[TowerTalk] Top Hat Switch (mercury)

n4kg@juno.com n4kg@juno.com
Wed, 18 Jul 2001 21:56:06 -0600


What's going to keep the snow off the top hat / switch / 
top of vertical?

You really don't need a roller inductor at the base, just
switch a fixed inductor (which you pretune).  If you don't
like inductive loading, tune the vertical for 80M CW and
switch in a fixed series capacitor for the SSB portion of
the band.

Tom  N4KG

On Wed, 18 Jul 2001 21:54:22 -0500 "Ford Peterson" <ford@cmgate.com>
writes:
> 
> 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
> 
> 
> 
> 
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