Re: NEC-LIST: NEC4D and buried antennas

Grant:

I modeled a center-fed insulated dipole buried 1 foot in dry sand,
computed the input impedance vs frequency and the vertical E field
launched off the end versus distance for several frequencies, and I
got excellent agreement. My tests were at HF, and I used the SRI
International Open-Wire Line (OWL) ground constants kit to measure the
conductivity and relative permittivity of the sand at each measurement
frequency. With those measured ground constants as input data, NEC-3I
predictions agreed very well with the measured data. There was a
better fit on the E field vs distance data (out to about 500 m asI
recall) than to the input impedance. By varying the frequency of the
predictions slightly, I could get excellent agreement for the
impedance as well.

I know that Gerry Burke put NEC-3I (the I for insulated wire) into
NEC-4, but I have no experience with NEC-4D. I do have faith in the
NEC-3I for the case you ask about--if you feed the model accurate data
for sigma and epsilon r (i.e., measured at the site of interest). I
assume that the basic algorithm was not changed in going from NEC-3I
to NEC-4/NEC-4D. Gerry could answer that for you.

The results were never published, but I believe I told Gerry at the
time that the code worked well. I had earlier done a small NEC-3
validation task for Jim Breakall when he was still at LLNL, and have
had an interest in the use of measurements for code validation for
many years, especially useful after the code vs code evaluations have
checked out ok. My NEC-3 validation work is in the Proceedings of the
4th ACES. I may get around to putting something into the ACES
Newsletter or Journal on this buried dipole work sometime. The work
was done in 1989, so the hardest part is finding the data!

I see no difference between buried transmitting and buried receiving
antennas from this standpoint. Do you expect a difference? If you pump
enough power into the buried antenna, then you might have to be
concerned about RADHAZ right over the antenna, but I didnt use high
power for my simple test.

I hope this input is helpful to you.

George H. Hagn

Grant Bingeman wrote:

> Has anybody used NEC4D to model buried transmitting and receiving
> antennas? Has there been any validation?
>
> Grant Bingeman
Received on Wed Jun 17 1998 - 10:41:12 EDT