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Re: Mobile antenna question



>>> Andrew Glasbrenner <glasbrenner@mindspring.com> 1/25/05 11:19:54 AM
>>>
>For true in-motion mobile, consider a 1/4 wave whip for 435, 
>with a preamp preferably.
>I have a feeling someone will pop up and say a 3/4 wave is best...
>that antenna pattern is very high angle...

Yes, it gives worse gain below 20 deg, about equal at 25 and is
3 dB better above 30 on up to 80 deg.  See plot about 80% down
my page:

http://www.ew.usna.edu/~bruninga/astars.html

So if you drive back east and are always in trees except for
everything around you above 25 deg, then use the same 2m
19.5" whip as a 1/4 on 2m and as a 3/4 on 70 cm for better
performance.  BUT of all the times that a satellite is in view, it 
is only above 25 deg less than 30% of the time..

But when it is, you'll be 3 dB better off.

But previous mode J birds had such low pwoer that
the 1/4 couldnt hear it reliably at the horizon anyway
(its 6dB further away) so having better 1/4 performance
down below 20 deg where you can't hear the bird anyway
is a moot point.

But if ECHO is going to operate at higher power, then
maybe you can hear it lower and therefore you want
the 1/4 wave for better longer access times though
not as good performance closer in...

Like anything, there are tradeoff's 

I'd put both on the car and switch!

de WB4APR, Bob
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