[TowerTalk] Shunt Feed Capacitor for Tower

n4kg@juno.com n4kg@juno.com
Fri, 8 Feb 2002 13:30:55 -0600

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
> 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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