Laszlo Szegedy wrote:
>
>
> 3.I have limited space for radial,no space for 1/4 wave radial ,I have only
> 15m(45 foot) for each direction?
> Anybody tried to use trap radial? To use a coil or capacitor in each
> radial? Or not?
>
>
> Thanks :Laszlo
>
>
> ____________________________________________
>
Don't bother with traps or coils in radials. What counts is the number
or radials even if they are short as I understand the greatest loss is
the current distribution closest to the actual antenna.
In the 45 foot area you have available place as many radials as
possible. You can even bend the ends at right angles so they approach
1/8 wave on 160. They need not be 1/4 wave and the result of many, 50
or more, will significantly reduce the ground losses at the base of the
antenna. Even consider a ground screen made from expanded cooper mesh
or even rabbit wire or chicken wire will work but since they are steel
the connection and longevity mayl be problematic.Only complex modeling
programs will give you the true picture. But a ground screen is worth
consideration as an alternative in my opinion.
In the 60's while working in the sales division of a major broadcast
transmitter manufacturer I was intrigue by observing the engineers on
the antenna test range removing 120 1/4 wave radials laid over a 50 by
50 foot ground screen. They watched and recorded the results on a field
strength meter at one mile. When they removed the last radial the
signal reduction was only 15%. This experiment was conducted over very
good Midwest soil. I suspect the results would have been much different
over poorer soil and at a greater distance.
There is one flaw in this test as the test was not run without a screen
since this had been buried first as a standard practice. However, it
made me a believer that a ground screen is a good idea when other
options are not available.
Herb Schoenbohm, KV4FZ
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