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

Re: Mobile antenna question



Bob,

I will not debate your numbers, but only to say I got excellent reception
of AO-51 telemetry using 9600-baud packet audio out of my FT-847 to the
soundcard.  This was using a 1/4 WL mag-mount whip stuck on a square of
sheet steel on my roof.  This was using a good GasFet preamp at the
antenna.  The preamp made the difference.  I had good tlm down to about
10-deg elevation.  I have trees at that elevation so probably as much of
the 'equation' as the antenna pattern.

I do not know how one would use the whip antenna for Tx, too...full duplex,
that is.  My final set up is 11-element UHF yagi + preamp and 3-elements of
my Arrow beam for 2m; full az-el with B5400 rotator.  With this I see S-9
signals...no surprize there.

73's Ed - AL7EB
www.qsl.net/al7eb


At 03:54 PM 1/25/2005 -0500, Robert Bruninga wrote:
>>>> 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
>----
>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
----
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



AMSAT Top AMSAT Home