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

Tue, 25 Jun 2002 07:50:23 -0400

At the risk of getting into something that I really know nothing about on a
technical level, let me give you some anecdotal input.  I had 100 feet of
Rohn 45 guyed with quarter inch ehs as follows:  Guy bracket at about 99
feet, thimble, guy grip, 6 inches of ehs, guy grip, 504 insulator (very big
egg), guy grip, then 27 foot non-resonant length sections of ehs repeating.
The antenna was a W2PV 40, 4 el on a 40 foot boom, sitting right at the top
of the tower.  I graphed the SWR change (from about 1.8 to 1 to about 3 to
1) as I rotated the antenna and got a perfect clover leaf centered on each
guy wire.  I replaced the first two 27 foot sections with Philly and the
clover leaf disappeared.  FWIW  73  Saul K2XA
----- 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
> > > >
> > > >
> > > > _______________________________________________
> > > > Towertalk mailing list
> > > > Towertalk@contesting.com
> > > > http://lists.contesting.com/mailman/listinfo/towertalk
> > > >
> > >
> > >
> > > _______________________________________________
> > > Towertalk mailing list
> > > Towertalk@contesting.com
> > > http://lists.contesting.com/mailman/listinfo/towertalk
> > >
> >
> >
> >
> > #################################################################
> > #################################################################
> > #################################################################
> > #####
> > #####
> > #####
> > #################################################################
> > #################################################################
> > #################################################################
> >
>
>
> _______________________________________________
> Towertalk mailing list
> Towertalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk