[Towertalk] F12 40M antenna near 10-20M antennas

[Pete Smith]

At 04:05 PM 4/26/02 -0400, Mel Martin wrote:
>Force 12 claims that their 2 and 3 el 40M beams (240M 340M) can be
>mounted within 7' of their C31.
>
>I modeled the Cal-Av 40M, and various 2el and 3el 40M beams within 10 ft
>of a C31XR and various other 10-20M beams, (using EZNEC 3.0) and the
>result always seems to be serious loss of gain and destruction of the
>10-20M pattern. So I'm skeptical about this "within 7 ft" claim. OTOH, I
>had a TH7 10 ft over a 3 el Hy-gain (until the Ice Storm of '98) and it
>seemed to work fine.
>
>Has anyone actually used the 240N or 340N in close proximity to a higher
>frequency antenna, and how were the results?

That IS what Force 12 claims, I believe, for their N elements, used with 
THEIR tribander (the C-31XR).  Presumably, that is based an actually having 
tested the two together.  I don't think you can reason by analogy to the 
Cal-Av 40M/C-31XR combination, or extrapolate to a 240/340N and another 
tribander.

I'm skeptical of how accurately we can model a linearly-loaded antenna 
element like the N element, using NEC-2.  I get really wacky feedpoint 
numbers from all my C-3 models, probably due to the closely spaced 
conductors of differing diameters, and even though I have taken pains to 
align the segments with one another.  With the small conductors of the 
linear loading only inches from the larger elements, it seems as if the 
chances of modeling error are significant.

73, Pete N4ZR

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