[amsat-bb] Re: probably simple

Andrew Glasbrenner glasbrenner at mindspring.com
Thu Jan 7 21:30:44 PST 2010

> But any pass where you are really stretching the footprint is going to 
> be a low elevation pass.  The more you stretch, the lower the pass.  
> In the limit, I think Bob's ultimate pass has a peak at .001-degrees 
> for both stations.  If you're doing that, then you're at TCA, and zero 
> doppler.
> That's all I meant to convey,
> Greg  KO6TH
I understand, but with all due respect your assumption is incorrect that 
long distance QSOs are always at TCA and zero Doppler, even 
theoretically . This is only the case when the two stations are at near 
right angles to the track of the satellite.

Use the following example. If I want to work LU5BOJ/O in FG75 from EL88 
on HO-68, my only windows are at either LOS or AOS, depending on whether 
it is an ascending or descending pass. Neither pass will be a low pass 
for either station, and neither QSO will occur at TCA or zero Doppler.

In Bob's case, let's look at his next possible window with Paul, 2E1EUB 
in IO92. Bob is in CN76. At the beginning of the 1 minute window 
tomorrow at 1251Z, Bob's Doppler shift on 432 is -3.68 khz.

On the next mutual window at 1452Z, the beginning Doppler is -7.93 khz. 
On the next, at 2020Z, it's -8.3 khz. None of these windows are over 2 
degrees elevation, and none are at TCA for either station.

When you have 60s to make the QSO, being right dead on frequency is 

Drew KO4MA

More information about the AMSAT-BB mailing list