A prosign, short for procedural sign, is a Morse signal made by running two or more letters together without the usual gap between them, so they sound like one character. Prosigns are not words; they are instructions about the conversation itself, such as "end of message", "wait" or "I made a mistake". The best known is SOS.
How a prosign differs from letters
Between two letters, Morse leaves a gap of three units. In a prosign that gap disappears. Compare the two letters A and R, .- .-., with the prosign AR, .-.-.. The dots and dashes are the same; only the rhythm changes. To a trained ear, the prosign is a single, unmistakable shape.
Because a prosign is one character, it is written with a line over the letters, or in angle brackets: <AR> in angle brackets sends it as one prosign.
The prosigns you will hear most
| Prosign | Code | Meaning |
|---|---|---|
| AR | .-.-. |
End of message |
| SK | ...-.- |
End of contact; the line is now free |
| K | -.- |
Over: go ahead, anyone may answer |
| KN | -.--. |
Go ahead, but only the station I am talking to |
| BT | -...- |
Break: start of a new section |
| AS | .-... |
Wait, I must pause |
| HH | ........ |
Correction: the last word was wrong |
| CT | -.-.- |
Starting signal: a message follows |
| SOS | ...---... |
Distress: the start of a distress message |
Tap any code in the table to hear it.
What each one is for
AR, end of message. Sent at the end of a message, before handing over. It has the same code as the plus sign, .-.-., which is why decoders sometimes print a + where an operator meant AR.
SK, end of contact. The last thing sent in a conversation: we are finished, the frequency is free. The last commercial Morse transmission in the United States, on 12 July 1999, signed off with "What hath God wrought" and SK.
K and KN, over. K on its own, -.-, means "go ahead": anyone listening may reply. KN, -.--., means "go ahead, but only you": it keeps other stations from jumping into a conversation. KN shares its code with the opening bracket.
BT, break. Separates parts of a message, like a new paragraph. It is the same code as the equals sign, -...-, and you will often see it printed as =.
AS, wait. .-... asks the other station to stand by for a moment.
HH, correction. Eight dots, ......... It means the word just sent was wrong; the sender then repeats it correctly. Eight dots is easy to recognise and impossible to confuse with any letter, which is the point.
CT, starting signal. -.-.- marks the start of a formal message.
SOS, distress. ...---..., sent as one run with no gaps. Its meaning is closer to "this is a distress message, everyone else stay silent" than to any word. The full story is in what does SOS stand for.
Prosigns in a real exchange
A short contact between two radio amateurs might end like this:
TU FER QSO 73 SK
That is "thank you for the contact, best regards, end of contact". TU, FER and 73 are abbreviations; QSO is a Q code; SK is the prosign. The abbreviations and Q codes have their own guide.
Prosigns and punctuation
Several prosigns share their codes with punctuation marks, because both were defined from the same limited set of dot-and-dash patterns: AR is +, BT is =, KN is the opening bracket. Context tells an operator which is meant. A decoder program cannot know, so it prints one or the other, and you may see "73 +" at the end of a transcript where the operator sent "73 AR".
Learning them
Prosigns are learned by sound, as a single rhythm, just like letters. Once you know the alphabet, they come quickly, and they make on-air Morse much easier to follow. The alphabet chart has a section of prosigns you can tap to hear, and how to learn Morse code covers the method.