> de K6NA 2 April
> Towertalkians interested in guy wire effects on sidemounted Yagi antennas
> might like to read of my experiences. I've been conversing with Steve,
> KJ7CH about Nico-Pres tools, etc. and decided to mention a couple of related
> things to him, hence this note to TT.
> Good deal Steve, glad you are a swaged-fitting convert. You will be happy!
> One note: practice pushing the sleeve just "the right" distance along the
> wire, next to the ceramic insulator. If it ends up too loose, the insulator
> can flop or get partially turned before you tension the guy. If it's too
> tight (too close to the insulator), you can actually break the insulator as
> you install the sleeve, because the material creeps or elongates a bit while
> you make the multiple presses required, and the wire loop can get too tight
> around the ceramic. "Just right" is snug, but not broken.
> Ok about the JA version. The Nico-Pres brand name is used by I think the
> American Telephone Supply Company from Ohio. And it is absolutely great
> quality... I don't think the JA's can improve on it, but could certainly
> equal it.
> Only thing is, be absolutely certain that their sleeves are CORRECT for your
> wire size... wouldn't they be making a millimeter-type tool whereas we spec
> all our wire in inches?
> An electrical note: Everyone including the Antenna Book says we can make
> the wire guy sections 27-29 feet long between insulators. I built my two
> 140-foot towers using that method. I had a 3-foot pigtail from the tower
> guy bracket to the first insulator, and then 28-foot sections all the way to
> the ground. Well, my 20 meter stacked array of two 5-EL yagis did not work
> correctly. The top antenna is at 140 feet, and the lower identical one is
> just above the 60-foot guy level on a rotating sidemount. The guy radius is
> 105 feet. This means the 60-foot guys are very "flat-looking", i.e. almost
> "horizontal". The KLM driven elements of the lower beam are right out over
> these guys, and after observing what was going on, I had to make changes.
> Turns out the beam was really coupling to the 28-foot wires right under them
> (like inefficient directors!). This messed up the pattern, and there were
> three broad but distinct bulges (every 120 degrees) in the VSWR curve of the
> lower antenna as I turned it around the tower.
> The fix was tedious but successful. I rebuilt the upper portions of those
> nearby guys, one at a time. I installed more insulators, so that each
> 28-foot wire became three nine-foot wires, in the area near the beam. I did
> this on both the 60- and 90-foot guy levels. The lower beam, and thus the
> stack, then worked correctly. There is also a 15-meter beam on a sidemount
> just above the 90-foot guy bracket, so the additional break-up of the
> 90-foot-level guys is probably helping that antenna also (it really works).
> Note that 28 feet is something over a half-wave on 15, so there is a big
> chance of coupling there too, I think.
> I related my experiences to K6STI a few years ago. He became interested in
> the problem, and ended up writing his guy wire analysis program. I had
> fixed the problem already, but he told me that the model did in fact show
> the problem.
> Bottom line: Within about, say, 50 feet of the tower legs I recommend guy
> wire insulators every nine feet if you are using side-mounted yagis, alone
> or in stacks. Beyond about 50 feet out, I don't think it makes much
> difference, 28 foot lengths are probably fine, or even no insulators at all
> are probably o.k. in those lower areas far out from the antenna (unless you
> also have some vertical arrays in the vicinity...but that's another matter).
> Sidebar: Slope angle of the guy obviously has something to do with the
> amount of potential coupling. That's why the top antenna on a tower usually
> works fine even with no insulators at all in the guys. The top set of guys
> slopes steeply away from the vicinity of the yagi and coupling would be
> minimal. Modeling fans can look at these things and decide.
> 73, Glenn K6NA
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I went with 3/8" fiberglass guy rod made by Polygon (13,000# breaking
strength). Glass grips (like Big grips for steel) at each end attached
to standard guy hardware is cheaper than insulator-broken-up-steel or
Philistran. And it is NON-conducting, not just "insulated", which means
zero-effect on my 4 (soon to be 5) ring rotor mounted antennas, plus
zero inductance for lightning (like Philistran)!!
P.S. Several of us PVRCers and a couple of FRCers also use fiberglass
guy rod to eliminate interaction with our "antenna-loaded" towers.
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