[amsat-bb] Re: I hear WA4SCA calling CQ via ISS
Alan P. Biddle
APBIDDLE at UNITED.NET
Mon Dec 29 08:06:45 PST 2008
Had a great QSO with myself on the 1520 UTC pass. I mostly did some
checking of the home equipment, but have some general thoughts on this mode.
As background, I can get about 50-60 watts to my M2 23CM35EZ linear beam,
rated at 18 dbd.
In comparison with AO-51 L modes, as expected there is little or no "spin
modulation." Obviously the ISS isn't spinning (!!!) and the ISS CP antenna
took care of orientation issues with my beam. I quick BOTE calculation
shows that the shorter path loss due to the lower orbit more than
compensates for the 3 db polarization mismatch. On the other hand, I had to
hit it much harder to get in at all. I am _guessing_ that the squelch is
set tight. (I had full quieting, even when running just barely enough power
to bring up the repeater.) With AO-51 I can work horizon to horizon with
_much_ less than full power, usually 5-10 watts, and a watt or so on an
overhead pass. With the ISS, I needed almost everything below 5 degrees,
though I have a messy, attenuating local horizon. At TCA it still took 5
watts or so to break the squelch. Considering the lossy feed line on the
ISS, my qualitative feeling is this is all in the ballpark.
One thing I did determine is that the uplink frequency needs to be properly
centered. On AO-51 I can go +/- 5 kHz and still get it, whereas with the
ISS I got nothing, even around TCA. +/- 3 kHz is probably more like it, and
of course depends on your power. Probably the RX bandwidth to the ISS rig
is narrower, and of course the signal strength is down for reasons discussed
I know this is out there, but does anybody have off the top of their head a
reference on the ISS antenna orientation, and what its view is WRT the
direction of flight?
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