"Walter Maxwell" wrote in message
...
On Sat, 12 Aug 2006 18:53:06 GMT, Cecil Moore wrote:

Walter Maxwell wrote:
But Cecil, I thought this thread was about chokes to prevent common-mode
currents from flowing on the feed line.

Now yer talking about loading coils for mobile whip antennas.

Yes, carrying the subject over from an earlier thread on loading
coils. There is a master's thesis paper authored by the Corum
brothers, K1AON and KB1EUD, and sponsored by the IEEE at:

http://www.ttr.com/TELSIKS2001-MASTER-1.pdf

which deals with RF coils. Although aimed at Tesla coils, it
contains lots of useful information for hams. In particular,
it predicts the VF for large real-world coils which is very
useful for me. It essentially shoots down the argument that
the current through a real-world loading coil is the same
at both ends of the coil, i.e. the delay through the coil
approaches zero as presented by the lumped circuit model.

As I understand
the issue, one is 180° from the other. For the choke you want a high
resistance,
which is what you get at the self-resonant frequency. But for the
loading coil
you want the lowest series resistance possible, which you don't get when
anywhere near the self-resonant frequency.

My point is that the same laws of physics apply to loading coils
and coaxial coil chokes even if the applications are different.
And we do, quite often, operate our 75m loading coils fairly
near their self-resonant frequencies - like your Hustler example.

Like I said above, the Hustler 80m loading coil achieved 'low swr' by
making the
coil self resonant slightly above 4 MHz, with a series resistance of 31
ohms.
Now you are suggesting a bugcatcher coil self-resonant at 6.6 MHz, which
means
yer coil is going to give you a nice low swr, but yer losing half of yer
power
in the coil because of the high series resistance you can't avoid. Yer
also
losing yer mind.

Well, that is the measured self-resonant frequency of my often
glorified 75m Texas Bugcatcher coil supposed to be one of the
highest-Q coils available.

Yeah, but Cecil, have you ever actually MEASURED the series resistance?
The
slope of the resonance curve that peaks at 6.6MHz ain't gonna be low
enough at
4.0. MHz to make an efficient mobile antenna. The Hustler coils, with 31
ohms
series resistance was a hoax on the average ham who didn't know the real
reason
the Hustler gave them a low swr, which is what they mistakenly thought was
paradise. When it comes to efficiency in an antenna with a loading coil,
the
best efficiency comes with the highest swr in absence of any attempt to
match
the terminal impedance to 50 ohms.

IMO, Cecil, you've been hoaxed if you thought a coil self-resonant at 6.6
MHz
was a high-Q coil at 4 MHz.

Walt

If the Hustler isn't bad enough you can always get a hamstick.

73
H.
NQ5H

"Reg Edwards" wrote in message
...

"Cecil Moore" wrote
So what would you call the frequency at which a coil alone
is resonant when mounted as a base-loading coil over a
ground plane?
=================================
Cec,

I would call it the frequency at which the coil alone is resonant when
mounted as a base-loading coil over a ground plane.

It would depend on whether the ground plane was a bicycle or the deck
of a super-tanker.
-----
Reg.



Wouldn't that just be a coiled-up whip?

H.