I sent this earlier but unfortunately only to Pete and not the group. Here
it is again.
At 04:47 1/31/01 -0500, Pete Smith wrote:
[my earlier comments snipped]
>Unfortunately, modeling linear-loaded antennas with NEC-2-based programs is
>an uncertain activity, at best. Even if you accurately represent the
>structure of a Force 12 "N" element in the program, my understanding is
>that closely-spaced adjacent conductors of differing diameter are very
>difficult or maybe impossible for it to model accurately.
Yes, the linear loading modeling is problematic. However, for this
experiment I believe that installing equivalent "loads" at the appropriate
points would be valid.
>
>Moreover, several technically well-versed people on the reflector have
>suggested that antennas in close proximity may exhibit interactions that
>are not directly related to the presence or absence of common resonances.
Maybe I'm not "technically well-versed" enough to comment, but I certainly
hope that these interactions do occur. Otherwise all of our parasitic
antennas won't work. After all, Yagis, at least the ones most usual, do
not have "common resonances." Each element is resonant on a different
frequency.
I'll bet that most of these people embrace computer-optimized Yagis, which
I believe includes any currently marketed. If they accept that the programs
accurately model closely spaced elements, resonant on different
frequencies, why can they not accept that the programs are accurate when
modeling two different antennas on widely different frequencies.
Please someone tell me why I can model a dipole resonant on 14.2 MHz in the
presence of another dipole 12' away resonant on 13.9 MHz and get a valid
result but I cannot get a valid result if the second dipole is resonant on
7 MHz. At what frequency does everything fall apart?
Now I'm not saying that there will necessarily be a detrimental
interaction, just that modeling will show the effects if there is one.
Which brings me full circle to ask, why not model it and get an accurate
answer rather than relying on "gut feelings?"
Wes Stewart N7WS
>I have to wonder whether either MININEC or NEC-2 handle that kind of
>near-field phenomenon. Just for the heck of it, I may give it a try,
>taking a couple of NBS yagis that are not resonant at any common frequency
>and stacking them (in a model) to see whether they interact anyway.
>
>73, Pete N4ZR
>Contesting is!
>
>The World Contest Station Database
>is waiting for your input at
>http://www.qsl.net/n4zr
>
>
>
>
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