[time-nuts] DMTD was: high rev isolation amps

Bob Stewart bob at evoria.net
Wed May 11 20:24:04 EDT 2016


Hi Bob et al,

I'm finally drawing up a schematic for a DMTD and I thought I'd use the NBS circuits for a lot of it.  So, how about PZT3904 transistors in the isolation amps?  They're in SOT-223 with the heat sink tab.

I figure to use some version of the TUF-1 for the DBMs.  The first version will be a bit breadboardish.  I'll use the PRS-45A as the reference oscillator and the 8640B as the offset oscillator.  If it's workable, then I thought I'd put an Analog Devices DDS onboard with a small PIC to set it up.  I haven't gotten as far as the zero-crossing detectors yet, but I was thinking of using 125 gates.

Bob
--------------------------------------------
On Tue, 3/29/16, Bob Camp <kb8tq at n1k.org> wrote:

 Subject: Re: [time-nuts] high rev isolation amps
 To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
 Date: Tuesday, March 29, 2016, 6:08 PM
 
 Hi
 
 There were (and maybe still are) SOT-89 versions of the
 2N3804 and 3906. They will handle more
 power than most of the other versions. That gives you better
 Vce on the string. They also have less
 package inductance which helps tie the base to ground. If
 you are building some of those circuits, they
 are worth looking for.
 
 Bob
 
 > On Mar 29, 2016, at 6:47 AM, Charles Steinmetz <csteinmetz at yandex.com>
 wrote:
 > 
 > See below for schematics of the NIST isolation
 amplifiers from 1990 and 1997.  NIST reported the
 isolation as >120dB.
 > 
 > I built isolation amplifiers similar to these (with
 lower-noise power supplies and biasing tinkered slightly for
 better dynamic range), and with careful construction
 achieved isolation substantially better than 120dB (see my
 post of 11/25/14 for more details).
 > 
 > Best regards,
 > 
 > Charles
 >
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