----- Original Message -----
From: "Charles Moizeau" <w2sh@msn.com>
To: "Topband" <topband@contesting.com>
Sent: Sunday, September 11, 2011 2:46 PM
Subject: Re: Topband: Fence "ground screen" instead of wire radials?
>
> My comment on this subject is directed to KM1H who in a recent posting
> said:
> > > I used 4' x 50' rabbit mesh (2x4") that was welded, then galvanized
> > > and then
>> > plastic dipped for over 10 years at a prior QTH. It was purchased that
>> > way
>> > at a garden store.
>> >
>> > Galvanizing is very easy to solder to with just normal rosin solder and
>> > all
>> > I did was run some stranded #12 copper to the #6 copper ring at the
>> > base of
>> > the shunt fed tower. A bit of spray autobody undercoating sealed the
>> > mesh
>> > solder connections.
>> >
>> > Prior to this there were 60 radials, 60-135' long and performance was
>> > fair.
>> > With the 4 sections of mesh on top of them it became a pileup buster
>> > and
>> > contest winner.
>> >
>> > Carl
>> > KM1H
>> > *********************************************************************
>> > Carl, I have great respect for much of the anecdotal material presented
>> > in this forum. I do find it quite extraordinary that within the first
>> > 50 feet of radius of your larger plot of 60 radials that extended
>> > variously to lengths
> of 60-135 feet, you were able to achieve a significant performance
> increase by adding four 50-foot lengths of four-foot wide rabbit screening
> (2" x 4"). What I see is that you achieved this by adding just 800
> square feet of screen to a an inner circle with a radius of 50 feet, whose
> area is approximately 7,800 square feet. Your "return" from 800 square
> feet of screen on an earlier "investment' of radial-laden 7,800 square
> feet is remarkable. I am guessing that your antenna was one whose current
> maximum appeared at its base, whereas mine, whose inverted L has its
> current maximum half way up its 85-foot vertical portion, would not
> achieve such spectacular results with the addition of the same 800 square
> feet of screen at the antenna base. My reasoning is that the radiation
> that my antenna bounces off the ground hits the ground at a point farther
> out from the base. Perhaps longer runs of screen would be helpful, or
> maybe the 50-foot screen lengths might better be planted at a
> distance of 50 or so feet AWAY from the antenna base. 73, Charles, W2SH
It doesnt matter what the radiator length is, the maximum FEED current is at
the base if its a base fed antenna.
Sevick showed decades ago that a very dense field of short radials is
superior to less than optimum long ones.
There was nothing spectacular about why the ground screen worked and the
radials may have covered 7800 square feet but they were only affecting the
ground where they were placed.
That shunt fed vertical with a Christmas Tree of 4 el yagis was self
resonant around 1570KHz if I remember.
Your antenna bounces nothing off the ground until it is many wavelengths
away. Its referred to as the Brewster Angle.
Carl
KM1H
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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