NEC-LIST: More on the ground stake effect.

Good day,

Last month I reported that using an 8 ft. ground stake
improved the SWR and raised the radiation resistance of my
HF-band volume-loaded dipole. Since then, I have learned
the following:

1. Putting a coax choke balun near the antenna reduced the
SWR between 3 and 3.5 MHz. It was a little worse on 20 m.

2. On a ground-wave test the ungrounded antenna produced a
10 dB improvement over the grounded antenna. My transmitter
was matched to the coax in both cases. Balun still in.

3. I have a copy of NEC4 left over from when I worked for a
now-extinct company in 1987. The manual says I should be
able to model a vertical wire penetrating ground, as long as
I have a segment end at the boundary. It didn't work, I got
the same error message I get with NEC2.

4. I looked up the reference to ground-stake calculations
given in the manual (Burke and Miller, IEEE Trans. A&P,
October, 1984). Their example of a quarter-wave antenna
driven against a ground stake shows the same trends for
terminal tresistance and radiated power. That is, the
ground stake radiates a lot of the power into the ground,
and this shows up as an inc4rease in terminal resistance.

I conclude that having a ground stake might be a good idea
for lightning protection, but it should be rf-decoupled from
the antenna.

Doug Miron

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