RadioBanter - View Single Post

March 11th 06, 07:14 PM 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, rather
than the time it takes current to wind its way around through the
copper.

I think I have figured out your misunderstanding here, Tom.
I *never* said the current winds its way around through the
copper. That was just another one of your strawmen that
I don't believe and have never believed. I have offered you
$100 if you can find where I ever said that. Would it make
any difference if I offered you $1000?

The effect of a velocity factor of 0.015 may seem to you
to be the same as "current winds its way around through
the copper" but I assure you, if you understood the wave
model of distributed network analysis, you would understand
why that is not the case.

I can fully understand why someone so emotionally
attached to the lumped-circuit model would assume
"current winding its way around through the copper"
but that is simply a misconception of yours.
Distributed networks are not nearly as simple-minded
as your lumped-circuits.

A helical coil structure with a VF of 0.015 *is what it
is*. Waves propagate at 0.015 the speed of light and
that's quite a delay through a relatively physically
short coil. If the coil is 6.5 inches long, as is my
75m bugcatcher coil, it occupies an electrical length
of 6.5"/.015 = 433" = 36 feet. The fact that it consumes
42 feet of wire is just a coincidence. The 6.5" coil
replaces aabout 36' of straight wire. From those facts,
you can calculate the number of degrees or percentage
of a wavelength.

Shirley, you understand that 1/4WL of a transmission
line with a 0.9 velocity factor is longer than 1/4WL
of line with a 0.66 velocity factor. That's why coax
stubs are shorter than 450 ohm ladder-line stubs. (I
feel like I'm doing a EE323 tutorial here).

What is it about a VF of 0.015 that you don't understand?
All it means is that RF through the coil is traveling
at 1/67 the speed of light. If you understand that
RF through RG-8 is traveling at 2/3 the speed of light,
why can't you understand "slow wave coils"?
--
73, Cecil http://www.qsl.net/w5dxp