Careful modeling will show that in the presence of non-linear excitation of
the guy wires (like the flux from the antenna cuts more on one end than the
other, as in level tribander and down-angle guys) that the "rules" of
non-resonance fly out the window. All that happens is that the current in
the guy is more out of phase with the induced voltage from the antenna than
one would expect.
Wires, insulated on BOTH ends, shorter than 3/8 wave on the HIGHEST
frequency expected to be used will interact the least of any conductor, the
shorter the better. ANYTHING ELSE in the near field will carry significant
current, REGARDLESS of the length.
A hundred feet of phillystrand cut into three 33' pieces used as the top end
of the top guys will accomplish 90% of what all phillystrand guys will do
for antennas at the top of the tower. If there's a stack on the tower, this
shortcut doesn't work, you really just can't use steel. When you figure out
the relative cost of this 100' of philly, be sure to subtract the cost of
six (or nine) insulators that you won't need in the tower end portion of the
three guys.
When they say that Philly stretches more than steel, true, but put it into
perspective. Philly makes any rope look like a wet noodle or plastic
clothesline by comparison. Maybe they don't use it to guy TV towers, but if
you're worried about the difference between the cost of philly vs. steel &
insulators, you're not putting up anything NEAR what would challenge it.
If you are worried about interaction, go non-conductive. Non-resonant
lengths of steel guy sections (beyond 3/8 WL at highest freq) for
non-interaction are a MYTH. Maybe that's why it's not in the handbook
anymore. Someone has been reading TowerTalk, and checked it out.
Way back in the archives, W8JI did a piece on how much energy transfers
across the egg insulator between adjacent steel sections, which makes the
final performance even WORSE than discovering that non-resonance doesn't
help.
73 & GL on your project,
Guy.
----- Original Message -----
From: "Bill Hider (N3RR)" <n3rr@erols.com>
To: "Mike Gilmer - N2MG" <n2mg@contesting.com>; <towertalk@contesting.com>
Sent: Friday, December 07, 2001 2:38 PM
Subject: RE: [TowerTalk] Non-Resonant Guy Lengths?
>
> It's in the 1994 ARRL Handbook, fig 63, page 36-29
> It's in the 1988 ARRL Handbook, fig 63, page 37-27
>
> Bill, N3RR
>
>
> -----Original Message-----
> From: owner-towertalk@contesting.com
> [mailto:owner-towertalk@contesting.com]On Behalf Of Mike Gilmer - N2MG
> Sent: Friday, December 07, 2001 9:33 AM
> To: towertalk@contesting.com
> Subject: RE: [TowerTalk] Non-Resonant Guy Lengths?
>
>
>
> It's in the chapter called "Antenna Supports" in the
> 18th edition of "The ARRL Antenna Book" in front of
> me. It's doesn't seem to be in the ARRL Handbook that
> I have here.
>
> 73 Mike N2MG
>
> On Wed, 05 December 2001, "Bill Hider (N3RR)" wrote:
>
> > It's in every edition (that I've seen) of the ARRL Handbook.
> >
> >Does anyone know of a web-
> > site that lists which specific lengths to avoid so as not to
> > wind up with guy wires that are resonant on a particular
> > HF band?
> >
> > At one time, I thought I remembered seeing a page in
> > one of my books that listed this but I can't seem to find
> > it. I didn't see it in my Low-Band DX'ing or my older
> > copies of the ARRL Antenna Book.
> >
> > Thanks for the help!
> >
> > 73 de Brad, N9EN @ Radio Free Roscoe (IL)
>
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