[amsat-bb] Re: [psk31] PSK31 Satellite Uplink on 10m (final plan?)

[Bob Bruninga <bruninga@xxxxxxxx>]

Peter and other PSK-31 authors?

I wonder, now that we have now discovered that the 1 or so Hz per second
of Doppler shift on the proposed 10m PSK satellite in LEO orbit is not
much different from that experineced on the very high altitude AO-40
satellite, I wonder if it is time for authors to consider including a
little bit of selectible downward AFC in their programs? (or maybe its
fully there now?)

We are not talking about full doppler prediction of satellites, but simply
a "satellite" button on the PSK-31 control panel.  When this button is
pushed, it tells the PSK-31 demodulator to "expect" on the order of about
1 Hz per second DOWNWARD movement of frequency.  It may go as high as 2 or
3 hz per second (i'll have to calculate that), but that is only during the
worst case which only happens about 10% of the pass.  The rest of the
time, the rate of change is much more well behaved.

INFACT, the AFC can simply watch itself and REMEMEBR its rate of change
and simply continue with that same prediction, updating itself as it goes.
Thus there is never any need to "track or predict satellite detail motion,
just let the AFC be built to anticipate smoothly decreasing frequency at a
very slowly changing rate-of-change.  All on the order of about 1 Hz per
second or so..

BUT!  It should be noted that PSK or other full carrier modes are not
generally "desired" on the analog Satellites, though I think it can be
argued that due to the DSP gain of QRP PSK, that the net power demands of
a low power PSK-31 user is probably less than the power required for an
SSB signal.

THe problem being that of insuring that users use no more power necessary
for communications.  In that case, I am sure that the AMSAT community
would not object to PSK-31, but all it takes is one guy who can't hear
(Its harder to hear AO-40 than to transmit to it), to  crank up 100W on
the UHF uplink pure carrier and upset everyone.

Good luck...  I'd love to see some experiments to see what is the minimum
power necessary to make AO-40 on PSK-31..

Hummh... Bob

Date: Thu, 21 Nov 2002 06:05:58 -0500
From: Jeff Griffin <kb2m@arrl.net>
To: Bob Bruninga <bruninga@usna.edu>
Cc: psk31@bipt106.bi.ehu.es
Subject: Re: [psk31] PSK31 on Ham Satellites

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>But it wont work because of the 60,000 hz of Doppler
>shift experienced on the 2.4 GHz downlink.

About a year ago or so ago, a group of us(about 5 or so) ran PSK31 for
several weeks on AO40. The doppler was troublesome but after a little
practice QSO's were possible without too much trouble. In fact it ws a lot
of fun working PSK31 with the doppler....

73 Jeff kb2m

de WB4APR@amsat.org, Bob

PCsat WEB  page     http://www.ew.usna.edu/~bruninga/pcsat.html
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