QSX originally stood for, "Shall I increase / decrease my spark frequency?", but in the 1920s spark-gap transmitters were gradually being banned from land stations, making that meaning obsolete. By the 1970s, the "Post Office Handbook for Radio Operators" listed over a hundred Q-codes, covering a wide range of subjects including radio procedures, meteorology, radio direction finding, and search and rescue. 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 Organization. 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 Telecommunication 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 organisations 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 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", whereas an unprompted statement "QRP" means "Please 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. Aeronautical Code signals (QAA–QNZ; ICAO). First defined  in ICAO publication "Doc 6100-COM/504/1" and in "ICAO Procedures for Air Navigation Services, Abbreviations and Codes (PANS-ABC)" [Doc8400-4] (4th edition 1989), the majority of the Q-codes have fallen 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 computerised transmissions. But several remain part of the standard ICAO radiotelephony phraseology in aviation. These are also part of ACP131, which lists all ITU-R Q-codes, without grouping them by aeronautical/marine/general use. Maritime Mobile Service (QOA –QQZ). This assignment is specified in "RECOMMENDATION ITU-R M.1172". Q signals are not substantially used in the maritime service. Morse code is now very rarely used for maritime communications, but in isolated maritime regions like Antarctica and the South Pacific the use of Q-codes continues. Q-codes still work when HF voice circuits are not possible due to atmospherics and the nearest vessel is one ionospheric hop away. All services (QRA–QUZ). First defined by the Washington 1927 ITU Radio Regulations. Later defined by ITU-R in Appendix 9 to the Radio Regulations Annex to the "International Telecommunications  Convention" (Atlantic City, 1947). The current callsign table is found in ITU-R Appendix 42. Current interpretation of the Q-code can be found in ITU-R Appendices 14 and 15. ITU Radio Regulations 1990, Appendix 13: Miscellaneous Abbreviations and Signals to be Used in Radiotelegraphy Communications Except in the Maritime Mobile Service: Amateur radio. Amateur radio has adapted two different sets of Q-codes for use in amateur communications. The first set comes from the ITU civil series QRA through QUZ. Most of the meanings are identical to the ITU definitions, however, they must be looked at in the  context of amateur communications. For example, QSJ? asks what the charges are for sending the telegraph. Since amateur communications are without charge, this Q-code would not make sense. The second set is the set of QN Signals, used only in ARRL NTS nets. These operating signals generally have no equivalent in the ACP 131 publication or ITU publications, and are specifically defined only for use in ARRL NTS nets. They are not used in casual amateur radio communications. 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" (fading); "to QSY" is to change your operating frequency, or to break  in on a conversation QSK is often used even on VHF and UHF frequencies. (See also Informal usage, below.) Notes for response to radiotelegraph Q-codes. Responses to a radiotelegraph Q-code query or a Q-code assertion may vary depending upon the code. For Q-code assertions or queries which only need to be acknowledged as received, the usual practice is to respond with the letter "R" for "Roger" which means "Received correctly". Sending an "R" merely means the code has been correctly received and does not necessarily mean that the receiving operator has taken any other action. For  Q-code queries that need to be answered in the affirmative, the usual practice is to respond with the letter "C" (Sounds like the Spanish word "Si"). For Q-code queries that need to be answered in the negative, the usual practice it to respond with the letter "N" for "no". For those Q-code assertions that merely need to be acknowledged as understood, the usual practice is to respond with the prosign (or ) which means "understood". On telegraph cable networks "KK" was often used at the end of a reply to a Q-code to mean "OK" or "Acknowledged . This practice predates amateur radio as telegraph operators in the late 19th century are known to have used it. Informal usage. QLF – Are you sending with your left foot? Try sending with your left foot!" A humorously derogatory comment about the quality of a person's sending. QNB – QNB? “How many buttons on your radio?” “QNB 100/5” Means there are 100 and I know what 5 of them do. QSH – "Stay happy and healthy." QSK – "I can hear you during my transmission" – refers to a particular mode of Morse code operating often called QSK operation (full break-in) 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. QSY – "Change to transmission on another frequency"; colloquially, "move [=change address]". E.g., "When did GKB QSY from Northolt to Portishead?" QTH – "My location is ____"; colloquially in voice or writing, "location". E.g., "The OCF "[antenna type]" is an interesting build but at my QTH a disappointing performer." QTHR – "At  the registered location ____"; chiefly British use. Historically, the location in the printed Callbook; modernly, "as given in online government records for my callsign". E.g., "You can contact me QTHR". German use during World War II. During World War II, according to Bletchley Park’s "General Report on Tunny," German radio teleprinter networks used Q-codes to establish and maintain circuit connections. In particular: QKP [ought to be 'QEP', not 'QKP' - the print in the source document isn't very clear] was to indicate the Lorenz cipher machine setting for each message and, QZZ to indicate that the daily key change  was about to take place at the sender's station.