Re: NEC-LIST: Example helix antennas for NEC2?

A number of folks were kind enough to respond, but alas, not much proved
to be very helpful. Not one person supplied a NEC2 deck. Three said i
suggested using their software (two commercial and one not), none of which
is very useful, especially given i'm neither running Windows nor using an
Intel-compatible processor. The non-commercial person also supplied a
source file, one of only two folks who did. A couple of people gave some
general guidelines, much of which i already knew.

The supplied file(s) were all in formats other than NEC2, and a third
person supplied a link to one (also in another format) which was the best
one i had found prior to my earlier posting. Alas, the one which did have
a plausible impedence didn't use a reflector (used a ground card instead??)
came out as 10dBi (where 18dBi was predicted by a formula found elsewhere),
both forward/reverse. In the other case (a pair of helix antenna, with
different reflector mesh intervals), was for NEC4. My attempts to convert
the version whose compute time seemed feasible for my computer yielded an
impedence of 154 +j281, whereas the author reported the pair as giving
195 -j138 or 185 +j30 (not completely clear which was which).

Attached is one of my own attempts, starting with ideas from AF9Y. It
also only gets about 10dBi (where 17dBi is predicted), but at least has
good impedence (approx. 50 ohms, j<8 for 1240-1300 MHz) and the pattern
looks plausible. But it does use a ring reflector, which may or may not
be as good as a simulated plate. It is constructed for 300 MHz (that is,
1 meter = 1 wavelength) and scaled to the target frequency. I'm not sure
i'm exciting it properly. Feedback/suggestions are welcome.

=> Again, can anyone supply a NEC2 deck which models a helix well for both
=> impedence and pattern?

Also, do you get similar results with the attached file? Or is perhaps my
copy of NEC2 (or NEC2 in general) broken in some way? Or does NEC2 not do
well at modeling this type of antenna?

                                -- KD6PAG

-------------------------------------------------------------------------------
CM Experimental Helix
CM
CM Reflector radius: 0.183
CM Reflector element: 0.02
CM Feed element: 0.02
CM Feed length: -0.016
CM Helix element: 0.02
CM Segment 1 turns: 0.25
CM Segment 1 radius1: 0.159
CM Segment 1 radius2: 0.159
CM Segment 1 spacing: 0.125
CM Segment 2 turns: 5
CM Segment 2 radius1: 0.159
CM Segment 2 radius2: 0.159
CM Segment 2 spacing: 0.25
CM
CE
GA 1 16 0.183 0 360 0.02 0 0 0
GM 0 0 90 0 0 0 0 0 1
GW 2 2 0.183 0 0 0.159 0 -0.016 0.02
GH 3 3 0.125 0.03125 0.159 0.159 0.159 0.159 0.02
GM 0 0 0 0 0 0 0 -0.016 3
GH 4 60 0.25 1.25 0.159 0.159 0.159 0.159 0.02
GM 0 0 0 0 90 0 0 0.01525 4
GS 0 0 0.2364
GE
EX 0 2 2 0 1
FR 0 11 0 0 1200. 10
XQ
FR 0 6 0 0 1260. 2
XQ
FR 0 1 0 0 1269 0
RP 0 1 73 111 90 0 90 5
RP 0 73 1 111 90 0 -5 90
EN
===============================================================================

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