Tony Meloche wrote:

I had no sooner sent that post than I remembered a similar experience
in my own listening.

One summer day, 20 years ago, I got quite clearly on the cheap SW I
was using at that time, a transmission between two men. The "first" man
spoke with a soft Texas drawl, and the "second" man sounded like an
urban African-American. The first man slowly and clearly spoke a series
of numbers, then the second man repeated them equally clearly. First
man again spoke a series of numbers, finishing with the word "End". The
second man repeated them, finishing with the words "End. Got it!" The
first man replied "OK, buddy!" and the transmission ended right there
(return to background hiss). I asked a shortwave maven at the time what
he thought it was, and he offhandedly replied: "That's the Army".

And again - for what it's worth.

Maybe it's a military broadcast from South of the Border. The US
military today uses vastly more complex encryption than was possible in
1983, but it's possible that a less advanced army-maybe Mexico or
Colombia-is still using outdated encoding.