[Antennaware] Modeling

Joe Giacobello k2xx at swva.net
Mon Mar 8 10:59:53 PST 2010

I understand the reservations regarding modeling ground mounted 
verticals.  However, I've had very satisfying results in modeling 
quads.  In one case I modeled and built a six band quad with four 
elements on 10-20M and seven on 6M.  I had similar results with a two 
element quad for 30 and 40M.  My criterion for success was that each 
antenna required little or no pruning to get the resonant frequencies 
somewhere within the bands, if not subbands, of interest. I did not even 
attempt to verify gain or F/B. I had equally good results when modeling 
a 40M vertical with four elevated radials, which was obviously not a 
very demanding task.  That six band quad had something approaching 1200 
feet of wire in it.

When Rudy, N6LF, published his experimental data for radial number, 
length, etc. for 40 and 160M ground mounted verticals on his website, I 
tried to develop a correction factor that might allow EZnec to conform 
to his data, but I could come up with no useful pattern.  It just didn't 
make sense and I threw in the towel.

When I modeled my own dual band, ground mounted vertical for 80 and 
160M, I used some of the tips that K2AV had suggested in various posts.  
If I recollect correctly, the model got the reactance close to right but 
the radiation resistance was off (high) by about 50%.  Nevertheless, the 
model was useful for providing direction on the effect of top hat 
radials, perimeter wires, etc.  The resonant frequency of the unmatched 
vertical was 2.3 MHz and the model predicted 2.15.

I'm no expert in either antennas or modeling, but those are some of my 
experiences.  Given the relative ease and reliability of modeling these 
days, I wouldn't consider building antenna without first modeling it.

73, Joe

K9AY wrote:
>>> Modeling of antennas? Design, build, it works as modeled.
>>> WX7G
>> I have all the scars and memories of wasted time that would prove
>> otherwise.
>> K2AV
> When the finished product works exactly as modeled, it is ALWAYS a 
> combination of:
> a) The model's ability to represent reality.
> b) Consistent, predictable behavior of the construction medium.
> c) The designer's ability to know when his/her design satisfies (a) and (b), 
> so he/she can stop tweaking the model and get it built.
> This applies to antennas, hypersonic aircraft, or the latest 
> multi-band/multi-mode SDR transceiver chip for your smartphone. As Dave 
> notes, many things are accurately built based on modeling. But as Guy says, 
> there are also many cases where (a) or (b) is insufficient.
> 73, Gary
> K9AY
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