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[aprssig] ARISS Satgates

Robert Bruninga bruninga at usna.edu
Tue Jul 20 15:06:01 UTC 2004


>>> jdw at eng.uah.edu 7/20/04 10:52:47 AM >>>
>> More ARISS Satgates needed?
...
>Would a simple quarter wave be better than a vertical 
>antenna with  gain, because of the null above the gain 
>antenna?

Yes, the 19" 1/4 wave is better for several reasons.
1) It has better elevation coverage then the typical
    half wave or 5/8 wave antenna
2) The 5/8ths has gain only below about 15 deg where
    usually the satellite is not decodable because of
    6 dB greater distance and trees and inabilty to see
    down to the horizon anyway...
3) The 19" whip is also resonant on the 435 MHz 
    providing dual band operation.
4) On 435, the 19" whip is a 3/4 wave antenna and has 
    almost 7 dBi of gain above about 25 deg up to about
    70 deg
5) No need to worry about the overhead null of the
    19" whip which is good to above 60 deg, because
     any LEO satellite is only above 60 deg less than 4%
     of all possible access times...

To see the TIME versus ANGLE plot and see why
elevation rotators are NEVER needed for LEO satellites,
see:  http://www.ew.usna.edu/~bruninga/rotator1.html

Bob, WB4APR

thanks,
Jason
kg4wsv


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