Re: [amsat-bb] EZNEC model

[K5OE@xxxxxxx]

Bob,
There is no perfect solution when building grid simulations, but I have found using closer-spaced wires with fewer segments to be more realistic than using wide-spacing and many segments.  I generally aim for segment length and wire spacing to both be around 1/10 wl, so your original model idea is sound.  Reductions beyond that seem to have little impact.  Increases in spacing start giving false feedpoint impedance values--although the patterns seem virtually unaffected.  As I recall the oblique angle of the antennae on PCsat, in the middle of the edges, you would only need to model 2 sides of the cube unless you were modeling all the antennae as an array--a daunting task and perhaps beyond the capabilities of PC-based NEC software.

FWIW, NEC4Win95 has a "virtual wires" version that allows unlimited wires/segments using your hard drive rather than memory, but I have found it craps out at about 3500 segments (or else my 500 MHz computer just gives up).
73,
Jerry, K5OE

> EZNEC Experts:
> 
> I'm trying to model a 1/4 wave monopole on the corner of a 1.5 wave length
> cube.  But to get the wire grid down to less than 0.1 wavelength spacing,
> I run out of lines and/or segments.  Or end up with only one segment per
> line which I thought is bad.
> 
> In otherwords, what are the rules of thumb about making large groundplane
> surfaces...  Any advice is appreciated.  This is the GPS antenna on PCsat.
> 
> de WB4APR@amsat.org, Bob
> 
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