Re: Beating Solved

To: tesla-at-pupman-dot-com
Subject: Re: Beating Solved
From: Richard Hull <hullr-at-whitlock-dot-com>
Date: Mon, 09 Sep 1996 16:02:39 -0700
Tesla List wrote:
> 
> >From ed-at-alumni.caltech.eduSat Sep  7 15:26:33 1996
> Date: Fri, 6 Sep 1996 19:55:09 -0700 (PDT)
> From: "Edward V. Phillips" <ed-at-alumni.caltech.edu>
> To: tesla-at-pupman-dot-com
> Subject: Re: Beating Solved
> 
> Re: Mica losses
>         Good EXTENDED FOIL mica capacitors can have Q's of well
> over 1000 at 1 MHz.  Not sure where your loss data came from, but
> doesn't sound right to me.  My copy (4th edition here at home) of the
> ITT Reference Data for Radio Engineers gives the dissipation factor
> of ruby mica as 0.0006 at 1 kHz, and 0.0003 at 1 MHz.  I have used
> lots of silvered mica (should have same loss) in filter applications
> where, for all practical purposes, they performed as if lossless.
> Ed


Ed, 

 The RF grade ruby muscovite mica to which you refer comes from Bengal 
India.  It is a special type and form of Mica and is virtually losseless, 
but is not available for big (tesla grade micas).  I have two contacts at 
major mica firms and I have them casting about for a series of 2" by 2" 
mica sheets of this ultra good mica.  Most of it is "mined out"!!  The 
biggest books now produce no more than 1" square skives of it.  Its is 
still used in the silver micas 1/4"X1/2" plates.  These are for precision 
Rf circuitry and are in no danger of disappearing.  All modern larger 
micas come from a more common US form found in and around Feldspar mines. 
 This material is available in up to 6 inch square sheets but itself is 
becoming rare!  The bulk of mica caps made of any size are from 
reconstituted mica and are very lossey.  NWL bought the last US producer 
of Mica caps and I talked at length with one of their engineers and he 
assured me that the old days of high value micas for losseless RF use are 
over!  As much from the outrageous prices per unit as from rarity of good 
ruby muscovite mica.

The mica I used for my tests, was the V2 grade pure capacitor mica (not 
reconstituted)  I obtained 50 sheets of 4"X6" mica for $300.00 in 1992.  
It is beautiful, like glass, .005 thick.  The stuff was lossey .02 - 2% -at- 
500khz.  I can no longer obtain even this material!  I am told only 2"X4" 
sheets of this good American material is to be had.

Richard Hull, TCBOR