[amsat-bb] Re: PSK31/AO-7

[John Mock <kd6pag@xxxxxxx>]

I'm not a signal processing wizard, but i'll hazard a guess.  Since we
hear the beacon FM'ing a lot when there's a strong signal elsewhere in
the passband, PSK31 may not work very well if there's SSB or CW active on
AO-7.  I think PSK31 depends on the carrier frequency being relatively
fixed and it extracts the data from deviation from that carrier.  Since,
at least in the implementation i looked at, it uses a phase-locked loop
to track the carrier, it ought to tolerate modest amounts of doppler (but
perhaps not as much as one might encounter when a LEO goes overhead).  If
the whole passband is shifting around, as it does on AO-7 on a routine
basis, then the carrier is going to be shifting around, too, faster than
an ordinary PLL can track.  So i doubt PSK31 is going to do very well on 
AO-7.  Even one CW operator running a little extra power because he can't 
hear well might be enough to throw off PSK31 decoding.

On the other hand, i'm a little surprised it's not working well on AO-40.
Anyone tried it on the Fuji birds?
				     -- KD6PAG
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