Re: NEC-LIST: connecting wires to real ground in NEC2

>Hi,
>
>Can anyone help?
>
>I'm trying to model the current distribution over a horizontal wire
>above lossy ground. The horizontal wire needs to be terminated at
>either end by vertical risers connecting to lossy ground. Is it
>possible to model such a lossy transmission line in NEC2? Is one
>allowed to make a direct wire connection to lossy ground?
>
>Thanks
>Joe Trinkle

Joe,

I have simulated "ground connection" by using *resonant* quarter
wavelength radial wires, very-very close to ground (#12 wire 5 mm
above ground).

If you want to to simulate a good ground connection use many wires ---
say 30-60. If you want to simulate a mediocre connection (a stake
ground) use only a few wires --- 3 or 4. If you want azimuthal
symmetry you cannot use less than 3-radials.

If the horizontal portion of the antenna is too close to ground, then
it makes a difference when using few radials whether the elevated
hoirizontal wire is directly over a radial wire, or on bisector
between radial wires. "Over a radial wire" increases the current in
the radial wire beneath (transmission line effect) and increases the
effectiveness of the simulated connection to ground (e.g. for a T- or
inverted L-antenna).

For elevated GP type antennas the same proceedure can be used ---
resonant radials can be using to simulate performance of elevated GP
antennas --- and this technique certainly works. As few as one radial
can be used, if you want to have directivity --- maximum gain in
direction radial is pointing.

Jack

References:

Belrose, Communications Quarterly, Winter, Spring 1998 issues; and
Spring 1999 issue (on press).

_____________________________________________
John S. (Jack) Belrose, PhD Cantab, VE2CV
Senior Radioscientist
Radio Sciences Branch
Communications Research Centre
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>
_____________________________________________
Received on Tue Apr 20 1999 - 16:08:51 EDT