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Re: [TowerTalk] How to check trap resonance

To: Roger D Johnson <n1rj@adelphia.net>
Subject: Re: [TowerTalk] How to check trap resonance
From: Roger D Johnson <n1rj@adelphia.net>
Date: Wed, 16 Feb 2005 10:48:34 -0500
List-post: <mailto:towertalk@contesting.com>

In the dark recesses of my memory, I remember seeing an article about
determining trap L/C values by using an RF bridge to take measurements
of the trap above and below the traps resonant refquency. Once the L/C
values are determined, the resonant frequency can be calculated.

Many years ago, I wrote a BASIC program to determine the L/C values to
resonate an antenna on two bands simultaneously. I used it with a 3/8
wave vertical on 160 and 80m. I used a modeling program to determine the
reactance required at the antenna base for each band. These values were
plugged into the program which would then  calculate proper the L and C
values. The result looked like a parallel resonant trap but didn't
operate that way. I think Butternut uses the same technique with their
antennas.

I think the program could be modified to operate in reverse. Knowing the
reactance values above and below Fr, the L and C values could be
calculated.

73, Roger

Unfortunately, the coffee hadn't kicked in when I typed the above. It occured to me that my program is just fine "as is". You measure the X values above and below the trap resonant frequency and input it to the program along with the frequencies and it will give the L and C values for the trap.

I also found this site with some more data:

http://www.smeter.net/antennas/notatrap.php

73, Roger

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