RadioBanter - View Single Post

March 15th 06, 11:17 PM posted to rec.radio.amateur.antenna

wrote:
Probably, since it appears you are the only one finding fault with
them.

Tom Donaly hasn't even posted any results yet. How could I
possibly be finding fault with them?

It appears you have painted yourself into a corner by trying o apply a
paper about Tesla coils that specifically states it applies only to
inductors at self-resonance to inductors operating away from
self-resonance.

Quoting from the previously referenced paper: ".. is an approximation ...
appropriate for quarterwave resonance and is valid for helices with
(5*N*D^2)/lamda 1. N is the turns/inch, D is the diameter of the
coil, and lamda is the self-resonant frequency. That calculation
for my 75m bugcatcher coil is ~0.4 so it meets the criteria.

The VF calculation of 0.175 is therefore valid. There is no valid
reason to suspect that the VF wouldn't hold approximately down to
4 MHz and below. There is no warning of such abrupt shifts in the
VF anywhere in the article. And Dr. Corum's VF equation is close
enough to my rough earlier estimate of 0.15 to be acceptable.

you'll see time delay is essentially flat except near the 16MHz
self-resonant frequency and a higher-frequency resonance at 26 MHz.

But cos(kz)*cos(wt) is what is being measured. That signal has zero
phase shift from tip to tip in a 1/2WL thin-wire dipole. It cannot
be used to measure phase shift because it is incapable of a phase
shift through 180 degrees of wire or 180 degrees of coil. It only
changes phase every 180 degrees of a wire or coil.

What is happening in the above measurement is that when the coil
is more than 1/2WL, the phase of the standing wave current suddenly
reverses from close to zero to close to 180 degrees. This is all
explained in Kraus', "Antennas for All Applications", 3rd edition,
Figure 14-4 and is perfectly understandable. The phase of the standing
wave current changes from zero to 180 degrees every 1/2WL. I've seen
exactly the same thing in my experiments just as Kraus predicts and
it supports my side of the argument.

The standing wave current, which has unchanging phase, cannot be
used to determine the phase shift in a wire or coil. A
signal with a cos(kz)*cos(wt) equation doesn't change phase
with variations in 'z'. How can it possibly be used to detect
phase changes in the 'z' dimension?
--
73, Cecil http://www.qsl.net/w5dxp