Hi Rick,
Well I have measured 2 of my 2 W/L Bevs. One of these has always been
at about 3m height, and away from any other conductors, and the IL is 4
dB. The other is a 2-wire one which started off at 1.2m height, and abt
300 mm above a fence. Last week, I measured its common mode IL at 7.8
dB (Differential mode was only 1.3 dB). Yesterday I raised its height
to 2.4m and the loss dropped to 4 dB. All I was really asking in my
original post, was to confirm that the reduction in IL is die to the
increased height and not due to the increased spacing above the fence.
I also measured the coupling from a 100m section of the fence before and
after. I simply used the same signal source as for the IL measurements,
but connected it to the top strand of the fence. In the original
position I found the coupling only 20 dB down from the direct connection
case, but after raising the height, the coupling dropped another 8 dB.
I have not been able to repeat F/B tests yet (I need a helper for this),
but certainly judging by the digi signal on 1818.5, I have improved the
F/B fairly significantly.
73, Greg, ZL3IX
Richard (Rick) Karlquist wrote:
> The problem with this concept is that first you have
> to know your ground parameters. What the NEC4 writers
> suggest you do to find ground parameters is to first
> run a wire(s) over ground and make physical measurements
> of it to characterize the ground. Then you fit the
> model to what you measured. Sometimes, it is impossible
> to make the model fit.
>
> I think you can now see that there is circular reasoning
> going on here, and you might as well just build the antenna
> and measure it and be done with it. You could possibly
> build a short beverage and measure that, and predict what
> would happen with 2 W/L. I know over my high conductivity
> ground, there is virtually no signal left after 2 W/L.
> I could predict this by measuring just 200 feet of wire.
>
>
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160 meters is a serious band, it should be treated with respect. - TF4M
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