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Re: [TowerTalk] half square ground screens

To: <>
Subject: Re: [TowerTalk] half square ground screens
From: "David Thompson" <>
Reply-to: David Thompson <>
Date: Fri, 12 Aug 2005 14:49:07 -0400
List-post: <>
A half square is the Bob-Tail as W6BCX envisioned it.  The common bob-tail
with three vertical wires is
a double bob-tail or three element bob-tail.  Somehow this gets lost in both
the W6SAI and ARRL Handbooks.

There are two ways to feed the bob-tail or half square.
At the top or at the bottom.  Feeding it at the bottom
requires a matching network and radials.  You can elevate it and still feed
it at the bottom with the matching network.  You still need radials and
either a ground screen or perhaps using Christman's gull wing radials might

The normal half square that is written about is fed at the top of either
vertical leg making sure the coax comes away at at right angles to the leg.
Get the vertical legs up at least 1/8 wave to minimize ground losses.  A
ground screen or radial systems probably won't help (see W4RNL's notes) but
may make you feel better.

Another version of the bob-tail is the robert-tail which is an upside down
bob-tail with the horizontal either lying on the ground or elevated
slightly.  A SK W8 used this effectively but never saw any test data or even
empirical results.

Ground screens do work.  I have seen rolls of chicken coop wire rolled out
in a crossing pattern.  There was an article in a late 1970's Ham Radio
Magazine by a WB0 which is quoted most often.  (see ARRL Antenna Book or
ON4UN's notes).

Sorry I cannot be more specific but an away from my source materials.

Dave K4JRB


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