+, when waveguide, and/or coax leaks, even a SMALL amount of water has a
profound effect on it's ability to move rf! Remember several instances of
water inside waveguide, only say, 1/16 th of inch deep, on top of window (a
dam of either mica, or teflon, to act as a vapor barrier), completely
absorbeing all signals, both ways at 6 GHz! Modern systems tend to use dry
air pumps (andrew, Prodelien), but even telephone cables (copper, with
plastic, and paper insulation) are often pressurized. And, as an aside,
when moisture has penetrated these, oftentimes, the pitcock on one end
(lower, or level) is opened, while nitrogen, or dry air is applied to the
other end, and allowed to continusly flow thru it, to dry it out, or at
least to keep it going until favorable weather appears, to timely replace
it! and, IF you look at waveguide fittings (both rectangular, and round,
the first gap (if you will is a 1/4 wave choke, , and there is usually a
SECOND ring (both recessed) , that an rubber gasket fits in for an air
block. the wave guide that it mates to on the other end has only an opening
for the waveguide, itself, forming (when both these ends are properly mated
, an airtight, and rf tight connection . and to insure correct fitting of
them, the screw holes of one (forget which) are threaded, and the other is
NOT (only one way to apply them! ) --Jim NN7K

--
No trees were killed in the sending of this message. However, a large number
of electrons were terribly inconvenienced !

" People who never get carried away, should be! " --- Malcom Forbes

"Roy Lewallen" wrote in message
...
In the '60s I worked on heavy ground radar, which produced peak powers
of several megawatts. The waveguides for those antennas were routinely
kept slightly pressurized with dry air. In the set I worked on the most,
the air was pumped through one of two canisters of silica gel dessicant,
while the other was being heated and purged of accumulated moisture. The
roles of the two canisters was automatically and periodically reversed
to assure a continuing supply of dry air. A small hole at the antenna
end of the feedline allowed a little air flow to occur. In some climates
at least, the waveguides would internally arc if the dry air supply
failed.

Roy Lewallen, W7EL

Irv Finkleman wrote:

Russ wrote:

It's probably "dry" N2. It is used to prevent water absorbtion and O2
absorbtion of the RF. It can also be used to detect leaks and to keep
out atmospheric water.

Russ


Exactly! Very common in some of our shipboard antenna tuning units as
well -- at least back in the 70's.
Irv VE6BP