[amsat-bb] PSAT and Bricsat FM PSK on same frequencies
tjschuessler at verizon.net
Sun May 24 04:00:03 UTC 2015
Okay so I am a bit confused about how this will work with two satellites both using FM modulation on the same frequency. FM has the capture ratio effect which basically means that if one signal is about twice as strong as the other that signal will capture the receiver and the other one may make a little background noise but won't be properly demodulates. If both of them are received at the same power level pretty much you just get noise a.k.a. SO-50 on a crowded day. So if these two satellites are transmitting simultaneously whichever one happens to be stronger at the moment will capture the receiver. Regardless of whether one of them has a audio frequency modulated on the carrier at 315 hertz while the other ones at 375 you're most likely going to not here both of them simultaneously Heard or displayed on a PSK waterfall.
This may not be an issue in the future as the satellites drift apart from each other but right now as it seems to me they are pretty darn close so if they were both on they would be in the beam width of any directional antenna.
Aside from the frequency of the PSK carrier itself as modulated on the FM, I would also have to assume that the call sign of the PSK data beacon is hopefully different. The PSK I decoded this morning had a beacon call sign of W3ADO-5. I would have to assume there is a different beacon call sign for both. In my reading I have not seen what the difference between the two would be.
Looking forward to soon trying to test an uplink on 28.120 and see if I can hear myself. This looks like a good challenge.
73. Tom. N5HYP
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