[Towertalk] Guy wire resonance. Break it up or use stubs?

Tue, 25 Jun 2002 02:21:35 -0400

Guy,

All the points you are making, I have never heard anyone complain about,
including the 486/f "thing".  What, BTW, is that all about?  That formula is
an approximation.  I've used it for years and never had a "problem".  That
doesn't mean it's accurate -- it just means that it gets you close, then you
take into account your situation and go from there. Is that the 486/f
"thing"?  Where is the 486/f "thing" (problem) documented?

I have never heard anyone say that the weirdness went away when they
switched to fiberglass/Phillistran, either.

Not that my not hearing about it means it's wrong.  No, I'm not saying that.
What I am saying is that, since this is the first time I've heard anyone say
what you've said, and I've been a ham for over 40 years and plugged into
publications, listserves and clubs where these types of things might be
brought up, I'm wondering if it's a wide-spread problem or not.  I suspect
not, since I've not heard of it.  And if it's not widespread, what then?

I do use EZNEC.  I don't know about the F12 antenna problems - I don't have
any of those antennas.

I did investigate all this in 1991/92 when I designed my new antenna system.
I consulted well-known contesters, antenna design books, ARRL publications
(including many editions of the Handbook, other ARRL antenna publications)
and antenna and tower manufacturers. Nowhere did I find discussed any
"problem" with the non-resonate lengths in the Handbook, or the fact that
breaking up guy wires that way "won't, or doesn't work".  Expensive, yes -
but not that it wouldn't work.

I think you can model any wire in the nearfield and induce current, this
includes an 80M inverted "V" in the near field of a 40M dipole.  But does it
really matter?  And can you do anything about it anyway (the 80/40M
example)?

So, I'm still skeptical.

Who out there has had problems with insulator broken-up guys that were
corrected by using Phillistran or fiberglass?

Bill, N3RR

----- Original Message -----
From: "Guy Olinger, K2AV" <k2av@contesting.com>
To: "Bill Hider (N3RR)" <n3rr@erols.com>; "tongaloa" <tongaloa@alltel.net>;
<towertalk@contesting.com>
Sent: Tuesday, June 25, 2002 12:17 AM
Subject: Re: [Towertalk] Guy wire resonance. Break it up or use stubs?

