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

Bob Camp kb8tq at n1k.org
Thu May 12 01:44:17 UTC 2016


Hi

For extra added “Time Nut” grade fun:

Clip the collector lead off of the SOT-223 packages (between emitter and base leads). You probably will gain a couple of db of isolation. (running common base).

Bob

> On May 11, 2016, at 8:24 PM, Bob Stewart <bob at evoria.net> wrote:
> 
> 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
>> 
> <NIST_120dB_isolation_amplifier_schematic_email.gif><Iso_amp_NIST_schematic_with_values_5MHz_1997_email.gif>_______________________________________________
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