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Re: PK96



Jordan wrote:

> Also, is FSK more or less standard
> for now and in future at higher baud rates? Many thanks for your time!

9600 baud FM FSK is sub-optimal in several ways, but makes good use
of available more-or-less unmodified voice-grade radios and the FM
downlink is fairly resistant to Doppler. Going faster eliminates
the "unmodified" part...

FSK isn't the only answer. For example, the NOAA HRPT weather
satellite signals use plain old BPSK at 665.4 kbps. A sneaky
trick is to only partially suppress the carrier, leaving enough
residual carrier for a PLL demodulator to lock on to and track
the signal through LEO Doppler at 1.7 GHz. This sounds pretty
fearsome, but the signals are actually relatively easy to receive.

Some of the fastest amateur digital systems use BPSK - have
a look at the stuff (due to S53MV) documented at
http://www.hamradio.si/psk23cm.html

Short answer: when satellites are launched these decisions will
have to be made. If nothing else, by keeping as much of the
modem as possible in software it can be changed. I'm looking
forward to experimenting with this on P3D - an analogue bent-pipe
transponder will send back anything you throw at it...
-- 
Laura Halliday VA3LDH    "Laisse le vent tout emporter..."
Grid: FN03gs                - Foly/Viennet
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