As a notebook exercise, I modeled some long Yagis that I have accumulated
(45' to 53' booms) for comparison--and came up with some interesting
features as well as some cautions about too hastily comparing models. All
done in EZNEC (NEC-4). Thought the exercise might have some small
interest, so I put the results at the site, in the Modeling part of the
index to the notes under the title of "Modeling 5 Long Boom 20-Meter
Yagis." All it proves is that you cannot simply slap two models
side-by-side and think that's the end of the modeling story (let along the
building and performance stories). The model descriptions are attached
to the notes for reference. Modeling multi-element beams is not the bear
some folks think it to be. For most that use the same taper schedule for
all elements, simply block copy the reflector and then adjust the spacing
column and the tip end values. This applies either to EZNEC or to NECWin
(where you can use the edit feature to copy and paste). But beware of
designs like the W3LPL Yagi that changes the tapering schedule at several
points.
Hope the notes are useful to someone.
-73-
LB, W4RNL
L. B. Cebik, W4RNL /\ /\ * / / / (Off)(423) 974-7215
1434 High Mesa Drive / \/ \/\ ----/\--- (Hm) (423) 938-6335
Knoxville, Tennessee /\ \ \ \ / / || / (FAX)(423) 974-3509
37938-4443 USA / \ \ \ \ || cebik@utk.edu
URL: http://web.utk.edu/~cebik/radio.html
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