Wire Antenna for 75 and 80 Meters
This article is about a wire antenna that covers the entire 3.5 to 4.0 MHz band with an SWR below 2:1. It is a two wire log-cell of the Pyramidal Antenna, a log periodic antenna discussed in the accompanying article . The antenna consists of two coupled dipoles, one resonant at about 3.5 MHz and one resonant at about 4 MHz, resulting in the low SWR.
The antenna was modeled using 4nec2, a free version of nec . The antenna dimensions were determined by 4nec2’s genetic evolver with the following conditions: wire #14 copper, frequency sweep 3.5 to 4 step 0.1, segmentation 40 per half wavelength, impedance 50 ohms, SWR 100. The antenna was assumed to be 40 feet above average ground. The schematic diagram of the antenna and its SWR are below and also the 4nec2 program that created the data.
Ross Anderson W1HBQ email@example.com January 8, 2008
My homepage “Ross’s Antennas”, with links to my other pages, is http://home.comcast.net/~ross_anderson
Schematic diagram of antenna
The top wire is 677.5 inches long on the left and 789 inches on the right. The bottom wire is 789 inches on the left and 677.5 inches on the right. The spacing between the wires is 71 inches. The connecting wire is also 71 inches. The antenna is fed in the center of the connecting wire (marked by a circle).
Orientation of antenna over ground
SWR verses frequency
CM Wire Antenna for 75 and 80 Meters by W1HBQ
CM This program is written in 4nec2.
CM The dimensions of this antenna were determined using 4nec2
CM genetic evolver with SWR 100, characteristic impedance 50 ohms,
CM 3.5 to 4 step 0.1, auto segmentation 40 per half wave.
SY spx = 70.7977 'Spacing between wires.
SY sx = spx/2
SY hwl = 1578.328
SY ly = hwl/2 'Length of longer half element.
SY hws = 1355.018
SY sy = hws/2 'Length of shorter half element.
SY hz = 480 'Height of antenna over ground.
SY wrad = .032 'Radius of #14 wire.
GW 1 1 sx 0 hz -sx 0 hz wrad
GW 2 1 sx 0 hz sx sy hz wrad
GW 3 1 -sx 0 hz -sx -sy hz wrad
GW 4 1 sx 0 hz sx -sy hz wrad
GW 5 1 sx -sy hz sx -ly hz wrad
GW 6 1 -sx 0 hz -sx sy hz wrad
GW 7 1 -sx sy hz -sx ly hz wrad
GS 0 0 0.0254
LD 5 0 0 0 58000000 'Copper wire.
GN 2 0 0 0 13 0.005 'Average ground.
EX 0 1 1 0 1 0
FR 0 0 0 0 3.75 0