[Towertalk] Supressors that pass DC control V.

[Jon Ogden]

on 9/26/02 11:50 AM, brewerj@squared.com at brewerj@squared.com wrote:

> I wrote Polyphaser and ICE and both indicated that they do not manufacture
> a HF/KW rated surge supressor for coax, that passes DC (for coax switch
> control).
> 
> I guess I'm going to have to pull some cable through the conduit and fabricate
> another switching arrangement (and then shunt that DC path with some husky
> MOVs)
> to accomplish remote switching with a quality surge arrestor in line.

It was interesting reading the Polyphaser rationale behind this and it makes
sense.

If your tower is hit, there will be lightning energy on both the outer
shield of your coax and the inner conductor.  The energy on the shield will
reach the suppressor first with the inner conductor being delayed because of
the slower propagation velocity factor of the coax.  It will also be spread
out in time.  This time delay will create a voltage potential between the
shield and the center conductor.  If the center conductor has DC continuity
through the suppressor, your equipment will see that potential.  That's the
problem.

What I would suggest you do is make yourself a pair of Bias Tees.  Put one
on the radio side of your suppressor and one after the suppressor.  Connect
the DC feeds together.  Now, you do have a DC continuity still, but if your
inductor is large enough, it should look like an open circuit initially to
the energy of a lightning strike.  Perhaps that still defeats the purpose of
DC blocking in the suppressor.  Maybe someone more qualified can comment on
that.

Alternatively, just use one bias Tee in the antenna side.  Then you just
need to run a DC control cable to wherever your suppressors are located and
you don't need to worry about running a different line up your tower, etc.

Hope this helps.

73,

Jon
NA9D


-------------------------------------
Jon Ogden
NA9D (ex: KE9NA)

Life Member: ARRL, NRA
Member:  AMSAT, DXCC

http://www.qsl.net/ke9na

"A life lived in fear is a life half lived."