Along with the R-S-T systems radio operators use a set of codes called the Q-Codes. The origin of the Q codes date back to the early 1900s when they were used to simplify radio telegraph communication so that a three letter code could be sent instead of a much longer message. They have proved to be so useful that they are now widely used by all radio operators. They are especially useful where an operator is working a station (talking to another operator) that may have limited capacity to spend time on a longer conversation (QSO) or the other station may speak a different language and simple codes will make the the interaction a lot easier.

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For example: When an English-speaking operator receives QTH? they know that the other station is asking, “What is your location?” 

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A list of the current codes most widely used by radio operators are shown below: