Morning,

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 above.

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?

Alan WA4SCA