From: "Barry L. Ornitz" <ornitz+U@dpnet.net>
Subject: Re: Silicone dielectric grease for waterproofing?
Date: 13 Apr 1999
Newsgroups: rec.radio.amateur.antenna

nero_b@my-dejanews.com wrote in message
<7etv47$k92$1@nnrp1.dejanews.com>...
>I have been using silicone dielectric grease on the outside of my coax and
>antenna connections for waterproofing. It seems to do a good job and I
>like it better than the waterproofing tape.


Silicone grease repels water much as an oily surface does.  However, it
does not stop the ingress of water vapor very well.  You still need a
pretty good antenna or connector connection.

>I recently was running a TV antenna and purchased waterproof F connectors
>from radio shack. It appeared that these had a bead of dielectric grease
>in the pathway for the shield. This made me wonder if I could squeeze
>dielectric grease inside my coax connections to waterproof from the
>inside out?
>
>Will this change the impedence of the connection? Does this grease
>function as a conductor, insulator or something in between?
>
>Also, in the past I have seen advertised a coax waterproofer that was
>designed to be put right in the connections before assembly. The claims
>were that it would not change the impedence and keeps water from getting
>into the connections. Does this stuff work as advertised? Where to get
>this stuff?

The presence of silicone grease where the connector expects air will cause
the impedance to drop over the short distance.  Unless you are pushing the
connector to its upper frequency limit (generally in the microwave region
for BNC, N, and other constant impedance connectors), the effect will be
slight.  UHF connectors are so poor, adding the silicone will likely not be
noticeable.

The grease is an insulator.  If it coats electrical contacts, it can
prevent electrical continuity.  However, if the contact is tight
mechanically, the grease will be forced out of the connection and
continuity will be maintained.

I generally use silicone stopcock grease from a chemistry lab, although GE
and Dow sell many other versions.  A good plumbing supply may carry them.
[Remember this is not silicone bathtub caulk.]  The white silicone heatsink
compound is ordinary silicone grease containing zinc oxide to improve its
thermal conductivity.

If you use the silicone grease on antennas, assemble the antenna first with
good, clean surfaces.  Apply the silicone after assembly.  As someone
noted, greases containing zinc particles are useful when bolting aluminum
surfaces together (Penetrox).  These are usually not silicone greases which
are far more expensive.

A thin coating of silicone grease on the surface of polyethylene twinlead
or ladder-line will help prevent ultraviolet degradation of the
polyethylene and it will restore the water repellency giving a slight
decrease in loss when the line is wet.

Coaxial cable designed for direct burial often contains a silicone oil
impregnating the braid.  If the outer jacket is pierced, the oil prevents a
rapid ingress of moisture (but the moisture eventually works its way in
anyway).

        73,  Barry L. Ornitz     WA4VZQ     ornitz@dpnet.net