In article k.net, "Brian"
writes:

We sign with SK at the end of a CW QSO. Not VA.



SK: ... _._

VA: ..._ ._

They sound very similar.

Actually, the letters in prosigns are run together:

....-.-

didididahdidah

That's why you see the SK or VA written with a bar overline in books on the
subject.

It's actually a contracted version of the American Morse "30" meaning "end of
work, no more to follow".

73 is used because of the way it sounds....

dah dah di di dit di di dit dah dah


Except it doesn't sound that way in American Morse, where its use originated.
That rhythm is one reason it stayed popular among radio operators but the true
origin is the old land wire number code lists.

73 de Jim, N2EY