Ron and all:
You can use your tower as one leg of a folded monopole. Run a wire
vertical up one side of your tower separate say 6-12 inches from the
wire shorted over to the tower top. Tower stays grounded and your
wire it fed at the bottom near ground but insulated. Coax shield is
tied to tower ground. Depending on tower height you still may need a
tuner to match it. 80m works nice with 60-foot tower. You still
need ground radials like any 1/4 wave vertical. The tower makes a
nice fat element to lower Q.
If you have a mast with HF antennas at top there will be a little
capacitive loading to the resulting vertical.
73, Ed - KL7UW
Date: Wed, 1 Mar 2017 10:41:40 -0800
From: "Ron D'Eau Claire" <[email protected]>
To: "'Charlie T, K3ICH'" <[email protected]>,
<[email protected]>
Subject: Re: [Elecraft] 80 Meter Verticals
Message-ID: <003501d292bb$780e04d0$682a0e70$@biz>
Content-Type: text/plain; charset="utf-8"
John Heys, G3BDQ, in his book "Practical Wire Antennas" describes
"folded monopoles" or "folded Marconi" antennas - essentially 1/2 of
a folded dipole worked against a system of radials. The monopole is
made of two or three wires. Feed is between one wire and the radial
system while the second or third parallel wires are jointed at the
"top" and retur to be connected to the radial system.
A two-wire folded monopole presents a feedpoint impedance of between
80 and 150 ohms. Heys credits W6SAI in his book "Simple Low-Cost Wire
Antennas" (Radio Publications, Inc., 1972) for a version made from
slotted 300 ohm "twin lead". It is in Inverted L configuration for 80
meters: vertical 30 feet (9.1 meters) then sloping 25 feet (7.6
meters) to the top of a 35 ft (10.6 meter) support. To maintain
resonance and compensate for the velocity factor of the twin lead, an
8 ft 3" (2.4 meter) single wire is run from the joined conductors at
the end of the twin lead to the support.
Heys describes a 3-wire version without a bend but sloping at an
angle of 30 degrees or less from vertical at 65 feet (19.8 meters)
centered on 3.6 MHz. Heys' version requires a 60 foot (18.2 meter)
high support although he notes that for 40 meters a 30 foot support
will be adequate. As with the two wire folded monopole all three
wires are connected at the "top" and the feed point is between the
center wire and the radial system. The other two wire ends are
connected directly to the radial system. Heys notes that a spacing of
1 foot is needed to use the common 1/4 wavelength formula of 234/f (mHz).
Heys says that either antenna can be used on its 3rd harmonic.
73, Ron AC7AC
73, Ed - KL7UW
http://www.kl7uw.com
Dubus-NA Business mail:
[email protected]
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