Wednesday, December 31, 2014

End Fed Zep Antenna by N4NR

After some recent morning QSOs on 3740 kHz, there was email discussion about the antenna used by N4NR from his campground location in coastal Georgia. Several of our morning regulars were impressed by the 10 W SSB signal from Dennis. The antenna is an End Fed Zep. (This is a correction to my earlier posting.)

Based on an email response from Dennis, I put together a model of his campground antenna. For my initial analysis I did not include his RV, but a later analysis could add a metallic screen near the vertical portion of the antenna to approximate its effects. I expect that this would show up mainly on the higher bands where the radiation angles are lower.

Below is a series of screen captures from the 4nec2 antenna modeling software to illustrate the theoretical behavior of the antenna. Click on any graphic for a larger view.

First is a view of the antenna structure. 17 ft of 450-ohm ladder line starts at the rig (tuner), goes about 2 ft horizontally, then 15 ft up a fiberglass pole. A single wire, connected to one side of the ladder line, continues up to 22 ft, then continues on an upward angle to a height of about 50 ft for a total length of 84 ft. The other side of the ladder line constitutes the counterpoise. The graphic is to scale, so the two conductors of the ladder line are hard to distinguish. On this version I also used the program's feature to depict the magnitudes of current in the structure, represented by the short green lines. 
The ground parameters are for "marshy, forested flat ground", and the wires are all 12-gauge copper.
Antenna Structure

Next is a series of 12 screen shots showing radiation patterns for four selected frequencies.  I included patterns for total gain, vertically polarized and horizontally polarized. All patterns are oriented in the same direction as the structure graphic above (x-axis and horizontal wires going to the right). The total and vertical patterns are from a low angle facing the antenna broadside, and the horizontal patterns are from directly above the antenna. Click on the slide show below for a better view of the individual slides.

Below you can view impedance plots for two frequency ranges: 3 to 14 MHz and 3 to 29 MHz. Click on any image for a larger view.

Impedance Parameters, 3-14 MHz

Impedance Parameters, 3-29 MHz

Happy New Year!