I think sometimes we go "overboard" with this interaction issue.
Using any modeling program, start with a dipole and then introduce
another wire and TRY to make a pattern.
Only when the second wire is close to resonance, and at the right
spacing are the currents correct to develop a pattern. This new wire
needs to be accurate within inches in length to make a pattern. After
all, this is why it can be so difficult and time consuming to adjust a
Yagi model (or in the real world on a tower) for optimum F/B. That
reflector (or director) has to be "just right" or it won't do a thing.
Modeling and experience shows that introducing
another...non-resonant...element will tend to load the existing wires
and hence lower the resonance point. The models show that some current
does flow in the added wire, but it's effect on the pattern ****at the
new resonance point****is negligible unless it is tuned "just right".
The important point here when modeling the interaction is to model the
new system at the ***lowered resonance point***, otherwise, the
conclusion would be that the pattern has changed. The system just needs
to be re-tuned.
As far as the steel roof.....good luck modeling that with confidence.
What conclusions or adjustments would be made armed with such a model ??
My recommendation to Con was to retune the thing and ***field test it***
for best F/B.
de steve ve6wz.
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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