...and the answer (from F12) is:
--------- Forwarded message ----------
From: "Force 12" <force12@fix.net>
To: <n4kg@juno.com>
To: <towertalk@contesting.com>
Date: Fri, 8 Feb 2002
Subject: Re: [TowerTalk] Shunt Feed Capacitor for Tower
Since the issue is the end elements, connect them directly to the boom.
This can be done by omitting the insulating PVC (remember not to crunch
the tubing), or by adding a shorting bar/wire to the boom. Have suggested
this to two people over the years who were using a shunt-fed tower.
No problems. A relay is one more thing that can go wrong and it
is really hard to get to.
73, Tom (N6BT, Founder of Force 12)
----- Original Message -----
From: <n4kg@juno.com>
To: <TOWERTALK@CONTESTING.COM>
Cc: <force12@fix.net>
Sent: Friday, February 08, 2002 11:30 AM
Subject: Re: [TowerTalk] Shunt Feed Capacitor for Tower
> N4KG response below.
>
> On Fri, 08 Feb 2002 Pete Smith <n4zr@contesting.com> writes:
> >
> > At 11:34 AM 2/8/02 -0600, n4kg@juno.com wrote:
> > >
> > >Another solution to the high voltage problem at the
> > >insulated end elements of F12, KLM, and X7 / X9
> > >antennas would be to install a relay to short the
> > >center of the end elements to the boom when
> > >you want to use the tower as a vertical, leaving
> > >the relay OPEN when you use the beam.
> >
> > I'm a little leery of serendipitous resonances and unexpected
> > interaction
> > that could result if you short elements and boom together. Wouldn't
> > it make better sense to connect a small inductor between the element
> > center and boom (thanks W8JI), such that it looks like a short at
160m
> but
> > an open at 40m and above?
> >
> > 73, Pete N4ZR
> >
>
> With only a 4 to 1 frequency ratio, I expect it may be a little hard
> to make even an 'ideal' choke that will look like a short at 1.8 MHz
> and an open at 7 MHz since X = 2 pi F L. At 14 MHz, you have
> an 8 to 1 ratio to work with which is quite a bit better, as long as
> you be careful to keep the self resonant frequency of the choke
> above 28 MHz.
>
> I think my relay suggestion makes a better OPEN and SHUT case :-)
> for those who are concerned about boom currents when using the Yagi.
> I wonder what F12 has to say about just connecting the end elements
> to the boom to prevent arcing when using the tower as a 160M vertical?
>
> Tom N4KG
>
>
>
>
>
>
> ________________________________________________________________
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