At the risk of "flogging this horse to death", but just to re-inforce
Jim's point:
> Again, EXACTLY RIGHT. The missing data for the model are those things
> you forget about when you build the antenna, or are too complex for
> the program to compute.
In developing my new Broadband Hexbeam I consistently saw a small, but
significant, frequency offset between what EZNEC predicted and what I
measured on the prototype antenna. I even had Email exchanges with Roy
Lewallen to see if he was aware of some problem with his software. He
simply encouraged me to make sure I had taken all factors into account
in the model.
Eventually I realised that I had failed to include in the model the
small connector blocks which I used to join the tips of the wire
elements to the insulated spacer cords. They were adding significant
"end capacity". Once I included them, the frequency error disappeared
and I got even better correlation between the F/B predictions and the
measured results.
Moral: you can't expect EZNEC to take into account the things you don't
tell it about :)
73,
Steve G3TXQ
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