To: <towertalk@contesting.com>
> Date: Fri, 12 Jun 1998 11:44:51 -0400
Hi Guy,
I'm not knocking no-radial antennas. Many people have limited room or
don't want to go through the work to use radials. They don't mind
five dB here and there of loss, as long as someone hears them. I
don't think that way and even enjoy messing with wires, so my
preference is a tad different.
No-radial or small-radial antennas are very worthwhile at solving
problems of space and ease of installation, even though they
provide those advantages with a definite reduction in performance.
Nearly everything in life is a compromise, this area is no exception!
> Even though its center-fed and detunes terribly if you add stuff to the
> shield of the feed coax (currently has a current choke on it),
> If I put down sixty or so 40 meter radials on the ground underneath, you
> would estimate the kind of improvement 4 maybe more db?
I'd bet the ranch, and win, the system would gain field strength. How
much is another issue. I'd make no bets on the amount because I
have no direct experience in that exact situation, and I don't trust
models of fields near unpredictable earth and clutter.
I'd GUESS more than a few dB, depending on soil IF you kept
the impedance matched.
> The Titan really is a center-fed vertical dipole - just with bunch of
> tuning stuff hanging off it. The wire at the bottom is not a
> counter-poise. It's two different "bottom hats" ... short for 20 m,
> longer for 40 meters, and not involved with 30 or 15 & above.
A dipole is 1/2 wl long end to end. A "loaded dipole" is a better
description.
For a given length radiator like this, true radiation resistance (as
opposed to meaningless feedpoint resistance) increases when the
antenna is fed as a marconi against a good ground system. Efficiency
goes up, assuming all other losses remain equal.
That's why if I was going to add a ground, I'd just base feed the
antenna.
Field losses would decrease also, since claims a small fractional
wavelength spacing or less is distance enough to isolate antenna
fields from lossy earth are simply not true. That's the case no
matter what kind of radiator is involved (even a loop).
Finally, I'd install hi-Q traps and lose any lossy coax loading
system. Claims are often made stubs offer lossless loading, that
isn't the case. Especially when the stub is a hunk of small coax
operating at an astronomical SWR!
Almost any all band system can be improved, the question is always
time, money, and return on investment.
73, Tom W8JI
w8ji.tom@MCIONE.com
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