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Re: PSK-31 MFSK Hell via AO-10

> I wonder if you've tried MFSK or Hellschreiber via AO-10? I'm sure by now
> you've found that PSK31 dosn't like doppler much hi. Hellschreiber ( Feld
> Hell ) is much more tolerant to doppler... in fact I've used it
> 70cm downlink! When compared to other modes, it has the least impact onthe
> satellites power budget because of it's low duty cycle, about  23%.
> as sensitive as the other modes but if they won't print due to doppler,the
> extra sensitivity won't help any Hi.
> I recently experimented with MFSK vs PSK31 and I can tell you that neither
> is very tolerant to doppler but MFSK16 can print substatially better at
> times. I conducted my experiments by copying my own downlink using two
> instances of G3PLX's PSK31 software one for TX the other for RX and didthe
> same for Nino's MFSK. This allows you to use the full duplex capability of
> your soundcard allowing simultanious TX and RX via Satellite. It's
> testing different power levels modes etc.

Tony, Peter, Tom,

The limitations of PSK31 with doppler shift is not a fundamental limit with
DPSK but rather a limitation imposed by the PSK31 application programs.  On
HF, an aggressive AFC is bad due to all the interference and signal
congestion.  The typical limit imposed with most programs is about
1-2Hz/Sec.  As a little experiment, I changed the AFC filter constants in
WinPSK and was able to track 20Hz/Sec psk31 signals.  I'm not a satellite
guy so don't know what the typical doppler shift rates are so don't know if
this is enough.  Much more than 20Hz/sec and the AFC loop gets more tricky
and you also have the issue of running outside the audio bandwidth during a
QSO and having to retune the receiver.

If there is any interest in pursuing a satellite version PSK31 program let
me know.  It would also be easy to make a full duplex version for monitoring
the downlink, assuming most operators have a PCI duplex soundcard. There
just wasn't any need for duplex on HF so it was not enabled.

There was also a question about feedback of received audio back onto the
transmit audio.  You should be able to mute the Line-In or Mic-in controls
in the PLAYBACK mixer control.  This does not inhibit the Recording Line-in
or Mic-in from working during receive but does keep it from looping back
into the line-out or spkr out.


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