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SSB v FM birds...my $0.02 worth



G'day all,

Been sort of following this thread for a few days and thought I'd wade in a
little.

I've been following, tho not actively , the AMSAT program since Australis
OSCAR 5. 

The original thinking behind CW/SSB operation was purely a power
budget/bandwidth consideration. Batteries and solar cells were extremely
expensive (still are!!) as was the weight involved getting them into orbit.
FM (voice) has a duty cycle of 100%, SSB aroun 50% without speech
processing and CW considerably less, depending on the operator. It quite
simply takes less power for the same ability to communicate. Since all
users share the same power/bandwidth it made for more users/kHz too.

The "old" linear transponders would support FM... I know, I tried it and
got severely "corrected". After all, they simply took the uplink, mixed and
amplified it and sent it down again! Don't know about the newer sats as
they have DSP functions etc and are generally far more complicated.

To put a little perspective on things, we are facing a battle to keep our
70cm band here. The Police and varous "Public Safety" organisations wan't
it. (We are secondary users to the military.) We've already had to
relinquish some for the Olympics. A couple of REALLY easy sats with FM up
at one of the 70cm band and down at the other would sure help populate the
band!



Norm, VK2XCI.
Mount Hope NSW. Voice of the Edge of The Outback
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