Guy,
I think if you look back a few years (perhaps 20-25), the whole theory of
guy resonances was first mentioned and explored by the late Jim Lawson,
W2PV, and I think he provided the info that is now in the ARRL references.
Furthermore, none of the so called WARC Bands (12, 17 and 30 meters) were
in existence at that time.
As for the 468/F formula, that is for a half wave wire with insulators on
the each end. the assumption here is that the insulators shorten the wire
by 5%. No magic but a loose approximation for the simplest cases as we all
now know.
73,
Joe, W1JR
At 12:17 AM 6/25/2002 -0400, Guy Olinger, K2AV wrote:
>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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