On 7/25/20 1:02 AM, David Gilbert wrote:
Heliax is essentially plumbing. Quite possibly I simply don't
understand, but why is water a problem? How does it penetrate the
copper sheath?
And if water is a problem, why can't you have a hole in the conduit at
the low spot to drain off the condensation (assuming you're below the
frost line)? The condensation should develop rather slowly, I would
think, because it requires water vapor to penetrate the conduit.
Like I said ... maybe I just don't understand the situation.
73,
Dave AB7E
Daily temperature fluctuations cause air to move in and out of the
conduit - that's where the condensation comes from. Unless you live
where the dew point never goes below the soil temperature, water will
accumulate. Barometric pressure variations do the same thing, but a
lesser effect. Wind causing a small pressure differential between the
two ends also pushes air through the conduit. You'll see this when one
end is outside and another is inside a building, especially if the
building has HVAC with outside air input.
One way I've heard of, but have not seen in person, to fix this is to
run sufficient DC or AC current through the coax to make it slightly
warmer. This sounds like one of those ideas that might work, but then,
it's hard to calculate that it will, and if you've got a commercial
installation, you're more likely to go with something tried and true
(fans, nitrogen purge, etc.). Or in a broadcast environment where
there's significant power flowing through the coax 24/7.
Someone probably tried it in the 30s or 40s, but it didn't work "well
enough"
Running power through an antenna to melt the ice off.. that's been done
a lot - the big Canadian SW broadcast station at the north end of the
Bay of Fundy on the border between Nova Scotia and New Brunswick did
that. Resistive heaters on dishes is also a standard thing.
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