Re: 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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>http://www.gweep.ca/mailman/listinfo.cgi/nec-list

You cannot let a wire touch ground using NEC-2, but you can simulate
ground connection by using many (16-32) resonant radial wires a wire
diameter or two above real ground.

I do not have measured data to validate NEC-4D's ground stake
calculation, but as far as I am concerned NEC-4D calculates
resistance values that seem to me to be very reasonable.

There must be something wrong with your calculating engine. The
program should tell you, at least EZNEC pro NEC-4D does, that the
calculation is invalid if you let a wire touch ground using NEC-2.

One has to be careful if the ground system is a buried radial wire
ground system, a single wire connecting to many wires, but a ground
stake is a simple model.

73, John S. (Jack) Belrose, VE2CV

-- 
_____________________________________________
John S. (Jack) Belrose, PhD Cantab, VE2CV
LIFE SENIOR MEMBER of the IEEE
Fellow Radio Club of America
Atyhlobne Fellow
Radioscientist Emeritus Researcher
Communications Research Centre Canada
PO Box 11490 Stn. H
OTTAWA   ON   K2H 8S2
CANADA
TEL  613-998-2779
FAX  613-998-4077
e-mail  <john.belrose_at_crc.ca>
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