🚀 go-pugleaf

Shuttle space-to-ground communications are primarily conducted
via S-band digital signals.  There are several channels around 2500 MHz,
with several different modes.  Voice is digitized and stuffed into 
the telemetry frames.  There are several different formats.  This is a
very hard signal to pick apart, to recover the voice.

There is an auxiliary UHF FM system for voice comm only.
It has three channels, and is designed to the parameters of a standard
UHF aircraft radio.  One channel is the UHF aircraft distress (GUARD)
frequency, 243.0 MHz.  This was included so that the Shuttle could talk
to the normal air traffic control system in emergencies.  The UHF voice
system is normally set to one of the other two channels, and fed audio
in parallel with the S-band.  Obviously, the UHF voice cannot be
encrypted, so it is turned off during secure flights.

I am reluctant to give the frequencies of the other two UHF channels,
because I don't know how many squirrels read this group.  I trust 95%
of you, but one bad apple could screw up a major national asset.  Sigh.
"Paranoia strikes deep" -- Buffalo Springfield.

A side note:  You may have wondered (I did) why there's not much
first-hand info about the Shuttle on the net.  Would you believe that
there is not a single Internet connection on site at Johnson Space
Center?  As far as I know, there are no USENET connections, either.
JSC is not as far out on the leading edge as you may have been led
to believe.  We are working on the problem, however.

Cheers!
Stewart Cobb, N5JXE
  << Insert the usual disclaimer >>