[amsat-bb] SSB uplink to AO-51 on 2 meters and 1268 MHz

OZ1MY oz1my at privat.dk
Sat Oct 28 05:56:32 PDT 2006

Hi all,
>From Monday AO-51 will be in SSB mode on the uplink like
it has been before.

October 30 to November 6
Cross Mode Repeater, V(SSB)/U(FM)
Uplink: 145.880 MHz USB
Downlink: 435.300 MHz FM

Those of you who have tried it before know that you must hit
the frequency correct to get a good downlink signal.
If you use automatic doppler shift correction from your tracking
program it is a little bit easier.

Personally I use SatPC32 to do the correction with the following
line in the doppler.sqr file:

AO-51,435300,145879.25,FM,USB,Nor,0,0,Voice V/U

This worked very good last time we had this mode running
on AO-51. Your transceiver may need small adjustments
to the uplink frequency.

The coming week can be used to get the feeling for running
SSB up to AO-51. The experience gained will be needed
when AO-51 is the new mode with L-band SSB up in
That is going to be very interesting since the doppler shift will
be very fast with this much higher uplink frequency.
The rate of change of frequency will be something
like 340 Hz pr. sec. Worst Case.
Of course it will be less most of the time so that it
might be possible to do the tuning by hand.

December 8 to December 11 New Mode!
Cross Mode Repeater, L(SSB)/U(FM)
Uplink: 1268.700 MHz USB
Downlink: 435.300 MHz FM

I ran some tests on HITSAT. It has a Worst Case rate
of change of approximately 300 Hz. pr. sec. since it
has a perigee of 290 km. That is not easy on close passes.

Lessons learnt :

Make sure the PC clock is correct within 0.1 s
Make sure your position is correct (a friend with a GPS receiver helped on
that one)
The keplerian elements must be correct ( difficult to control)
The tracking program MUST use SGP4/SDP4 (I tested with an older program with
PLAN 13 and that was up to 2 kHz off)
Your transceiver/PC/tracker combination must be able to update once every
0.1 s or faster (special version of SatPC32 in my case)
Frequencies must be correct in the PC or possible to correct on the fly

Then there are frequency drift of the satellite, your transceiver and so on

This means that you must update the keplerian elements at least once
a day. Unfortunately this is not necessarily a guaranty since the keps
are "bad".

Synchronize the PC clock before each pass.

Lessons learnt are about using automatic full doppler tracking. If you
use manual frequency correction try it on the low elevation passes first.

The mode has never been tried before therefor it is very interesting
to see how it will work.

Hope to hear you on AO-51 mode-L(SSB)/U(FM).

Thanks to Colin, VK5HI, and Erich, DK1TB, for help with
the doppler correction.

73 OZ1MY

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