[amsat-bb] DIGITAL modes

[Bob Bruninga <bruninga@xxxxxxxxxxxxx>]

Concerning the advantages of DIGITAL:

I'm hoping for the day we do Satellite HAM ATV.  It just wont happen
with 6 MHz wide bandwidth analog.

At a local ATV demo, a local ham demonstrated 300 KB ATV digital
video. It was crystal clear and had noticible choppy video (kind of like
what you see in teleconferencing etc.  But 100% adequate for all of the
ATV applications I have ever seen...

But the neat thing was that he showed the spectrum on a spectrym analyzer.
It took less than 1 MHz, thus a more than 7 dB advantage in bandwidth.
But then add the fact that you need a 30 dB S/N ratio for a good picture..
Ok lets say 20 dB for a usable picture...

whereas with a 10 dB S/N digital signal you can still decode a "perfect"
picture, the overall improvement is more like 17 dB!  SO instead of
needing a KW and an EME antenna to do Satellite ATV, you will be able to
do it with only 50 watts and a decent antenna.

HISTORY NOTE:  When we were one of the first stations to ever UPLINK Live
ATV to the Space SHuttle on mission STS-37, we were using a 300W amp and a
40 FOOT dish antenna.  With digital, we could have done it with an ARROW
antenna.

But I AGREE 100%, that all amateur use of digital MUST use 1-to-ALL
protocols so we can all "read the mail"...

de WB4APR, Bob


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