RE: Topband: Re: Coax capacitor losses

[W0UN -- John Brosnahan <shr@swtexas.net>]

Whenever I have needed a capacitor in a hurry, such as on a DXpedition
or during a contest I have used coaxial cable.  If the amount of capacitance
is very high, say, a few hundred pF, then I use a number of short lengths of
cable in parallel.  Saves having to work out the transmission line equations
for a cable that would be an appreciable part of a 1/4 wavelength.  If I need,
for instance, 180 pF, then I may use three, 2-ft pieces of RG-213 in parallel,
or even, six 1-ft long pieces in parallel.  Just makes life simpler, 
especially
when under time pressure or limited component availability.

I have also made low/mid VHF matching caps by paralleling short lengths of
twisted-pair wire made with Teflon-insulated, hookup wire.  I have been 
doing this
with phased arrays of coaxial-collinears at 138 MHz.  When you are doing a
research project in the boonies in Alaska or Chile or Antigua you make do with
what you can get.

--John  W0UN


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