N fittings & sealing & weatherproofing

[Steve Uhrig]

Hi All,

While we're discussing sealing antennas and stuff, I'd like to throw my
nickel in.

My work takes me all over the world, doing field expedient communications
intercept systems for military, in deserts and jungles. People die if
these systems fail.

First, I buy all coax and connectors from Joel at RF Connection.
www.therfc.com. I use 3 piece crimp connectors where possible. I prefer
BNC or N, depending on the freq, or SMA if microwave.

I fill the insides of all connectors with a teflon-based compound called
STUF. I get it by the case of 144 tubes from the manufacturer, but it is
sold by some of the ham dealers. It looks like a toothpaste tube made of
plastic, and has a weird coupling nozzle that will fit most connectors.
You simply squeeze the slimy white stuff into the voids of both halves of
all connectors, displacing all air, then assemble the connector. Yeah,
the stuff will squirt out, and you want this. You want no voids in the
connector. No air space. A rag will wipe it off well enough to continue.
One tube of STUF costs around $2 (in my quantity) and will do 20 or more
connectors.

Then I wrap Scotch 33M+ tape around the connector, from 3 or 4 inches
below the connector on the coax, overlapping 50% and stretching somewhat,
up to the body of the connector the best I can. As mentioned, cut the
tape leaving no tension on the final wrap. I then secure the end of the
tape around the connector with a small wire tie, and cut off the tail.

Then, I use liberal amounts of Coax Seal, from below the end of the tape,
wrapped 50% overlap, up to the connector. I mold the Coax Seal around the
connector and press it into any voids and up around everywhere so no
metal is exposed. If working in a cold climate, I keep the Coax Seal in
an inside pocket to keep it malleable.

That does it. I've opened up connectors after years in the desert in
Bogota, and there's absolutely no moisture. The Coax Seal removes cleanly
because of the tape layer underneath, and the 3M tape unwinds neatly.

STUF does not have any problem up to 6 gig microwave. I've swept cables
and connectors done this way on a TDR, and you barely can see the
impedance bump, to several gigs.

None of this is expensive, or complicated, or difficult to do even on a
ladder when you're hanging on by your ears and holding a flashlight in
your teeth in 30 mph winds. For maybe USD $3, I can secure an antenna
connection on a critical commo system against the elements in some of the
roughest terrain imaginable, for a decade.

More than anything else, I recommend STUF and Coax Seal. Maybe your club
can buy in industrial quantities and get a price break, although none of
it is expensive. STUF also is superb for installations near the coast,
with a salt water environment. No green crud if you do it right.

I know also Radio Works www.radioworks.com sells Coax Seal and Stuf. I'd
try RF Connection first, though.

Thanks to all for helping me get the most enjoyment out of my beloved K2.

Steve WA3SWS K2 s/n 661


*******************************************************************
Steve Uhrig, SWS Security, Maryland (USA)
Mfrs of electronic surveillance equip
mailto:[hidden email]  website http://www.swssec.com
tel +1+410-879-4035, fax +1+410-836-1190
"In God we trust, all others we monitor"
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