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Re: [psk31] PSK31 satellite ideas

On Tue, 27 Feb 2001, Peter Martinez G3PLX wrote:
> My own idea for a PSK31 satellite .. would have a 3 kHz wide linear
> uplink on a low band like 29MHz and an FM downlink, probably on VHF...
> 1) satellite transmitter doesn't have to be linear...
> 2) There is no downlink Doppler on the demodulated baseband audio...
> 3) the level of audio I receive from my own return signal is precisely
>    related to my uplink signal level received at the satellite.
> 4) it will be possible for users to monitor their own signal coming
>    back and  tweek their uplink to [stay on channel and power]
> 5) [since this design] cancels out ALL the frequency errors, [users can 
>    meet or plan on certain specific AUDIO frequencys and "be there"...]
> The SSB-to-FM scheme would be much easier for amateurs at all skill
> levels to use effectively, especially for downlink-only listeners.

Great idea Peter!  I think it is perfect in accomplishing about everything
I'd like to see in a tiny cubesat design.  The only problem in stuffing
this in the 4" cubesat is the power budget required to keep an FM
transmitter on full time.  So here are some ways to fine tune the design:

1) Need a COR circuit to let the transmitter rest (charge) over the 90% of
the earth without HAMS in range...  

2) I think we still want a dedicated "tune up" subband to permit the
ground software to XMT until it finds itself in the passband.  Of course a
pass always starts with having to send - 600 Hz, so there is no reason why
the first guess cannot be within a 200 Hz or so.  THis way, the initial
"find-my-doppler" process does not interfer with QSO's that may be in
progress.  (We do not want to encubmer the PSK-31 users software with
having to do orbit math to predict doppler)  It should just start at -500
Hz and look for its own QRXQRZQRZQRZ stream in this "tune-up" subband.
(each station would genereate its own random XYXYXYXYX stream for tuneup)

Hows this for a DOWNLINK SPECTRUM?

300 -  600 Hz is for initial TUNE up (automatic by the user software)
600        Hz is the PILOT Satelite RYRYRYRY tone
660 -  720 HZ is for AMSAT Bulletins
720 -  780 Hz is for ARRL/JARL/etc Bulletins (just for example)
780 - 3000 Hz is for user QSO's

I can see it now..  Just like 80m, people will start thinking they "own" a
frequency, hi hi...

de WB4APR@amsat.org, Bob

APRS LIVE pages     http://web.usna.navy.mil/~bruninga/aprs.html
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