[TowerTalk] How to check trap resonance

[Roger D Johnson]

> 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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