Topband: Asymmetric radials for GP antennas; Just in case others seek what I've just found...
zr at jeremy.mv.com
Tue May 17 08:17:00 PDT 2011
Before I knew better, 30+ years ago, I had a 90' tower with 10-20 yagis
shunt fed on 160. It was about 40' from the road on the NE thru SW side so
many radials were very short and others ranged up to 120' long. The ground
was poor, consisting of deep sand with just a thin layer of topsoil.
It worked fair but not well considering I was running 1200W. Most DX
contacts required waiting in a long line.
Then I realized about current being maximum starting from the base and I got
a bright idea. At the local garden center I picked up 5 rolls of "rabbit
fence" which were 2 x 4" welded and galvanized wire mesh coated in green
plastic and were 50 x 4'. I laid these down in a spoke, stripped back some
plastic, and soldered the ends to the ground ring at the tower with #12
copper wire. I also connected them together at the far end of the overlaps
with another ring.
After retuning the match that antenna kicked butt.
After a bit of grass seed and fertilizer it was completely out of the way of
the lawn tractor in a few months.
----- Original Message -----
From: "Cormac Gebruers" <ei4hq.mail at gmail.com>
To: <topband at contesting.com>
Sent: Monday, May 16, 2011 1:20 PM
Subject: Topband: Asymmetric radials for GP antennas; Just in case others
seek what I've just found...
> I've been searching for clarity and hard data on the effects of asymmetric
> radials on radiation patterns and efficiency of a vertical as I'm
> a 21m vertical for 80/160 and will have to live with a radial system that
> significantly compromised over a 180 degree sector.
> I was a bit surprised to "not find" this subject dealt with in any clear
> decisive way in e.g. the ARRL Antenna Book or ON4UN's otherwise excellent
> Low Band DXing book (Did I miss it in either publication? If so, just send
> me a "your an idiot" email and I'll crawl back under my cabbage leaf
> suitably chastened).
> I was surprised as I had always assumed it is something many hams have to
> deal with unless they are prepared to go on "stealth missions" in the dead
> of night to lay radials on or under neighbours property (I don't recommend
> this course of action by the way; I attempted just such a thing once and
> caught. As a mental exercise to occupy you during those quite times when
> calling CQ on a dead 160m, try explaining your way out of that one).
> On the basis that there might be one/some/many out there, who, like
> are installing verticals with radial systems that are compromised
> directionally as well as "length-ways", I just thought I'd share what I
> found; N6LF's excellent (if not exactly encouraging) summary of the
> consequences of asymmetrical radials at
> http://rudys.typepad.com/files/qex-ground-systems-part-7.pdf . It's well
> worth the read.
> I hope to hear you all on the far side of the Summer...
> Cormac (EI4HQ)
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