NEC-LIST: Quad Modelling

Hi all,

I haven't done a lot of modelling with NEC so these questions might
seem a bit naive. I'm trying to model a quad from an ancient magazine
article, using NEC4WIN95 (MININEC).

It's a dual-band quad, 4el on 144MHz, 3el on 50MHz. But for now I'm
starting simple and want to model just the driven element for 50MHz.

Initially I set it up as five wires, with a break in one side where
the feed attaches. But that's not really a good model, because it's
meant to be used with a balun (and I don't know how to tell NEC that
there are two feed points that are a single balanced feed). And
NEC4WIN95 won't let me put the feed right on the end of these
segments.

So then I used 4 wires and just put the source in the middle of one.
But the SWR figures from both configurations are just awful; the
lowest SWR is at 55.5 MHz, and it's only 2.5:1; it should be much
lower, and around 50 MHz. It's a quarter wavelength per side.

So, what stupid mistakes am I making? Must be some good ones! The
director and reflectors are the same size but have tuning subs, which
should make the modelling even more interesting... I've included the
model below.

thanks
Hamish

(It's 4'10", or 58" per side. I put it 15" in on the x-axis because
the reflector will be at x=0.)

CM
CM NEC4WIN95 File
CM 2m and 6m quad from Feb 63 QST
CE
GND Reference
UNITS Inches
Height 236.220
Over Perfect Ground
Boundary Circular
F 50.000
GW 1 10 15.000 29.000 -29.000 15.000 29.000 29.000 0.080
GW 2 10 15.000 -29.000 -29.000 15.000 -29.000 29.000 0.080
GW 3 10 15.000 -29.000 29.000 15.000 29.000 29.000 0.080
GW 4 10 15.000 -29.000 -29.000 15.000 29.000 -29.000 0.080
S 1 35 100 0
Coax 50
Received on Fri Feb 25 2000 - 04:58:19 EST