I understand all of that. Water vapor will penetrate the walls of the
conduit and condense inside, or as you say, get inside via air flow
through the conduit. But why is that a problem for the Heliax inside
the conduit? Assuming the conduit is below the frost line, of course.
73,
Dave AB7E
On 7/25/2020 6:01 AM, jimlux wrote:
On 7/25/20 5:41 AM, jimlux wrote:
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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