I modeled that with the following assumption: that I would ground the 20
meter ref and dir (only) to the boom which is grounded to the mast and
then to the tower . This places the voltage peak out at the end of the
longest and highest elements. That up 13 feet on a mast atop an 80 foot
Trylon self standing tower models to a resonant frequency around 1.7
MHz. I suspect in practice it will be lower than that, say ~1.6 MHz.
Based upon that I'm going to bury a lot of copper around the Trylon,
load it on 160 and deal with what crops up.
-----------------
Guy Olinger
Apex, NC, USA
----- Original Message -----
From: "WA9ALS - John" <wa9als@starband.net>
To: <towertalk@contesting.com>
Sent: Monday, July 30, 2001 1:26 PM
Subject: Re: [TowerTalk] finding resonant frequency of a shunt-fed tower
for 160
>
> I'm interested in this too, so will jump in now. My main question now
is:
>
> I have a C31XR at 72 ft - The elements are -not- grounded. Thus I
assume
> much less (or none?) capacitance hat effect. I therefore assume I can
still
> work out a shunt feed for -some- frequency(s), but they will likely be
> higher freq than if I had grounded elements and therefore more
capacitance
> at the top?
>
> What do you think would be reasonable to shoot for with a 70 ft tower
with
> the ungrounded elements of the C31? 40M? Maybe 80M? Doubt 160M??
Pete,
> I'd be interested in whatever appraoch you end up taking with your
project
> too! Thanks
>
> ----- Original Message -----
> From: Bob Alexander <realex@flash.net>
> To: Pete Smith <n4zr@contesting.com>; <towertalk@contesting.com>
> Sent: Monday, July 30, 2001 11:55 AM
> Subject: RE: [TowerTalk] finding resonant frequency of a shunt-fed
tower for
> 160
>
>
> >
> >
> > Pete,
> > Find a copy of May, 1975 Ham Radio magazine and check out the
article
> titled
> > "How to Design Shunt-feed Systems for Grounded Vertical Radiators"
by John
> > True,
> > W4OQ. I do not think there has ever been a better "how to" article
> written
> > about
> > tower matching.
> > 73, Good Luck
> > Bob, W5AH
> >
> > -----Original Message-----
> >
> > This is my ignorant question for today -- with only an antenna
analyzer,
> > how can I determine the resonant frequency of my tower? I plan to
attach
> a
> > first-attempt at shunt feed at about the 30-foot level, with 30-inch
> > spacing from the tower. Can I tell from the analyzer reading at the
> bottom
> > of that shunt wire where the tower is resonant? Do I need to put
the
> > series capacitance in before attempting the measurement? Or is it
all
> > fruitless?
> >
> > Clearly my education was neglected or I'd know the answer, so thanks
for
> > your help and patience.
> >
> > 73, Pete N4ZR
> >
> >
> >
> >
> > -----
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> > Submissions: towertalk@contesting.com
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> > Problems: owner-towertalk@contesting.com
> >
>
>
>
> -----
> FAQ on WWW: http://www.contesting.com/FAQ/towertalk
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> Problems: owner-towertalk@contesting.com
>
>
-----
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