[amsat-bb] Re: Turn off AGC when receiving BPSK-1000
bruninga at usna.edu
Thu Aug 18 05:47:44 PDT 2011
[Using attitude control]...
> We could mount microwave antennas on a nadir-facing
> surface and provide consistent, predictable, strong,
> wideband signals to ground stations during a pass.
The problem with LEO satellites is that a nadir facing antenna does give
great gain directly overhead ground stations, but only for about the center
2 minutes of only the one direct overhead pass a day. The problem with
facing antennas "down" on a LEO satellite is that 90% of the users are not
"under it", but to the side of it.
For example, lets say that we put relatively high gain antennas facing down
giving about a 45 degree antenna pattern (say around 10 dB). Now looking at
the total time that ARISSat is above 45 degrees, turns out to be about 3
minutes a day or less than 10% of all the time it is in view to any one
But as you say, it is a great advantage if the objective is to provide a 2
minute comm. window to anyone on the planet once a day, then such a design
does give as much as 16 dB or so advantage over an omni antenna on a
Anyway, just a thought.
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