At 08:15 AM 2/5/2007, you wrote:
>ORIGINAL MESSAGE:
>
>On Mon, 5 Feb 2007 05:33:51 -0500, "K8RI on TowerTalk"
> <K8RI-on-TowerTalk@tm.net> wrote:
>
> >Teflon dielectric is good.
>
>------------ REPLY FOLLOWS ------------
>
>In the aerospace industry our policy was to not use Teflon insulation
>unless we needed its specific properties.
I think the operative word phrase here is "policy WAS to not use Teflon"..
In my part of the aerospace industry (which is deep space oriented),
the only reference to the use of phenolic that I can find is for
ablative heat shields and rocket motor nozzles. Since no PL-259
connectors are used in spaceflight equipment, and as far as I know,
no other currently manufactured space qualified RF connector uses
phenolic for insulation, it's sort of a moot point.
I can see, though, that in a cost sensitive environment, particularly
a few (or more) years ago, the cost differential between phenolic and
teflon would be important. Phenolic/fabric composites (which is
really what we're talking about here) are also used where you need
good mechanical properties, at low cost, with some thermal
insuation. Spacers between manifolds and carburetors, for instance.
And, as far as the venerable PL-259/UHF connector goes.. it
originally used phenolic because it was made by Amphenol (American
Phenolic Company).
>In a PL-259 Teflon is
>overkill.
Probably, but, it's not a big deal either way.
>As I said, use it if you like and it will probably work ok, just try
>to not be seduced by the "gee whiz" factor. Phenolic works fine and
>does not cold flow.
As far as cold flow goes.. The "teflon" in a connector might not be
pure PTFE.. it might have any of a number of fillers (and, besides,
there's different grades of PTFE) that change the mechanical
properties. We use a lot of PTFE based materials for circuit boards
(e.g. Rogers Duroid) and there's a huge variation in mechanical
properties among materials, even while keeping the electrical
properties the same. (You can also get a huge variation in electrical
properties, particularly epsilon, but that's another story)
Jim, W6RMK
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