Are the comms to the shuttle actually digital or analog?

Because they sure seem scratchy? Is this just added for effect? Why don't
they go digital? I am guessing because the voice coms are some sort of
seperate system that would be most robust FM on set frequency? It does seem
kind of stupid though, especially after listening to some digital russian
transmissions, the cosmonaught sounded clearer than the ground control.

Dac wrote:
Because they sure seem scratchy? Is this just added for effect? Why
don't they go digital? I am guessing because the voice coms are some
sort of seperate system that would be most robust FM on set
frequency? It does seem kind of stupid though, especially after
listening to some digital russian transmissions, the cosmonaught
sounded clearer than the ground control.

Lousy microphones and high levels of cabin noise are the likely
suspects. Shuttle communications have been all digital since the start.

See, for example,

IEEE Transactions on Communications - Special issue on Space Shuttle
Communications and Tracking, Vol. COM-26, No. 11, November l978

--
Dave Michelson

Dac wrote:
Because they sure seem scratchy? Is this just added for effect? Why don't
they go digital? I am guessing because the voice coms are some sort of

The voice comm system on the shuttle has always been digital. Voice
transmissions are encoded at 8kHz, 7 bits per sample in PCM mode, or
8kHz, 6 bits per sample in delta PCM mode, and are multiplexed along
with television and telemetry. This type of encoding gives you
approximately the same quality as the public telephone system in the US
(actually, a bit worse than that). When you combine the relatively low
frequency response of the encoding with the ambient noise in the crew
module, you basically get the 1960's-sounding comm that we've become
accustomed to.