To: <topband@contesting.com>
> Date: Fri, 06 Mar 1998 00:09:53 -0500 (EST)
> the clue, i.e., if there's no man-made noise in the area, the vertical
> doesn't have any noise pickup to re-radiate into the Beverage, therefore
> there might appear to be no effect -- except perhaps for the Beverage's
> directional pattern.
>
> 73, de Earl, K6SE
Hi Earl and others,
The real key is in the coupling between the systems. If the
conductors (antennas) have a high level of mutual coupling, they will
affect each other in some way. Resonance, or more properly even
being NEAR resonance, increases mutual coupling dramatically.
With that thought in mind, you can see why resonant radials,
with or without a resonant vertical, can affect anything else
near them. That includes the lossy earth near the radials,
telephone wires, rotor cables, feedlines, etc. etc.
In order to reduce that effect, you have to stop or reduce the
current flowing in the unneeded conductors. We do that in guy lines
by breaking them up into short lengths with insulators, and we can
also do it (less effectively) by simply detuning them.
There is one other way to stop this problem. Distance.
You can simply keep things far apart, so mutual coupling is low.
The important thing to remember is even if you don't notice an
observable "noise increase", a pass near another conductor
that is coupled to the receive antenna can still hurt S/N ratio by
changing the directional pattern of the receive antenna.
I have a Beverage that ends over 200 feet from the closest element
of my four square array. I can actually watch signals change level on
that Beverage while I switch the four square, and there is NO
problematic coupling between those antennas other than via the
"spatial" coupling between them. Even so, there is a degradation in
S/N ratio at times without a noise increase, because the desired
SIGNAL sometimes drops slightly when I fire the four square into the
Beverages direction!
ON4UN offered an excellent "rule of thumb". The best way to insure
you won't have a problem is to not set yourself up for trouble (if
you can avoid it). Why depend on luck unless we have to?
It proves nothing when Mr. X does something less than ideal and
works 9 zillion countries......... he might be a lucky guy, have a
better location, or spend more time operating. The antenna is only
one item in a complex chain of events that leads to a large country
total.
73, Tom W8JI
w8ji.tom@MCIONE.com
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