[amsat-bb] Re: [psk31] PSK-31 Satellite Donwlink Opportunity?

[Bob Bruninga <bruninga@xxxxxxxx>]

On Mon, 26 Feb 2001, Peter Martinez wrote:

> it could work to cancel Doppler shift, but I don't think his proposal
> for an inverting in-band transponder will do this.
> 
> [also] amateurs will be unable to "listen-through" on the same band as
> they are transmitting, and so will not be able to "net" on the same
> frequency as the other station.

Ah, another very good point.  So if the INBAND is not such a great idea,
then maybe 15 meters UP and 10 meters down. This solves many problems:
1) users can operate full duplex
2) The satelite diplexer is much easier
3) COmbined worst case doppler is still under 1 KHz or so
and the Pilot tone and SEEK process I posted in my previous message will
allow the PSK-31 code on the ground to do all the doppler compensation
without ever tuning the RF receiver?

> There is perhaps a case for a non-inverting in-band transponder to
> overcome this. The conversion frequency will be low (1.4 MHz) and
> suffer negligible Doppler. In the case of a PSK31 transponder, all
> stations would set their transmitter and receiver  frequencies split
> by precisely 1.4 MHz (or whatever the actual conversion frequency of
> the satellite was) and work with the PSK31 software running
> co-channel simplex. There would still be the basic Doppler problem,
> but at least if you call a station on the same audio frequency as you
> receive the end of his call, he will hear the start of your reply on
> the same audio frequency as he was transmitting.

Yes!  And this could work as well using a 15 meter and 10 meter cross
band...

de WB4APR, Bob

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