My experiences using EZNEC have shown that a problem with modelling a
commercial antenna of this type is the need to use monotaper element electrical
equivalents for the tapered physical elements. Care must also be given to
that the segment lengths for the elements are as constant as possible.
I believe that the Leeson tapered element compensation is running under the
hood of EZNEC, and that it is only valid for elements that have a few percent
delta from resonance of the desired frequency. What this means is that a 10m
or 15m tapered element will not model properly when the desired frequency is
20m. To see the true effect of the elements of the "other" bands on the band
that you are running means you need to use the monotaper electrical equivalents
of those elements.
73 es GL,
Antennaware mailing list