I’ve been scratching my head for years how to model an appropriate ground with my ground mounted Vertical Antenna radials.
I’d like to thank Sigi, DG9BFC for clearing this up for me.
HOW TO:
NOTE: I like to draw a small feedpoint in all my HF antenna models, like a 5cm length of wire where my “source” (coax) is connected to. Particularly useful for fan dipoles and for making other adjustments. I’ve left that part out for simplicity on this How To since I’m trying to make this super easy.
- Go to Edit > Wire Edit (CTRL-W) and click on the XZ (or YZ) button, bottom right of the Wire Edit screen.
- Click on the New Wire button and draw a line from Z=0 (the ground) straight up for 10m length.
- Click OK.
- Go to the Geometry tab and in Sources (bottom left), type W1B (Wire 1, Base).
- Click the View tab and ensure that the source is at the bottom of the antenna.
- Now head over to Calculate and type in the Freq box “7.2”.
- In the Ground section, click on “Real” and also click the “Ground setup” button.
- You may the leave the Dielec and Ground conductivity as the default. If you want some accuracy, check my link at bottom of this article. I am often near the sea at my holiday QTH so I adjust these up a little bit to 20 and 10 respectively. Pure salt water is much higher than that.
- Now add the number of radials you are planning. I normally use about 30.
- Click OK and you are now “Good to go”. Hit the Start button and you should see an impedance of around 35 ohms and SWR around 1.5:1. The antenna is actually fractionally short, so you may lengthen to suit.
That’s it! Years of work trying to figure this out and Sigi showed me today.
Of course, do NOT raise the antenna off the ground. The antenna needs to touch. So if you find something it wrong, you may find the antenna wire that you are feeding isn’t touching ground with Z=0.
Note: if your feedpoint ends up at the top of the wire and not the bottom, change W1B to W1E (Wire 1 Base -to- Wire 1 End). That’s it.
Ground Conductivity. A very heavy article can be found here: https://www.qrz.ru/schemes/contribute/arrl/chap3.pdf however for sake of simplicity, see the chart in the last picture in the gallery on this page.