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.
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!