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
> >
>
>
>
> #################################################################
> #################################################################
> #################################################################
> #####
> #####
> #####
> #################################################################
> #################################################################
> #################################################################
>
|