Add these to Harold's list of suitable dielectric materials at 50 MHz
or up to a few hundred.
Crosslinked polystyrene (Rexolite), Ultra High molecular weight
polypropylene, polyester (polyethylene terephthalate), Polyetherimide
(Ultem, Thermalux), Polysulfone (Udel), Polyimide (Vespel, Envex), G7
glass/silicone laminate. I stay away from using Nylon, most PVC,
Acetyl polymers like Delrin, as they are more hydroscopic and the
loss tangent causes some heating/softening. But they can be used FB
in low field applications such as at the low voltage end of circuits,
where RF current might be high.
These are modern engineered polymers and polymer/laminates, which I
have used or tested in very high power circuits from 27 to 200 MHz
over the past 20 years. Of course, the top material for low loss is
PTFE (Teflon) but it has poor mechanical properties as you know. Some
of the materials will carbon track if they arc over, and some don't.
As others have mentioned, the selection of a dielectric is dependent
on the voltage gradient, the frequency, the mechanical and thermal
properties, the ambient conditions, and in some cases, the dielectric
constant will play a significant role, so stability of that with
temperature is important.
At 7:09 PM -0400 7/12/06, amps-request@contesting.com wrote:
>Message: 4
>Date: Wed, 12 Jul 2006 17:28:22 -0400
>From: "Harold Mandel" <ka1xo@juno.com>
>Subject: Re: [Amps] Mica cap substitute \ alternative
>To: "'Gary Smith'" <wa6fgi@sbcglobal.net>, "'R L Measures'"
> <r@somis.org>, <g3rzp@g3rzp.wanadoo.co.uk>
>Cc: 'Amps Amps' <amps@contesting.com>
>Message-ID: <006901c6a5fa$1bc7be00$060ca8c0@laptopHM>
>Content-Type: text/plain; charset="us-ascii"
>
>Steatite, (porcelain); Corning Glass, PTFE....
>
>-----Original Message-----
>From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
>Behalf Of Gary Smith
>Sent: Wednesday, July 12, 2006 5:18 PM
>To: R L Measures; g3rzp@g3rzp.wanadoo.co.uk
>Cc: Amps Amps
>Subject: Re: [Amps] Mica cap substitute \ alternative
>
>At the risk of straying OT, what is a good insulator at 50 MHz or >?
>73,
>Gary...wa6fgi
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