RadioBanter - View Single Post

March 11th 06, 04:34 AM posted to rec.radio.amateur.antenna

wrote:

Cecil,
You have consistently disagreed with me when I said time delay through
an inductor with tight mutual coupling from turn-to-turn is somewhat
close to light speed over the physical length of the inductor,

No, I haven't, Tom. What you are describing is the voltage delay.
I have never argued with you about the voltage delay through a
coil. It occurs at the speed of light adjusted for VF. In EE101
everybody learns that the voltage leads the current through a
coil. The question is by how much in a 75m bugcatcher coil?

Have you ever seen a graph of the voltage vs current at the
output of a series coil? It shows the current lagging the
voltage by 90 degrees. It takes a series resonant capacitor
to align the current with the voltage again.

rather
than the time it takes current to wind its way around through the
copper.

If you can find a posting of mine like that, I'll give you $100.
If you can't find it, please admit you are fibbing again about
what I have said.

You didn't like my measurement of a small 100uH choke,

I didn't say I didn't like it. You posted some results and then
described those same results differently as time passed. At the
moment, I have no idea what those results were. Was the -60 to
-70 degree delay a voltage delay or a current delay?

and said
a large inductor like a bug catcher coil is different. You predicted
standing waves in that inductor.

Now we are getting to the truth. A 75m bugcatcher is closer to
being a Tesla coil than it is to being a lumped-inductor. It
satisfies R.W.P. King's advice that if the wire length used
to make the coil exceeds 1/6 wavelength then, "an adequate
representation of the reactance of a coil with a nonuniformly
distributed current is NOT POSSIBLE in terms of a coil with
a uniform current". The 75m bugcatcher uses very close to
1/6 wavelength of wire.

And yes, standing wave antennas have standing waves so a 75m
bugcatcher coil is emersed in a standing wave environment.
Quoting Dr. Corum: "Lumped element representations for coils
REQUIRE that the current is uniformly distributed along the
coil - no wave interference and no standing waves can be
present on lumped elements."

I have a 100 turn 2 inch diameter air wound inductor of pretty good
quality. It is 10 inches long.

What is the inductance? What is the Q?

Please tell all of us the time delay you expect in that inductor on 3.8
MHz. Please tell all of us what that delay means for your various
changing theories about waves standing in that coil.

First please describe the circuit used to drive the coil, what other
components are in the loop, and how you are picking off the two currents
at the ends of the coil. Is your Network Analyzer equipped with current
probes? If not, you are wasting your time. We already know the delay for
the voltage will approximate the speed of light adjusted for VF.
--
73, Cecil http://www.qsl.net/w5dxp