Morse code prosigns explained: AR, SK, BT, KN and more
A Morse code prosign is two or more letters sent as a single character, with no letter gap between them. AR, sent as one continuous rhythm .-.-., means end of message. SK, ...-.-, means end of contact. BT, -...-, is a break or a new paragraph, and KN, -.--., means go ahead, but only the station I am working. On paper, prosigns are written with a bar over the letters or in angle brackets, like <AR>, so that nobody reads them as two separate letters.
One character, not two letters
The difference between a prosign and the letters it is named after is a single gap.
Send A, .-, then a three-unit letter gap, then R, .-., and the receiver writes down two letters: .- .-.. Close that gap to the one unit that belongs inside a character and the same five elements become one character, .-.-., di-dah-di-dah-dit. That is AR.
So the letters are only a name for the pattern, a way to say it and write it. That is also why some prosigns have two names. The understood signal ...-. can be split as S and N or as V and E, so it is written SN or VE. The starting signal -.-.- splits as C and T or as K and A, so it is CT or KA. Either name describes the same sound.
When you write a prosign down, use one of the two marks that show it is joined:
- A bar over the letters. The traditional written form, easy with a pencil and awkward on a keyboard.
- Angle brackets.
<AR>,<SK>,<BT>. This is the usual form in typed text.
Some people simply write the letters together, AR, and trust the context. That works in a conversation about Morse, but on a message form it invites someone to send the two letters with a gap.
The common prosigns
| Prosign | Code | Rhythm | Meaning |
|---|---|---|---|
| AR | .-.-. |
di-dah-di-dah-dit | End of message |
| SK | ...-.- |
di-di-di-dah-di-dah | End of contact, end of work |
| BT | -...- |
dah-di-di-di-dah | Break, new paragraph |
| KN | -.--. |
dah-di-dah-dah-dit | Go ahead, only the station I am working |
| AS | .-... |
di-dah-di-di-dit | Wait |
| HH | ........ |
di-di-di-di-di-di-di-dit | Error |
| SN or VE | ...-. |
di-di-di-dah-dit | Understood |
| CT or KA | -.-.- |
dah-di-dah-di-dah | Starting signal |
| SOS | ...---... |
di-di-di-dah-dah-dah-di-di-dit | Distress |
Alongside these sits K, -.-, dah-di-dah, which means “over”: an invitation to transmit. K is an ordinary letter, so there is nothing special about how you send it, but it does the same procedural job as the prosigns.
The error signal deserves a word of its own. The ITU’s error signal is eight dits, ........, which is HH run together. Send all eight. At speed they are hard to count, but a run cut short to four or five dits reads as H or the figure 5. After it, send the word again, correctly this time. The Morse code error signal goes into what comes next in more detail.
Prosigns that share a code with punctuation
Four of the common prosigns use exactly the same pattern as a punctuation mark:
| Prosign | Code | Same code as |
|---|---|---|
| AR | .-.-. |
Plus sign + |
| BT | -...- |
Equals sign = |
| KN | -.--. |
Open parenthesis ( |
| AS | .-... |
Ampersand & |
There is only one sound, so the receiver decides from context. -...- between two sentences of a chat is a break; in the middle of a sum it is an equals sign. .-.-. at the end of a transmission is AR; between two figures it is a plus. On the air the procedural meaning is the usual one; in written text, the punctuation. Morse code punctuation lists the full set of marks.
How prosigns work in a contact
In an amateur radio contact in Morse, prosigns and a few letters steer the conversation, so both sides know whose turn it is and when it is over. Here is the outline, using K1ABC and K2ABC, both made-up callsigns:
- K1ABC calls. It sends CQ (calling any station), DE (from) and its callsign, and ends with K: anyone may answer.
- K2ABC answers with both callsigns.
- They talk in turns. A turn often ends with KN, which tells any third station listening not to break in: only the station being worked should reply. BT separates topics within a turn, the way a new paragraph would.
- A message ends with AR.
- The last turn ends with SK. It closes the contact, often after 73, best regards.
Operators vary in the details, and you will hear plenty of contacts that do not follow this shape exactly. How a basic CW contact works walks through a full exchange.
SOS, the best-known prosign
SOS is a prosign too: one character of nine elements, ...---..., sent with only the one-unit gaps that belong inside a character. Sent with letter gaps, ... --- ..., it is just the letters S, O and S.
The letters do not stand for anything. “Save Our Souls” and similar readings came later; what makes SOS useful is the pattern itself, three dits, three dahs, three dits, easy to send and hard to mistake. SOS was adopted at the International Radiotelegraph Convention in Berlin in 1906 and came into force in 1908. Before it, the Marconi company’s operators used CQD as their distress call. SOS in Morse code covers how to send it.
SOS on the air is for real distress only. In an emergency today, call your local emergency number.
How to send prosigns cleanly
Learn each one as its own sound. Think di-dah-di-dah-dit, not “A, R”. If you learn AR as two letters, you will tend to leave a gap at the join, and the receiver will write down A R.
Check the join. A common prosign fault is a slight pause in the middle. If something reads your Morse back to you and prints two letters where you meant one character, a letter gap crept in. Recording yourself and listening later works too.
Send the error signal evenly. Eight even dits, a pause, then the word again. A ragged string of dits only costs time.
Keep the sound distinct from its punctuation twin. In a practice text full of plus signs or equals signs, you will start to hear AR and BT as punctuation. That is fine. The pattern is the same; only the meaning changes.
If you practice on a Mac, the last two chapters of the course in Dot & Dash teach the common prosigns: AR and BT in chapter 19, then SK and the error signal (HH) in chapter 20. Its Text to Morse reads <AR>, <BT>, <SK> and <HH> in angle brackets as prosigns, and when you key into other apps with its Type Anywhere, the error signal deletes the last word it typed, while AR, BT and SK type nothing.
Questions
Is SOS a prosign?
Yes. SOS is sent as one continuous character, ...---..., with no letter gaps between the S, the O and the S. Sent with letter gaps, it is just the letters S, O and S, not the prosign.
What is the difference between K and KN?
Both mean “over”. K is an invitation to transmit, while KN means go ahead, but only the station I am working, so others should not break in.
Why does AR sound the same as the plus sign?
They share one pattern, .-.-.. At the end of a transmission it is read as AR, end of message; in written text or between figures it is read as a plus sign.
How do I write a prosign in plain text?
Put its letters in angle brackets, such as <SK>, or draw a bar over them by hand. Either form tells the sender to run the letters together as one character.