[amsat-bb] ISS: L band repeater 1354 UTC pass over SE US

Fri Jan 2 06:54:31 PST 2009


>From a technical standpoint, had the best pass ever here.  AOS at 295
degrees, 12 degrees elevation, slant range 1000 miles (1600 km).  LOS at 150
degrees, 6 degrees elevation, 1570 miles (2500 km).  Both are at or near my
local horizon.  This pass was qualitatively different in that I did not
notice a single dropout, and it required modest power even at extreme range.
100-200 watts ERP compared with the 2500 needed on some passes.

One thing I did was recheck the deviation of my transmitter yesterday.  I
had noticed in previous passes that when I spoke, I would _sometimes_ lose
the downlink, and it came back when I stopped.  That is indicative of over
deviation, and/or a really marginal signal at the ISS.  I had set the
deviation years ago at 3.2 KHz, and have gotten nothing but good reports on
terrestrial and satellite communications.  Rechecking, I found that it had
drifted up to 3.8 KHz.  That is well within normal parameters, but I dialed
it back to 3.2 KHz again.  I did not have time to do any A/B testing, but at
least what I did was not harmful.

>From a communication standpoint, not so much.  I did hear someone else bring
up the repeater, and caught "N5???" twice, but each time the repeater
dropped after the first two syllables.  N5UXT???

I have a couple of things to test should they do this again.  My lessons
learned are that: 

(a) You MUST be on frequency, much closer than when operating through normal
satellite repeaters.  The usual manual tuning just does not work in
practice.  It is good to check the actual mode L output, however you get
there, since 2-3 KHz error is critical.  My TX transverter has a few KHz
error in the LO, but I just put the measured numbers into SATPC32, and it
does the correct tuning for me.

(b) Your deviation needs to be optimum, with less being better than more.

(c) You need significantly more power than the usual mode UV or VU, but not
unreasonable ERP.

Thanks to NASA and the ARISS team.  Lets do it again sometime.


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