Going back to the question of what antennas we use and why the work (or
don't), which continues to be a hot topic here, I have ordered a copy of Les
Moxon G6XN's book _HF Antennas for All Locations_ (RSGB via ARRL), which was
highly recommended to me. Along the way, I found an interesting article on
the ARRL website that some of you may find interesting:
The basic point is that we can get a
new look at verticals if we think of them as asymmetric dipoles. Verne
W6MMA's products are "wicked nice" engineering but they do not seem to be
plug-n-play (which is fine, we're experimenters?) -- so I am going to
continue to read and experiment and hope we can share feedback about what
works. The little FT-817 really does seem to encourage us to figure out how
to make more compact ants work well.
73
John Newell
KB1FPM
John --
The discussion...raises questions what
an antenna like the MP-1 (or the AP-10) with the appropriate
"counterpoise" <slap me! :-)> really is, and which part of
it is really doing the radiating (if the "counterpoise" is
the correct length)???
The $64,000 Question?
The article doesn't put it quite this way, but here's the gist, I
think:
Clearly the counterpoise radiates, unless you've gone out of your way
to waste the radiation, which is the point that Bonnie KQ6XA has been
making repeatedly.
But unlike an orthodox dipole, a lot of that radiation is involved in
heavy interaction with the "radiator" radiation, with phase
reinforcement or cancellation, secondary effects of ground reflection
and coupling, and so on.
One possible outcome is a very eccentric radiation pattern. But it may
be possible to smooth that out by redistributing and spreading out the
interaction through multiple radials or counterpoises, capacitance
hats, and so on. In the limit, this is a disk, of course; but still a
radiator, although with the "flattest" interactions with the vertical
element. Thus the classic advice to use as many radials (the best
approximation to a disk) as your patience will allow.
So an MP-1 with a proper single-wire elevated counterpoise is just a
half-loaded dipole with a radiation pattern to make your hair stand on
end. An MP-1 *without* a proper elevated counterpoise is just a waste
of watts. :-)
That's how I read it, anyway.
Frank
AB2KT
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