[TowerTalk] Loading a Pro-AM 160M on other bands?

Cecil Moore w5dxp at hotmail.com
Fri Feb 16 13:50:09 EST 2007

>From: kd4e <kd4e at verizon.net>
>Subject: [TowerTalk] Loading a Pro-AM 160M on other bands?
>Date: Fri, 16 Feb 2007 12:03:31 -0500
>Is the coil and feed system on such a vertical
>such that trying to load it on 80, 40, 20, etc.
>via an antenna tuner is a waste of time?

Every loading coil has a self-resonant frequency somewhere above the
frequency it is used on for mobile operation. It occurs at the frequency
where the distributed capacitive reactance is equal to the inductive
reactance. A mobile loading coil should not be operated at or above
its self-resonant frequency. As a data point, my 75m bugcatcher coil
is self-resonant around 6 MHz, making it not useful on 40m.

160m loading coils are large with lots of distributed capacitance. Odds
are, they are all self-resonant before the 80m frequency is reached
and certainly before any of the other HF frequencies. So, to answer
your question, operating a loaded mobile antenna far above its resonant
frequency is usually an extreme waste of RF energy.
73, Cecil, w5dxp.com

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