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 [1].  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 model

The antenna was modeled using 4nec2, a free version of nec [2].  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      ross_anderson@comcast.net     January 8, 2008

Notes, References, and Links

[1] http://home.comcast.net/~ross_anderson/Pyramid.htm

[2] http://home.ict.nl/~arivoors/

 

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

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.

CM 

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.

CM

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

GE       1

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

EN