Dan,
You can examine the stub-tuned reflector behavior using the EZNEC
Transmission Line feature.
The K3LR et al approach looks best to me, with the reflectors tuned for
maximum smoke, but there are enough variables in a practical installation
that might make it hard to detect the extra few dB F/B or tenths of a dB
gain over the other designs.
As you work on this, remember the law of diminishing returns (speaking from
experience): If an array has a modeled gain of 4 dB, you will get 3 dB
easily, then 3.5 dB with some careful additional work -- getting all 4 dB
takes some combination of skill, luck and preseverance. Some guys don't do
perseverance, and are quite happy with 3.5 dB.
73, Gary
K9AY
> Design criteria:
> - 3 inverted vee elements, standard #14 or #12 insulated wire fed in the
> middle
> - Ground the unused 2 elements. A friend advises that especially here in
> FL that "floating" the unused elements will allow them to build up a
> charge,
> thus attracting lightning, so I should ground them instead.
> - Mount on an 87' tower that also has 5 HF Yagis on it. Guys are broken
> up with insulators. The downside of this is that the tower is a few feet
> short for allowing the vees to have the ideal included angle of 90 deg.
> - Use RG8X Mini for the feedlines to the switch box, along with the K3LR
> method of beads over a 14" section of thin coax at each feedpoint.
>
> I downloaded the demo version of EZNEC last night and enjoyed learning it
> tremendously. Wow, Roy -- what a full-functioned app! Anyway, the
> learning curve for entering the wires was not bad at all and I soon had
> the 3 vees
> in their sideways positions around the center, all fed in the middle.
>
> But as soon as I got to the Holy Grail problem of how long to make the
> feedlines, I hit my roadblock and don't know how to proceed.
>
> Here's what I've found published to date:
> - K3LR/WA3FET/K3LC design uses 4 sideways vees, floats the unused ones
> (does that matter?), and uses 153.45 degrees of feedline on each element.
> Their ELNEC design was quite precise and thorough. Circa 1992. Full
> article
> in Antenna Compendium Vol 4. See p.11 in particular.
> - K1WA 5L half-wave sloper array uses 135 deg of feedline and opens the
> unused lines. This design goes back to the '70s and was published in many
> ARRL Antenna Books.
> - W7LR built a 4L 40 array and also concluded that using 135 deg was
> correct. See Feb 1995 QST - Tech Correspondence.
>
> Side note - RG8X VF is listed as 0.75 and 0.78 in various places. This
> is
> trivial, since it just gives a starting place from which to trim more
> precisely.
>
> I'm grateful for any input and assistance on this and hope it's a
> worthwhile pursuit vs. just separating the flys*** from the pepper!
>
> 73, Dan, K1TO
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