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Re: Topband: Transmit antenna de-tuning relay.

To: Greg Chartrand <>
Subject: Re: Topband: Transmit antenna de-tuning relay.
From: Herbert Schoenbohm <>
Date: Sat, 23 Mar 2019 14:57:34 -0300
List-post: <>
My tower is a Rohn 45 90 footer and there must be some way of detuning it
via the skirt adjustment means to make it non-resonant at 1825 kHz  This is
similar to electrical towers being detuned near a direction AM station so
their pattern is FCC compliant.   In some cases, the power companies used
some drop wires to get the electrical pole to resonate outside the AM
frequencies range. But we are talking about a pattern shift here and not
reradiated noise.  There must be a way other than moving the RX antennas
250 feet away from the tower.

Herb, KV4FZ.'

On Sat, Mar 23, 2019 at 2:35 PM Greg Chartrand via Topband <> wrote:

>  The best way to isolate the TX antenna for receiving is to have it float
> above ground. The worst means is grounding the antenna. The grounded
> antenna will re-radiate any noise it captures rendering your RX antenna
> useless. It only takes a few PF to ground to make a TX antenna your
> principal noise source so keeping that in mind, deploy the relay(s) such
> that the antenna sees no ground.
> In my case, I have a center loaded vertical, it connects to a L network
> matching circuit; the isolation relay opens the wire going to the vertical
> so it floats well above ground. It can get tricky is you have a grounded
> shunt fed tower, however, I found floating the shunt wire works as well as
> anything.
> The best test for finding the best isolation strategy is to take an AM
> radio tuned as high as it can go and put it in as close as you can to the
> vertical. You should hear the re-radiated noise make the radio blast noise.
> Now you can test grounding (if you don't believe me), floating,and even
> de-tuning. BTW I could never get de-tuning to work as well as floating.
> Good luck!Greg W7MY
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