Tuesday, March 31, 2009

160 m Windom antenna modeling

Recently W4BXI provided some details (left) of his 160 m Windom antenna, since I had offered to model it with the 4nec2 software.

The screen shot below is a representation of the antenna structure data as entered into the program. Click on any image for an expanded view.The white lines are the wire elements and the blue lines are the feedline. A level ground is used for convenience, but the actual antenna site has some sloping ground as noted in the details sent to me.

Below are some of the results. The main program window shows impedance, etc. at the end of the 450-ohm feedline. Impedance at the transmitter end of the feedline is calculated to be quite high: 3797 + j861 ohms. I intend to check this using alternate tools (e.g. Smith chart). I expect it to be very dependent on the length of the feedline.

A sweep of frequency from 1.6 to 2.0 MHz yields the following SWR and reflection coefficient curves. This is based on a 50-ohm source with no matching. Naturally, the SWR looks better when using a 72-ohm feeder.

The program provides a tool for calculating several types of matching networks for matching to the designated 50-ohm source. Here are the results.

Also available are several forms of far field pattern plots in horizontal and vertical planes. Here is the horizontal gain plot.

3D plots of gain in various forms are also available. Here is one example that uses color coding to represent intensity. The antenna structure is also shown in this plot.

Text output files are also available if you want to examine or separately plot all the results.

1 comment:

Roger said...

Thanks for posting. Have 26-' and 130' windom, wanted to see some models
73 Roger N3RC