[Amps] dielectrics TSPA

[John T. M. Lyles]

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 at contesting.com wrote:
>Message: 4
>Date: Wed, 12 Jul 2006 17:28:22 -0400
>From: "Harold  Mandel" <ka1xo at juno.com>
>Subject: Re: [Amps] Mica cap substitute \ alternative
>To: "'Gary Smith'" <wa6fgi at sbcglobal.net>,	"'R L Measures'"
>	<r at somis.org>, <g3rzp at g3rzp.wanadoo.co.uk>
>Cc: 'Amps Amps' <amps at contesting.com>
>Message-ID: <006901c6a5fa$1bc7be00$060ca8c0 at laptopHM>
>Content-Type: text/plain;	charset="us-ascii"
>
>Steatite, (porcelain); Corning Glass, PTFE....
>
>-----Original Message-----
>From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
>Behalf Of Gary Smith
>Sent: Wednesday, July 12, 2006 5:18 PM
>To: R L Measures; g3rzp at 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