[TowerTalk] C31 ant file - query

[Pete Smith]

At 05:06 PM 2/23/2000 EST, K7LXC@aol.com wrote:
> ...
>
>      The newest generation of antenna electrical designs have been designed 
>with computer modeling and the NEC program. With this ability to really 
>scrutinize a design (along with being able to run literally hundreds of 
>iterations), sometimes a quarter-inch dimension difference can cause an 
>unwanted change. And that's particularly true with the newest sleeve feed 
>systems; they are dimensionally critical. 
>
>      And, yes, I think the sleeve feeds in F12 antennas should have some 
>sort of device to hold the elements in place because they DO move in the
wind 
>and the SWR DOES change. 


I think you're both right, but maybe Terry more so.  A quarter-inch change
in dimensions doesn't cause a SIGNIFICANT change with either of my Force 12
antennas - a C-3 and an EF-240S.  Yes, I can see the SWR wiggle with when
the wind blows, but it's a curiosity, not a problem.  And of course, since
models use perfectly straight elements, no model represents reality (and
elements with sag) to a quarter-inch tolerance, at least for HF antennas.

Also, Force 12 has included spacers on some of its more recent closed
sleeve antennas, though I suspect they are more a marketing device than an
electrically needed change...

73,  Pete N4ZR

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