[amsat-bb] Re: Turn off AGC when receiving BPSK-1000

Bob Bruninga 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
ground station.

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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