Have you considered an arrangement to switch between alternate feedpoints
at the bottom of the antenna. Insulate the botom 3.4 - 4 ft of the tubing &
use relays to switch between the lower section while shorting to the top
section or selecting the top feed & isolate the bottom section. I just love
Rube Goldberg constructions like this. could gain you back that fraction of
a dB that you would lose to inductive loading.
At 09:54 PM 7/18/01 -0500, you wrote:
>Many people have responded to my previous post. All responses were quite
>valid and appreciated--thank you. The consensus was to simply cut it for 75
>meters and base load it with a variable inductor arrangement (or variations
>on that theme).
>
>My quest for a top hat switch continues. Why? Because the thing models
>like it will play great!
>
>I'm building an 80/40 open sleeve vertical. It will tune all of 40 at < 1.6
>or so. It will tune all of 80 / 75 if I can get this hat on and off the
>tower. The base loading is the most commonly used and possibly the easiest
>to fabricate. I live in Minnesota and the base will be 5' or 6' under the
>snow in just 6 months. Making a tunable roller inductor arrangement that
>will work in this environment is no simple task either...
>
>How about this option....
>
>Mount a mercury tip switch at the top of the tower in a box on a cam-like
>rotary arrangement (still designing that) and activate a latching
>arrangement using some 1/8" Stainless cable running up the middle of the
>pipe from the base of the tower. I have these little 12 v solinoids that
>will pull several pounds about 1/2". These are details I will work out in
>the shop. My question is, have I simply created a very complicated
>mercury vapor lamp?
>
>The mercury switch is a vacuum. The leads are about 1/4" apart as they
>escape the envelope. At 21 volts per thousanth of an inch (handbook #), a
>1/4" gap should handle many KV. (I only run 1KW max here at this time ~~
>3KV). I know nothing about the conductivity of mercury. For all I know it
>will explode in this environment! A buddy of mine said "Hook it up and
>watch it. If it looks like a strobe light mounted on your tower, you better
>shut it down."
>
>I think I can master the mechanical stuff. What about the switch? Anybody
>venture a guess as to how it will behave to RF as a top hat switch on my 1/4
>wave monopole?
>
>Ford-N0FP
>ford@cmgate.com
>
>
>
>
>List Sponsor: Are you thinking about installing a tower this summer? Call us
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>-----
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Jim Rhodes K0XU
jim@rhodesend.net
List Sponsor: Are you thinking about installing a tower this summer? Call us
for information on our fabulous Trylon Titan self-supporting towers - up to
96-feet for less than $2000! at 888-833-3104 <A
HREF="http://www.ChampionRadio.com";>
www.ChampionRadio.com</A>
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