The Q code is a set of three-letter code signals to be used in radiotelegraphy and amateur radio communications. It was developed and instituted in 1912 as a way to facilitate communication between maritime radio operators of different nationalities. For this reason, callsigns never begin with a Q.

Used in their formal "question/answer" sense, their meaning varies depending on whether they are 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 United States amateur radio CW traffic networks.

In modern everyday amateur radio practice, the Q codes are more commonly used as shorthand nouns, verbs, or adjectives. For example, one will sometimes hear a ham complaining about QRM or telling another ham that he "has QSB on his signal"; if a ham wants you to change your operating frequency, she will ask you to QSY. Although the Q codes were created for use during Morse code operation, they are now commonly used in voice modes too. The following table gives the most common Q codes used in the amateur service, along with their meaning and sample use.

CodeMeaningSample use
Q Codes used commonly used in amateur practice
QRLIs this frequency busyUsed almost exclusively with Morse code
QRMMan-made interferenceThere's another QSO up 2 kHz that's causing you a lot of QRM
QRNStatic crashesThe band is noisy today; I'm hearing a lot of QRN
QRPLow transmitting powerI'm using a QRP transmitter here, running only 3 watts
QRSSend your Morse code more slowlyPlease QRS, I'm new to Morse code
QRTStop sendingI've enjoyed talking to you, but I have to QRT for dinner now
QRVActive; in useWill you be QRV in the upcoming contest?
QRXHang on a minute, I'll be right backPlease QRX one
QRZWho is calling me?QR Zed? I hear someone calling, but you're very weak
QSBFading of signalI'm hearing a lot of QSB on your signal
QSLAcknowledge receiptI QSL your last transmission
QSOA conversation with another hamThanks very much for the QSO
QSYChange frequencyLet's QSY up 5 kiloHertz
QTHLocationMy QTH is South Park, Colorado
QTRExact timeQTR is 2000 Z

Some of these common usages vary somewhat from their formal, official sense.

Some Q codes are also used in aviation, in particular QNH and QFE, referring to certain air pressures. These codes are used in radio conversations with air traffic control as unambiguous shorthand, where safety and efficiency are of vital importance.

See also: Common Morse code abbreviations in the Morse code article

External links