|To:||email@example.com, "Tom Rauch" <firstname.lastname@example.org>|
|Subject:||Re: [TowerTalk] 80 4-square inside a 160 4-square? Pros andCons please!|
|From:||Jim Lux <email@example.com>|
|Date:||Fri, 11 Jun 2004 10:25:14 -0700|
At 09:58 AM 6/11/2004 -0700, Rick Karlquist wrote:
> The function of that network is to ground the 160 elements > for 80 meter signals while parallel resonating on 160 so it > is open circuit on 160.
It might be tedious, but, given that the 160m elements (switched, trapped, whatever) are going to have some effect on the 80m patterns (traps,switches, etc. can reduce, but not eliminate the effects), is it possible that you could do an integrated design. It's not as simple as just laying an 80m design on top of a 160m, but, fundamentally, I can't see why such a design cannot exist. There's probably some arrangement of the elements that would produce perfectly acceptable results.
For example: This might not be practical for other reasons, but say you wanted to superimpose two 4 square type arrangements. You don't have to line up the elements. One set of 4 could be 45 degrees from the other set.
There's also nothing that says that the center of the squares have to be collocated. Maybe one element is a "dual band" 80/160 vertical.
Finally, if you have enough room (would that this is case!), one arrangement might be to put the higher frequency elements OUTSIDE the lower frequency ones. Say, you built an 80 m 4 square (20m on a side). Then, you put up the 40 m foursquare elements outside the 80m elements, but still spaced an odd multiple of 1/4 wavelength apart (i.e. 3/4lambda, or 30m or 5/4-> 50m apart).
In any event, I find it hard to believe that you can't find SOME arrangement of the elements for the two bands (within a square defined by the larger elements) that doesn't have the right spacing and drive impedances and combined patterns that would work.
Clearly, this is a job for some sort of optimization program. There are a number of free general purpose optimizers out there that can run any modeling program (e.g. GENOPT). The trick would be in defining an appropriate figure of merit to optimize. With Yagi-Udas or Log Periodics for instance, there's a long history of manual optimization which helped to define useful figures of merit (F/B, VSWR bandwidth, etc.), so that when automatic optimizers came along, it was fairly straightforward to create appropriate "objective functions". The same cannot be said for phased arrays, which have directivity and operational characteristics (and constraints) that are different from the "multiband beam on a tower" paradigm.
If anyone's interested in this kind of thing, I've got a bunch of programs that can parse the output of NEC, and other programs that can do things like measure beamwidth in the parsed output. They're in a combination of VB, C, and Matlab.
GENOPT can invoke a script/batch file which would have:
Modelbuilder -> takes parameters being varied and generates a NEC input file NEC Parser -> extracts data from NEC output Evaluator -> uses parsed output to create figure(s) of merit
If someone were to suggest a suitable objective function/figure of merit for such antennas, I'll take a shot at doing the optimizing. By the way, if someone has a little program that can do symbolic substitution and generate models into a NEC model file(like 4nec2 does with symbols), that would be really handy. This would particularly handy if it can handle symmetry nicely.
Hmmm.. maybe something like an XML high level description of the antenna system that gets turned into appropriate NEC cards.
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA.
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