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 -----Original Message----- From: Elecraft [mailto:[email protected]] On Behalf Of Charlie T, K3ICH Sent: Wednesday, March 1, 2017 5:25 AM To: [email protected] Subject: Re: [Elecraft] 80 Meter Verticals Is there any truth in the theory of making the vertical radiator out of multiple wires such as ladder line and even adding a third wire woven through the ladder sections and fed on one wire? The physical result is three parallel wires but electrically connected so as to form and "up, down and up again" element. This supposedly raises the radiating element impedance relative to the fixed ground loss resistance. The idea I'm told, is that since the ground resistance (loss) is fixed at whatever it is but as the actual radiating element impedance is raised, the antenna becomes more efficient since the ground loss percentage of the overall feed point impedance is lowered. This impedance change happens in much the same way as a folded dipole feed is a higher impedance than a conventional dipole using a single wires. I saw this written up a few years ago as a means of increasing the overall efficiency of an inverted L for either 160 of 80 M. I had an "L" made of the smaller ladder line on 160 with only four ¼λ radials on the ground that seemed to work fairly well. My plan was to install elevated radials, but that would have been a LOT of wire around the yard. Something broke on it after a year or so, and I never re-installed it. 73, Charlie k3ICH ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
