"Bill Turner" wrote in message
...
I've been following this mind-numbing discussion for days now and still
don't have the answer to the original question:

Bill, I posted an example of me, as a naive ham, reducing the size of my
dipole from 180 feet to 90 feet by adding loading coils. Please follow
that experimental excursion to find out what the discussion is all about.

Is the current the same at both ends of a mobile whip's loading coil?

The mobile antenna is a standing wave antenna. It has a forward current
and a reflected current, both traveling waves, flowing through it.

1. The forward current flowing through the coil is close to the same
magnitude at both ends of the coil.

2. The forward current phase shift through the coil is difficult to measure
but it is NOT zero. It is more in the neighborhood of tens of degrees.

3. The reflected current flowing back through the coil is close to the
same magnitude at both ends of the coil.

4. The reflected current phase shift is close to the same as the
forward current phase shift, i.e. tens of degrees..

5. The standing wave current, the only one measured so far, is the
phasor sum of the forward current phasor and the reflected current
phasor. The magnitude of the standing wave current depends upon
the relative phase between the forward current and reflected current.

To see some variations please visit: http://www.qsl.net/w5dxp/3freq.gif

When one realized that the standing wave current at the bottom of
the coil is 0.1 amp while the standing wave current at the top of
the coil is 2 amps, one comprehends why he must abandon the
concept that standing wave current flows.

From the equation for the standing wave current, cos(kz)*cos(wt),
one can be see that the standing wave current is not a normal current.
This is explained in terms of light waves in "Optics", by Hecht.

6. Since the forward current phasor and reflected current phasor are
rotating in opposite directions, the phase of the standing wave current
is fixed and close to zero degrees all up and down the antenna, from
feedpoint to tip top. Since the phase of the standing wave is unchanging,
it cannot be used to measure the phase delay through a coil. All of the
delay measurements, except the self-resonant frequency measurements,
have used standing waves which are incapable of phase transitions in
the average loaded mobile antenna.

The phase of the standing-wave current is fixed close to zero degrees
until the antenna gets electrically longer than 90 degrees. Then it shifts
abruptly by 180 degrees and remains fixed at that new value for another
90 degrees. This is illustrated in Kraus', "Antennas for All Applications",
3rd edition, Figures 14-4 - 14.6.
--
73, Cecil, W5DXP