Guy,
I'm looking at your antenna at W0UCe's website:
http://www.w0uce.net/K2AVantennas.html
Does the sections of the folded counterpoise have to be separated from each
other or can they be adjactent to each other. I'm thinking of constructing one
using zipcord for the FCP.
73,
Mike N2MS
----- Original Message -----
From: Guy Olinger K2AV <olinger@bellsouth.net>
To: Jim Miller Waco Texas WB5OXQ <wb5oxq_1@grandecom.net>
Cc: topband@contesting.com
Sent: Thu, 08 Dec 2011 01:57:20 -0000 (UTC)
Subject: Re: Topband: Best small space antennas
Note: the following is not a theoretical or untested antenna. There
are working antennas in the field using the folded counterpoise
described below, scoring well in contests**, in use up to a year and
more. Contest scores of the sort attained are not made using antennas
with significant deficiencies or fundamental flaws.
A miscellaneous end-fed inverted L or end-fed inverted U over an
elevated 5/16 wave single wire folded counterpoise (FCP) will have
good radiation from a small lot, with the ability to put out a strong
signal not usually associated with small lots. In the simple
implementation of this antenna (160 only), the length of the L or U is
adjusted for zero reactance, usually resulting in a 50-60 ohm feed Z
at resonance.
There are NO radials. The main design point of the antenna is to
minimize lossy currents induced in the dirt and confine TX signal
current to the FCP and the radiating wire. This is a real, and lossy
issue for a few short or miscellaneous radials. Enough of an issue to
kill 15 dB.
The radiating wire first goes up as much vertical as you can manage,
then out as far as manageable, and then down if length is still needed
to prune to resonance. The main point is to pick a feed point on the
property that has your best vertical rise and then get the rest of the
length for resonance however you can. For some properties this has
meant putting extra angles in the up+over+down radiator. Some
properties will not need the "down" part.
The antenna uses a REQUIRED isolation transformer at the feed point
because the counterpoise is NOT resonant, and the feed would really
rather use the much lower Z but hugely lossy coax shield current as a
counterpoise. The folds in the FCP are designed to maximally reduce
counterpoise fields at the ground, reducing lossy currents in the
dirt.
The isolation transformer's leftover inductive reactance, a
disadvantage in many applications, in this case helps to tune out the
capacitive reactance of the FCP and reduces the length of the
radiating wire needed to achieve simple resonance for the antenna.
The counterpoise extends plus and minus 33 feet from the feed point,
167 feet folded into 66 linear feet occupied on the property. The
middle 20 feet of the 66 should be straight, but either end can be
bent away from the straight line to accommodate the property. Up 8
feet or higher is recommended. Lowering the counterpoise increases
the coupling to dirt, increasing losses.
The isolation transformer uses the same physical components as a
balun, but the unlike the balun there is NO connection of any kind
between the primary and secondary windings. This is accomplished with
twenty bifilar turns of double polyimide insulated #14 with teflon
sleeving wound on an Amidon T300A-2 #2 material powdered iron toroid.
One wire is the primary, and the other is the secondary. The low MU
powdered iron toroid was picked over time to avoid heating, still
provide required coupling, with other choices sometimes failing in
spectacular fashion. We have no information of our currently-used
winding method on the Amidon T300A-2 ever failing for any cause,
though we would not expect it to survive a direct lightning strike.
With the isolation transformer, the antenna and FCP is entirely above
ground and not connected to anything else. We use a 5 megohm resistor,
in parallel with a non-resistor lawn mower spark plug, from the FCP to
ground as a static drain. The gap drains lightning induced voltage to
protect the resistor, the resistor drains wind, snow, rain static.
The resistor and gap protect the winding from a voltage puncture that
will grow into a carbon track to ground.
73, Guy.
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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