One more idea on grounding / isolating end elements
on SINGLE BAND Beams:
Place a Parallel Resonant Circuit (at the beam's frequency)
from the element to the boom. The impedance will be
QX= 2 pi F L Q where F = 7 MHz or whatever high band.
At 160M the impedance will be much lower 2 pi F L
where F is 1.8 MHz. The impedance at 40M will be
4 Q times the impedance at 1.8 MHz.
I still think the BEST idea is to just bond the element to
the boom (which F12 endorses).
Tom N4KG
On Fri, 8 Feb 2002 n4kg@juno.com writes:
>
> 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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