[amsat-bb] Re: Sat antenna fixed elevation -- how many degrees is the best?

Robert Bruninga bruninga at usna.edu
Tue Feb 19 15:37:05 PST 2008

>> I've seen people with fixed elevations of 25, 
>> 30, 35 degrees, any consensus on which is the best? 

No more than 10 or 15 degrees above the lowest horizon you can
See http://www.ew.usna.edu/~bruninga/rotator1.html

>> And how well, if at all, does an antenna with a 
>> fixed elevation of 30 degrees or so perform when 
>> the sat is higher than 60 degrees?

Doesn’t matter.  Satellites are only above 60 degrees less than
2% of the time and then they are 10 dB closer and so strong you
don’t need any gain.

> Determine your beam width, divide by two, and 
> that is your EL.  I would tend to favor the 
> horizon, obviously the greatest range.

That approach would make the gain at the horizon (where it is
needed most) be always 3 dB down.  And it would give maximum
gain (at 30 deg) where it is needed least (where the satellite
is already 6 dB stronger).

Remember, any LEO satellite spends 70% of all access time below
22 degrees or so, and so having maximum gain down on the horizon
is most important.

> By experiment, I determined the beamwidth ~65°, so I fixed EL
at 30°.

That's giving up 3 dB at low elevations where the satellite
spends the majority of its time.  It would be better for a lot
more of the time if it was no more than 15 degrees abouve your
lowest horizon. IMHO


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