Tom Donaly wrote:
I know you're champing at the bit to claim my test setup was all
wrong and that I used standing wave current when I should have
been using traveling wave current, and all that, but you'll just
have to wait.

That's not true at all, Tom. It's a trivial procedure
to use standing waves to determine the approximate 1/4WL
self-resonant frequency. But as with 1/4WL monopoles,
there is *NO 1/4WL self-resonant frequency* without a
ground plane or counterpoise and the quality of the
ground-plane/counterpoise has an effect on the self-
resonant frequency. Sorry, I don't have anything
approaching a perfect ground plane for 4 MHz.

I suppose one could use two identical coils and turn it
into a dipole but I don't have another 75m Texas Bugcatcher
loading coil.

Let me say once again: A 1/4WL monopole, all by itself
in free space is *NOT resonant*. After all, making guy wire
segments 1/4WL long is one way of breaking up their resonance.

We are not looking for super high accuracy/precision/resolution
here. Almost everything is an approximation because we don't
share exactly the same test environments. All I am after is
the technical truth - there's nothing personal involved.

Neither is a 1/4WL coil self-resonant all by itself in free
space. I don't know what Reg was thinking if he advised hanging
the coil from the ceiling without a counterpoise.

A traveling wave can be used to determine 1/4WL self-resonance
but it is a little more complicated than using an MFJ-259B
with standing waves. A load resistor minimizes reflections
while current probes are used to measure the phase shift through
the coil. When the phase shift is 90 degrees, that's the 1/4WL
self-resonant frequency.

I'll tell you what, Cecil. If you'll test your coil, and
describe how you did it, I'll tell you what I did. Fair?

1. I connected my 75m Texas Bugcatcher coil through about
a foot of wire to the bumper mount on my GMC pickup and
connected my MFJ-259B to the coax connector under the
bumper. I tuned for lowest impedance above 4 MHz. The
1/4WL self-resonant frequency was ~6.6 MHz. These
measurements were done and reported in March, 2006.

2. I used a tri-mag mount sitting on the hood of my GMC
pickup fed through ~6' of coax. The 1/4WL self-resonant
frequency was ~6.9 MHz.

3. I used a traveling wave on top of a wooden bench and
found the frequency at which the phase shift through the
coil was ~90 degrees. That frequency was ~7.2 MHz.

4. I modeled the coil with EZNEC and got some segmentation
length warnings. EZNEC reported the 1/4WL self-resonant
frequency to be 7.96 MHz.

The spread in the above frequency figures is about +/-8%.

Again Tom, the only thing I am after is the technical
truth. If that is also what you are after, we should
have no personal conflicts.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com