Morse code prosigns (AR, SK, BT, KN)

How to read it

ARRL’s glossary defines a procedural signal, or prosign, as one or two letters sent as a single character, written with a bar over the letters; ITU-R M.1172 says the bar means the letters “are to be sent as one signal”. ITU-R M.1677-1, the ITU’s definition of the code, lists most of them by what they do rather than by their letters: the cross signal, the double hyphen, end of work, invitation to transmit, wait and the eight-dot error signal. The names differ between the two: ARRL calls ···−·− SK, “end of QSO”, and ITU-R M.1172 lists the same signal as VA, end of work.

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The common prosigns

AR at the end of a message

The General class question pool that ARRL publishes for the US amateur exam gives AR as the prosign sent to indicate the end of a formal message. ITU-R M.1677-1 ends every telegram with the cross signal, and ends a transmission with the cross signal followed by K.

The error signal

ITU-R M.1677-1 gives the error signal as eight dots. ARRL lists the same eight dots, di-di-di-di-di-di-di-dit, and an alternate, di-dit dit-dit.

SK and “silent key”

ARRL’s glossary says “silent key”, SK, is amateurs’ term for an operator who has died. It traces the sound to the Western Union company’s “92 code”, where 30 meant “the end. No more.”: sent in landline Morse, 30 run together sounds the same as SK.

Look-alikes

A prosign shares its dots and dashes with a character, so one sound has two readings. In ITU-R M.1677-1, ·−·−· (AR) is also the plus sign, −···− (BT) the double hyphen or equals sign, and −·−−· (KN) the left-hand bracket. See Morse code punctuation. Abbreviations such as CQ are sent the other way, as separate letters.