Ian Jackson wrote:

From the pictures on the website, 'Coax-Seal' looks exactly like
ordinary self-amalgamating tape (as I know it).

They are quite different. Self-amalgamating tape is a strong,
stretchable tape. 'Coax-Seal' is a form of mouldable putty which just
happens to be supplied as a rolled-up strip, but it has no strength as a
'tape'.

The cut-away picture shows that it does not actually bond to the
plastic outer of the coax, which enables you to open up the connection
in the future.

Coax-Seal does bond to the plastic jacket, and also to metal - in both
cases, well enough to form a good waterproof seal... but if you use it
like the illustration in the ads, you'll have a real mess that is very
difficult to remove from the metal parts.

Self-amalgamating tape is much better in that respect, because it can be
cut and peeled off to leave clean surfaces. For round shapes that are
simple to wrap - like in-line plugs and jacks - it's best to use only
self-amalgamating tape. But for shapes like bulkhead connectors you
can't wrap tape tightly down onto the flange, so water can seep upward
into the connector.

The really useful feature is that Coax-Seal will bond to
self-amalgamating tape! That feature lets you use the best possible
combination of the two methods.

For a cable plug and a bulkhead socket, mould some Coax-Seal around the
base of the socket and a short way up the round part - but don't cover
the whole connector. Then wrap self-amalgamating tape down over the
cable and plug, and onto the Coax-Seal. That gives a very good seal
indeed, and you can cut the tape away at any time to find the metal
parts clean, bright and dry.

I've used these methods for many years on large yagi arrays with many
coax connections, and they do keep the connections totally waterproof.


However, I would still prefer to give the parts a spray of WD40 before
the connections are made, make the connection, spray again to ensure
that the threads are wetted, wipe off the obvious surplus (but not
trying too hard, so there are still traces left). You then apply the
tape, stretching it somewhat as you go, ensuring that you keep a nice,
even tension. You end up with a tight-fitting, waterproof rubber boot
around the joint, with the WD40 trapped inside to resist any tendency
to corrode.
I think the only argument is whether to use WD40 or not.

If the waterproofing works - and it certainly can - then there won't
*be* any tendency to corrosion.



--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek