Cecil Moore wrote:

Reg Edwards wrote:

A 100 turn coil, 10 inches long, 2 inches in diameter, has an
inductance of 102 microhenrys, a Q of aproximately 380 at F = 1.9 MHz,
and the self-resonant frequency is 12.0 MHz.


I'll bet the measured self-resonant frequency would be lower
if mounted as a base-loading coil on my pickup.

Seems the VF of the coil is 0.041 based on 10" being 1/4WL
at 12 MHz. Assuming that VF holds down to 1.9 MHz we
can calculate the electrical length of the coil on 1.9 MHz
which will be the same as the phase shift through the coil.

So I get about ~14 degrees of phase shift through that coil
at 1.9 MHz assuming the self-resonant frequency really
is 12 MHz at the spot where the coil is mounted.

If the coil were used on 3.8 MHz, the phase shift would
be ~28 degrees.

But my 75m bugcatcher coil shows to be self-resonant at
6.6 MHz while sitting there on my pickup being driven
by an MFJ-259B. It is 6.5" long. When 6.5" is 1/4WL
at 6.6 MHz, the VF = 0.0145, considerably lower than
the coil above and operating much closer to its self-
resonant frequency.

A length of 6.5" coil with a VF of 0.145 on 4 MHz is
~55 degrees of phase shift. And indeed the net current
at the top of the coil drops to about 2/3 of what it
is at the bottom.

Ok, I have had a thought. And I had to go back to where everyone,
starting with Cecil, was talking about or responding to a constant delay
through the coil.

Picking a nice round number, say 55 degrees, I would then need 35
degrees of whip above that coil to make a quarter wave resonant antenna,
correct?

So, it should work just as well, using Cecil's reasoning, if I displace
that coil to another position. He did measure the coil as a standalone
device which causes a fixed delay, correct?

Ok, so now I move that coil up the antenna, not much, say 2 degrees.
Now I have 2 degrees below the coil, and 33 above it. It will still be
resonant, right? Now I move it another 2, and another and another,
until it it at the top, with no stinger. With the reasoning I have
heard from Cecil, it will always be resonant.

tom
K0TAR