Tonight I will be the presenter of the program at the Tacoma Radio
Club. My topic will be antenna modeling (using EZNEC). I intend to
include the results of a discovery that I made a couple days ago and
will appreciate comments from this group if I may have made an "errant"
I modeled an 80m 2 element wire yagi. I chose wire lengths and spacing
to emphasize how the gain pattern can undergo a 180 degree reversal when
the frequency is changed from one end of the band to the other end.
My discovery was that the length of the driven element has little to do
with the gain pattern. Even shortening the driven down to 20 feet or
lengthening it to 100 feet made little difference in the gain pattern.
After thinking about it, it seems quite reasonable to me that the driven
element is primarily just a source for the frequency and phase
relationship to the parasitic element to determine the pattern
(except that the driven element length provides a multiple location
source but that has much less
influence on the pattern).
This "discovery" is probably common knowledge to many Towertalkians, but
I would appreciate comments, especially If I misunderstand what EZNEC
has shown, before tonight's presentation.
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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