[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

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:


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
Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
Not an AMSAT member? Join now to support the amateur satellite program!
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org