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Re: PSK31/AO-7 - Hellschreiber alternative.



John

You might try Hellschreiber ( FELD HELL MODE ) as an alternative to using
PSK31. It has a lower duty cycle than PSK31 and tolerates doppler shift much
better. In my experience, the Hellscrheiber mode always worked much better
with satellites. Nino ( IZ8BLY) has a Satellite Mode option in his software
that uses the full-duplex capability of the soundcard and allows
simultanious TX/RX.

I've used PSK31 on AO-40 with a program called WinPSK by Moe Wheatly. The
AFC seems to track doppler well, but it does have it's limits. I did
experiment with with FO-20 and FO29 years ago with the same program. As you
know, the doppler problem is worse as you go higher in frequency and the
70cm downlink of these two LEO sats will make things worse.

Moe Wheatly's WinPSK - http://www.qsl.net/ae4jy/

73, Tony - AA2AE




----- Original Message ----- 
From: "John Mock" <kd6pag@qsl.net>
To: <amsat-bb@AMSAT.Org>
Sent: Monday, December 01, 2003 12:25 PM
Subject: [amsat-bb] Re: PSK31/AO-7


> 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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