----- Original Message -----
From: "Ian White GM3SEK" <gm3sek@ifwtech.co.uk>
To: <towertalk@contesting.com>
Sent: Saturday, July 28, 2007 5:35 AM
Subject: Re: [TowerTalk] Current choke beads
>>Hmmm. I was under the impression that "Teflon" IS "PTFE". I thought
>>that Teflon was DuPont's trade name for PolyTetraFluoroEthylene. Am
>>I wrong?
>
> "Teflon" is a trade name, and can be used however its owners wish.
>
> When PTFE was first invented, both names meant the same thing. But
> DuPont have since developed a much wider range of related materials such
> as FEP (fluorinated ethylene-propylene), all of which may be marketed
> under the "Teflon" trade name.
>
> PTFE is a chemical name that belongs to only one substance. In contrast,
> FEP is a family of materials in its own right. At one end of the range
> are materials with very little propylene in their makeup, which brings
> them very close to true PTFE. Other grades have a lower softening
> temperature (which makes them easier to process) while also being
> tougher and more UV-resistant - just what's needed for a cable jacket.
>
> If a cable is jacketed with a material that feels slippery like PTFE,
> but is even tougher and also more transparent (true PTFE is white), that
> is almost certainly one of the FEP family.
>
> FEP is also used for the inner dielectric in some grades of coax, but
> the softening temperature is lower than PTFE. This makes FEP less
> suitable for cables that have to operate at high temperatures (or at
> high power) and maybe also with a tight bending radius. So when
> CushCraft were designing a new cable specifically for that kind of
> application, it would have made complete sense to specify true PTFE.
>
>
>
>
> --
>
> 73 from Ian GM3SEK
A good choice for toroidal baluns as well as VHF/UHF 1/2 wave baluns is
expanded PTFE (ePTFE) since it is very flexible and does not exhibit the
center conductor flow of solid dielectric. It also exhibits lower loss and
Vp compared to solid.
ePTFE is the choice for test cables in the microwave industry as well as
high speed digital infrastructure in aircraft.
Altho rather expensive to purchase new it has almost no scrap value and
partial reel ends can often be found in trash piles at some companies or
scrap dealers.
Ive found sufficient quantities within 5 miles of here to last me a very
long time and the price was right.
Carl
KM1H
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