[amsat-bb] Re: HF satellite?

Robert Bruninga bruninga at usna.edu
Fri Jun 5 12:55:25 PDT 2009

Some amplifying information on this HF transponder:

> ? long range = HEO / MEO or long range planning?


> Some rough and ready calculations *assuming 
> a LEO* are that PSK needs the TX frequency 
> adjusting every second or so...

Yes, the good news is that Doppler on the 2m downlink does not
impact the link, since it is FM.  But still even at 29 MHz, 90%
of the time the doppler rate is below 5 Hz/sec.  See our
original 2002 paper for PCSAT-2 and RAFT.

But this transponder has one big advantage, everyone's relative
position in the passband is seen the same by everyone at the
same time, and also, it is full duplex, so each stations uplink
software can compensate his own uplink so that he remains
exactly where he is.

10m/24m Transponder:  Actually, I forgot that we had talked
ourselves out of the HF/HF transponder since it would require
TWO HF rigs to be able to operate full duplex.  Instead we had
changed it to 2m SSB uplink and 10m downlink.  But then I guess
it could be either.
Come to think about it, so many rigs now have both VHF and HF, I
guess it makes sense to go that way.  But then the HF/HF
inverting transponder would have only 3% of the Doppler and
wouldn't that be a joy.  As you can see, we have not made up our

> Let's go for it. I'm keen on using the 
> unused "exclusive" HF satellite 
> allocations. I hope many of us will be 
> interested in supporting the concept.
> Bill - N6GHz

In order to get funding, we are proposing it as a "satcom"
system for vehicles, boats and planes that only have old HF and
UHF(AM) transceivers.  Those low value platforms will never get
satcom, but we can build a cubesat to provide it.  Of course, it
is just a demo with the UHF up and HF down, but all the rest of
the time, we will have the links in the Amateur Satelltie
Service bands for us.  The UHF AM uplink would not be used for
amateur radio, but the HF downlink would be available for the
amateur transponders we mentioned above.


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