> Yup, fiberglass if you know to manage the sproing and have some way to
> deal with the minimum order business. Good stuff.
>
> What kind of commercial installations?
>
> AM radio stations stay away from dipole resonances in their guys by
> keeping sections that by eyeball measurement are a 1/10 wave or less.
> And they only operate at one frequency. So whatever induced weirdness
> can be just tuned out at the transmitter.
>
> Bob could do the same at the highest frequency in use and that would
> work, but could he afford all the insulators and big grips? Would he
> want to look at it?
>
> The insulators I see in use by hams in their guy wires are those three
> or four inch egg insulators which have plenty enough capacitance to
> induce end-effects.
>
> Do you have EZNEC 3? I can feed you a couple of models with ARRL
> lengths in them and ask you to explain why there is so much current if
> the wire isn't "resonant".
>
> And this isn't material that is on the bleeding edge of NEC abilities.
> Just plain wires in each other's near field. No rocket science at all.
>
> For a preview, have you ever seen the current distributions on the
> different conductors in a Force 12 XR feed cell? 15 and ten meters
> both induce a smooth end to end SINGLE PHASE current in the 20 meter
> element. According to the ARRL stuff the 20 meter element is not
> resonant at 15 meters. So how come the current? Near field effects. A
> whole spectrum of interesting phenomena that explains why a C31XR
> actually works.
>
> If the two elements were at a distance, the difference between 15
> meter and 20 meter induced current in the passive 20 meter element
> would be substantial, ergo the ARRL specification.
>
> I can't explain why it isn't broadly complained about. It's just as
> obvious as the 468/f thing. I never heard the 468/f thing complained
> about until after I personally got stung by it.
>
> You still think that for something to be true it has to come from a
> reference? Mostly, yes, but then how does anything get changed or
> moved forward?
>
> You can use the maturity of NEC on simple wires in free space as a
> "reference". You can use that a C31XR works at all as a reference.
> Other than that, you have another human being standing in front of you
> saying that the ARRL resonant lengths are a "myth".
>
> It would be completely amazing to me if I was the first one to suspect
> problems in the ARRL resonant lengths scheme. But however unlikely,
> suppose I was the first? Should it make a difference?
>
> Anecdotally speaking, if the scheme actually worked, how come so many
> hams have reported weirdness going away when switching to Philly or
> fiberglass, or those twenty foot insulators. If the scheme worked why
> would anyone bother with Philly? Shouldn't persistent, unexplained
> anecdota make one suspicious?
>
> 73, Guy.
>
> ----- Original Message -----
> From: "Bill Hider (N3RR)" <n3rr@erols.com>
> To: "Guy Olinger, K2AV" <k2av@contesting.com>; "tongaloa"
> <tongaloa@alltel.net>; <towertalk@contesting.com>
> Sent: Monday, June 24, 2002 11:23 PM
> Subject: Re: [Towertalk] Guy wire resonance. Break it up or use stubs?
>
>
> > For completeness, when looking for guy wires that don't interfere
> with HF
> > antennas, you need to look at fiberglass guys as well.
> >
> > In the quantity I used, they were cheaper than Phillistran and
> cheaper than
> > breaking up the guys with insulators every 11 feet (the ARRL number
> for no
> > ham-band resonances).
> >
> > There is some detailed info on my website: www.erols.com/n3rr
> >
> > BTW, Guy, what is your reference for the statement: "...ARRL
> anti-resonant
> > sections are a myth"?  I had not heard anyone "complain" about this
> before
> > and capacitive coupling may be reduced to negligible by increasing
> the
> > length of an insulator.  Far more commercial tower sites than hams
> use this
> > method.
> >
> > 73,
> >
> > Bill, N3RR
> >
> > ----- Original Message -----
> > From: "Guy Olinger, K2AV" <k2av@contesting.com>
> > To: "tongaloa" <tongaloa@alltel.net>; <towertalk@contesting.com>
> > Sent: Monday, June 24, 2002 10:50 PM
> > Subject: Re: [Towertalk] Guy wire resonance. Break it up or use
> stubs?
> >
> >
> > > I've spent as much time as anyone worrying over guy wire
> resonances.
> > >
> > > The ARRL anti-resonant sections are a myth. They don't work
> because
> > > the guy wires are in the antenna near field and currents are NOT
> > > evenly induced across their length by a distant (far field) point
> > > source, apparently an unintended assumption in the ARRL figures.
> They
> > > further don't work due to capacitive feed across breakup
> insulators
> > > that changes the length in a non-predicted way similar to
> end-effect
> > > on dipoles.
> > >
> > > I'm not sure what construct you mean by transmission line
> sections.
> > >
> > > If you can afford it (do the comparative cost math on insulators,
> > > grips, etc) get Phillystran. Or maybe do the first 33 feet of
> every
> > > guy off the tower in Phillystran.
> > >
> > > Sleep at night.
> > >
> > > 73, Guy.
> > >
> > > ----- Original Message -----
> > > From: "tongaloa" <tongaloa@alltel.net>
> > > To: <towertalk@contesting.com>
> > > Sent: Monday, June 24, 2002 2:13 PM
> > > Subject: [Towertalk] Guy wire resonance. Break it up or use stubs?
> > >
> > >
> > > > What's the word these days on guy wires.
> > > > Break 'em up with insulators or make up transmission line
> sections
> > > to get
> > > > away from
> > > > resonance near operating freqs?
> > > > Thanks,
> > > > -bob
> > > >
> > > >
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