[amsat-bb] Re: AO-51 mode L/U
Alan P. Biddle
APBIDDLE at UNITED.NET
Thu Nov 27 14:04:08 PST 2008
After you get your computer control working, highly recommended for both you
and the people you work, you will need to tweak or at least verify your
uplink. Most ham gear is pretty good about frequency and stability, but the
local oscillator frequencies may not be quite on, and few hams have digital
counters which are highly accurate at a GHz or so. If accessible, the LO
output can be measured, usually more accurately. Also, the rigs in the
satellites drift a small amount.
What I have done is take advantage of times when I was the only one on mode
LU or LS by changing the uplink by +/- 5 kHz at minimum usable TX power.
Usually one will sound better than the other. So move in that direction 2-3
kHz and repeat, reducing the TX power as needed. You should be able to box
the best uplink frequency quickly. Then you can either change the uplink
frequency in your control program, or adjust the LO frequency stored in your
program. I do the latter. Of course, always be alert for someone else
wanting to use the bird.
I have a system roughly equivalent to Drew's and once I get out of the
horizon clutter it only takes 5 watts or so for full quieting under most
More information about the AMSAT-BB