john.brewer@us.schneider-electric.com wrote:
Can anyone suggest a workable method of determining the resonant frequency
of a set of traps off of a Cushcraft tribander? I've got a working GDO, but
cannot find a dip with this configuration. Perhaps its my method of coupling
the GDO to the trap. I've just been placing the GDO coil nearby the feedline
end of the trap as it sits on a wooden stool.
Anyone have any tried and true methods for doing this?
Thanks
John
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
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