I?ve never owned a vacuum variable. What I have been using for decades are
very large air variables hung from a stick, or tree or whatever and I cover
it up with a 2L pop bottle* with the bottom cut out of it. Fix in place
with rope, string, tape, fishing line, whatever.
I can?t take credit for this trick (I don?t think anyways) as I have seen
hardline coax splices made much the same way many moons ago at the famous
VE1ZZ antenna farm.
It?s pretty rare for this to ever fail, or even have wx issues. Of course
if you get screaming high winds with freezing rain going horizontal it is
possible to get a little frozen moisture up inside the bottle and then onto
the plates of the cap, but transmitting a few times usually solves the
problem.
*would the equivalent of 2L pop bottle be ½ gallon soda bottle?
Mike VE9AA
A vacuum variable for L impedance matching is unnecessary. Vacuum
variable capacitors leak eventually. It take a long time for them to
go through their ranges and you have to have the mechanics outside if
you perform remote tuning, to sense or count turns to track when the
v.v. is nearing its maximum or minimum. It is far far easier and
faster to use an air variable that rotates freely. You only need to
keep it sheltered.
Elevated radials are fine provided they are high enough to be
decoupled from earth, which for most hams is difficult to accomplish
on 160 m.
73
Rob
K5UJ
Mike, Coreen & Corey
Keswick Ridge, NB
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