Re: NEC-LIST: NEC2 versus NEC4WIN models

Hamish,

I do not know what differences you have observed, and, I know nothing
about NEC4WIN95. This may be a good program, but I consider that it
has a misleading name --- since NEC4 could lead one to believe that it
was a NEC4 program, rather than "NEC for WINOWS 95". I use EZNEC PRO.

Whatever quads are tricky to model. I have modelled quad elements in
two ways (in the past):

1) Choose a lot of segments; and

2) Employ fewer segments but use a segment taper option, tapering to a
segment length a few thousandths of a wavelength long at at all
corners. It is the corners that are tricky, sensitive to segment
sizing.

I suppose the modelling programs you are using are MININEC (the one
with an even number of segments); and NEC2 (the one with the odd
number of segments).

For your comparison I have modelled your quad beam with the best
precision I can: NEC4 (double precision), and conservatively
segmenting the wires at a frequency ten times the operating frequency.
This model has 50 segments/wire on the director; 53 on the driven
element; and 55 on the reflector element.

I calculate: resonant frequency 50.5 MHz; impedance 48.2 ohms; Gain
(free space) 8.18 dBi; F/B 24 dB. It looks like a pretty good
antenna.

73, Jack, VE2VC

_____________________________________________
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 Wed Mar 01 2000 - 06:18:00 EST