> Elegant analysis, Tom. Thanks. I looked at Guy's very well done piece
> in the National Contest Journal (the one timed for reading on the
> airplane going to Dayton) and wondered why a serious common mode choke
> would not work.
Thanks, not really so elegant though.
Any common common mode choke will work, if the system were made resonant.
The problem is the counterpoise system appears to be pretty far removed from
resonance. If the system was resonant, the coupling system recommended would
actually not work at all. It would cause a terrible SWR.
> Guy's dimensions are quite specifically tailored to fitting in a small
> space, so it would be nice to keep it there. So The obvious next
> question is, is there any reason why Guy's 66 ft FCP could not tbe made
> to work by adding that inductor and a suitable choke? Or perhaps
> another fold?
I played with an increase in wire spacing, which improves things all the
way around. I am documenting it here:
http://www.w8ji.com/fcp_folded_counterpoise_system.htm
I'm still working at that off and on.
It's probably important to point out the general trend of folded wires,
which is also sometimes called "linear loading". The general trend is with
**tighter fold spacing**, loss increases, bandwidth decreases, and more
conductor length is required to maintain the same resonant frequency. Wider
spacing is virtually always better. Close spacing, once near very small
fractions of a wavelength, does not reduce radiation. As a matter of fact,
we don't want that anyway. If a counterpoise has no external fields, it
cannot be a counterpoise at all!! The only way to make an effective
counterpoise that virtually does not radiate is to make a very large
balanced counterpoise, and that still only cancels radiation in the far
field.
Simply increasing spacing from 0.4 feet to 1-foot moved the 36 foot "radius"
counterpoise down in frequency almost to 1900 kHz, from what initially was
well above 2 MHz.
There are about a dozen ways to skin this carcass, none of which are going
to be significantly different than any other **PROVIDED** the counterpoise
is properly resonant. There isn't any magical exceptional solution,
everything properly done is about the same for the same area.
It's a cruel world on low bands.
The real question is how to tune a counterpoise for true resonance. I can
think of only two ways to do it. Measure voltage at the common point to
earth and tune for minimum voltage to earth, or feed two counterpoises as a
dipole.
One thing for sure though, the system now is far from resonance. That is why
it takes a special coupling device.
73 Tom
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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