Pete Stark K4OM wrote:
> Does anyone know the proceedures and materials needed to form molded
> junctions (Tee's generally) from rg11 and rg8 size cable. I have a harness
> to re-do for an 8 pole 2 meter repeater antenna and I do not trust coax
> connectors or coax Tee's at 900 feet. The last harness lasted 25 years and
> it was of the molded type. Thanks
Are you talking about potting, say in silicone? You get the appropriate
two part RTV (Newark, etc. carry it) and get some suitable forms and
cast it. The key is being able to pump a vacuum on it.. you need to put
the cable into the chamber and pump it down first (to remove the gases
in the tiny space in the shield and between dielectric and conductors),
then you add the potting compound, and let it cure.
Your RTV needs to be a very slow cure type (because you have to mix it
up before you pump down, so it can degas before you pour).
If you use a thermally cured plastic, rather than an RTV, you can pump
down, then heat it up to cure. I think that's what the commercial cable
companies use, but they've also invested in the tooling and process
experimentation to get the right material and temperature profiles. You
could go through a few dozen shots before you get it right.
Actually, if you're not worried about high voltage/high power breakdown,
you could probably skip the degassing by pumping down part, and just
cast the joints in epoxy, urethane, or RTV silicone. The key, I
suspect, will be getting a good bond between the potting material and
the jacket material of the coax, which is more a matter of choosing an
appropriate cable and/or surface preparation (e.g. if you have a
polyethylene jacket, it's hard to get stuff to stick to it).
In the past when I've done this sort of thing, I've spent some time at
the store (Sil-Pak) that supplies the potting compound talking to them
about the appropriate thing to use, given what I was potting, the cure
time, and so forth. This is generally not something where you want to
go to Home Depot and trust in the guy/gal with the orange vest.
I've seen people use plastic plumbing fittings as molds.. they're cheap,
etc. It's not as nice looking as a neatly tapered mold, but it's
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