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Re: Crosstalk on Mode B



Hi Scott,

The coax can be run perpendicular to the antenna elements on a
linearly-polarized antanna with no interaction. On CP antennas there is
nothing perpendicular to the rotating E-field so you just have to keep the
coax as far away as possible.

It sounds like the 435 MHz signal could be overloading the preamp. A
2-meter/70-cm antenna diplexer installed ahead of the preamp should solve
that problem. Leave the 70-cm port open. The loss is low enough (0.1-0.2 dB)
to be neglected on 2 meters.

73,

John
KD6OZH

----- Original Message -----
From: "Scott Townley" <nx7u@arrl.net>
To: <amsat-bb@AMSAT.Org>
Sent: Sunday, 15 July 2001 19:51 UTC
Subject: [amsat-bb] Crosstalk on Mode B


> I still have some crosstalk problems on Mode B.
> My setup is pretty marginal so no doubt that contributes:
> 10' tripod
> 12' yagis (linear, both vertical) on wooden crossboom about 6' separation
> I run the coaxes down the yagi booms to the crossboom, then across to the
> mast and then down the mast (as an aside, why does it seem more common to
> droop the coax off the back end of the yagi?).
> 2m GaAsFET preamp on the mast (about 10' of RG-8/U foam in front).
> The antennas are rarely in the same spot in the yard twice, as I put them
> up and take them down just about after each use (XYL restrictions, you
> know...)
>
> One thing of note is that the antennas are placed fairly near (within 8'
or
> so) of trees and a cinderblock wall about 6' high.  I notice that
depending
> on how I steer the antennas in azimuth, it seems to change the probability
> of crosstalk.  I say "probability" because as yet I have not been able to
> divine any pattern to it, just that sometimes it's there and sometimes
it's
> not.
>
> Is this a simple "2m Bandpass Filter" RF overload kinda issue, or is there
> more here than meets the eye?
>
> Thanks In Advance,
> ------------
> Scott Townley
> nx7u@arrl.net
> Gilbert, AZ  DM43
>
> HF/VHF/UHF/Satellite MOBILE station
> http://www.primenet.com/~nx7u
>
> ------------
> "When the Going gets Weird, the Weird turn Pro"
> Raoul Duke, Sportswriter
>
> "Don't worry Boys, we'll weather this Storm of Approval and come out as
> Hated as Ever"
>
>
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