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*Subject*: [amsat-bb] AO40 tracking at extreme angles: squintdoppler*From*: "nn0v" <nn0v@xxxxxxxx>*Date*: Fri, 26 Oct 2001 23:30:50 -0500

I was just tracking it for fun even with the xponder and rudaks off; the doppler plot to the right of the demod spectrum in ao40rcv is shwoing a z shape, the hz/sec indicator is bouncing between +15.3 and -15.5 hz, valid crc is 28 out of 176(16%), signal is bouncing 13 db, with each rev, 5.76 rpm approx, the doppler from the edge is very pronounced squint at this131 translating to a doppler of 7.67 mph to and fro from whatever is sweeping the rf around. You got gravity on board that thing now! Well just calculating out loud: lets see what we got here. Doppler=veloc*freq/c-Freq/c where c=983,516,160mph. Diameter to generate a speed of 7.67mph where it rotates 5.76 per minute: 7.67mph=11.2493 fps 0.096 revs per sec. and 10.4166 seconds per rev circumference thus 117.18 feet; circumference=2piR. circumference=2pi*r so radius is 18 feet...that isnt possible , so what are we seeing here: Some kind of knife edge difraction moving along the straight parts of the satellite ? So the doppler of the signal is made worse by the shape of the satellite at this sharp angle.like whipping the antenna around or something. It would be nice to be able to measure phase shift vs rotation for various satellite shapes to try to find a more ideal combination. There's plenty of signal from the beacon, its above noise floor even at the bottom of the dip. Well this doesnt add up well, and when the satellite is at better squints I dont think the doppler zig zags are more than a few tenths of a hz. Now that I know what I'm looking for I'll watch for this when its at smaller squint angles and see what the radius of the transmitting antenna looks like in other cases. That must be why nasa always has an s band omni mounted on a stick that juts away from the satellite a few feet, so the edges wont whip the doppler around like that, cause they hate the phase mod it does to the carrier. I guess the triple legged starfish shape would explain this doppler zigzag shape. I know you guys were talking about this before but dont remember seeing any calcs like this.. ---- Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA. To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org

**References**:**Re: smoked it***From:*Jens H. Jensen

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