[Microwave] Clamping hardline to towers & water proofing (greasing) RF connectors

[Dr. Gerald N. Johnson, electrical engineer]

The makers of hard line coax make hardware specifically for holding
their cables to towers. Some are insulated, some are not. Some are more
permanent than stainless steel hose clamps, some are their brand of
stainless steel hose clamps.

Type N connectors have gaskets intended to keep water out. Using UHF
connectors at UHF gets water in.

Connectors have been filled with mostly silicone dielectric greases to
keep water out. Other greases may have significant losses at RF and
microwave. I don't know of tests of those greases. I think it was Ken
Britain who suggested mixing in hollow glass microballs into the
silicone dielectric grease to lower its dielectric constant and so make
less of an impedance bump in the type N connector that is matched best
when filled with air. That was published in a MUD or CSVHF Conference
proceedings a few years back.

I use an aluminum conductor grease when mounting brass adapters to CATV
aluminum cable. Its worked fine for decades.

If you clean off the excess grease, Scotch #33 or #88 stick well. Other
black electrical tapes are often far poorer than the real Scotch
product.

It is getting hard to find, but a combination of Scotch #33 and
Scotchkote yellow goo with three to five layers of each makes a cable
waterproofing that works very well. I've cut open such connections after
years underground and the connections inside were pristine.

The modern heat shrink tubing that melts inside to make a tighter seal
is the replacement for multiple layers of tape and Scotchkote. There are
also shrink tubings made with a coiled support that when pulled lets the
tubing shrink and seal the connection suitable for direct burial. A
sealing scheme that works for aluminum service entrance cable
underground below the water table will work fine for sealing coax
connection above ground.

73, Jerry, K0CQ
-- 
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.