Walter Maxwell wrote:
Cecil, I suggest you re-measure the self-resonant frequency of the coil by
itself, and if you have the means to do it, also measure the series resistance
at both the self-resonant frequency and at 4.0 MHz. I'm betting there will be a
large difference in the resistances, and that the self-resonant frequency will
be much greater than 6.6 MHz.

I'm not sure how to measure the 1/4WL self-resonant frequency
with an MFJ-259B without a ground plane. I suppose it could be
done using a 1/4WL counterpoise in free space. Let me just
report what the MFJ-259B readings are with the isolated 75m
Texas Bugcatcher coil across the MFJ-259B terminals.

The first dip in impedance is at 14.7 MHz where the MFJ reads
620+j0 ohms. The second dip in impedance is at 24.4 MHz where
the MFJ reads 88+j0 ohms. Is the first dip the 1/4WL self-
resonant point and the second dip the 1/2WL self-resonant point?

I want to make it clear that the previously reported 6.6 MHz
self-resonant measurement was made with the base-loaded coil
mounted a few inches away from my GMC pickup ground plane. The
ground plane was no doubt in the field of the coil at the bottom
end so the coil was certainly not isolated as it is in the above
reported measurements.
--
73, Cecil http://www.qsl.net/w5dxp