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Mode U/S passband frequency alignment



I was on AO-40 for the first time last night (Monday 10/29/01) around 7:30
PM (2330 UTC ?) using Mode U/S. I spent at least 15 minutes trying to find
my down link frequency. Once I did I noticed I was off about 15KHz from
where I expected to be based on my up-link frequency and Doppler, which
should have been less than 1 KHz at the time per WinOrbit.

The question I have is what is a known good, and accurate, down-link
frequency for a given up-link frequency with no Doppler shift? I understand
that the oscillators will drift a bit on the on-board transmitter and
receivers, but I don't expect it to be nowhere as great as the 15 KHz or so
I experienced. I also plan to try calibrating my UEK3000 down converter so I
have a better idea what "S band" frequency converts to what "2m" frequency.
Once I have that I should be in a much better position to find my down-link
next time without having to hunt up and down the passband 10's of KHz
looking for it. For a newbie that was the difficult part to start with since
at one point I didn't even know if I was even getting in to the bird! I was
about ready to give up for the night.

For the two stations I did make contact with last night, thanks - it was
great, even if I didn't get a complete callsign of the other station. I'm
still trying to get  a better S/N ratio, or better DSP to clear up the audio
on my end.

My current station setup is as follows:

BBQ grill dish antenna for 2.4GHz 24dbi gain with linear dipole feed
M Squared 70cm 11 element yagi at 13.3dbi gain linear (420-50-11)
UEK3000 down converter
Yaesu FT-847 with an InRad 2.1 crystal RX filter, and a Collins TX filter

Both antennas are mounted on their own separate camera tripods that sit
outside on the grass, next to my ground floor apartment. I have to feed the
coax cable through the wall next to an in-wall air conditioning unit to get
outside from my radio. I use a FT-817 to manually tweak the down-link
antenna, on the MB frequency from outside, then reconnect the coax to the
rig inside to operate. I found I normally need to move the down-link antenna
only every 30 to 45 minutes to keep the signals peaked. That's the nice
part, I don't need any expensive tracking rotors.

Leland C. Scott
KC8LD0

Saw this on a Tee-shirt:

"I am a bomb technician. If you see
 me running, try to keep up. "

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