[time-nuts] DMTD was: high rev isolation amps
Bob Stewart
bob at evoria.net
Wed May 11 23:44:11 EDT 2016
Hi Bruce,
I was thinking of using the 125s as the zero crossing detectors.
Won't the DDS spurs cancel out across the 2 DBMS?
Bob
--------------------------------------------
On Wed, 5/11/16, Bruce Griffiths <bruce.griffiths at xtra.co.nz> wrote:
Subject: Re: [time-nuts] DMTD was: high rev isolation amps
To: "Bob Stewart" <bob at evoria.net>, "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
Date: Wednesday, May 11, 2016, 10:33 PM
For
DMTD service with an offset frequency of 100Hz or less the
flicker phase noise of the mixer is more important than its
wideband PN floor.The
RDP series phase detectors are amongst the lowest PN noise
mixer/phase detectors commercially available. They are
considerably quieter than the TUF series mixers.To
minimise noise both the RF and LO ports should be
saturated.The
specified IF port termination at the sum frequenncy should
be used to avoid degrading the isolation between the RF
and LO ports.
For
even lower flicker noise using a mixer assembled using
2N2222A's as diodes is even quieter as NIST have
shown.
125
gates have large flicker noise and using these in the front
end of the zero crossing detector will increase the noise
substantially over that obtainable with a well designed zero
crossing amplifier chain using opamps.Using
a DDS to generate the offset frequency raises the ugly
sepctre of unwanted close in
spurs, unless one chooses one of the magic frequency outputs
that is free of such spurs.
Bruce
On Thursday, 12 May
2016 3:00 PM, Bob Stewart <bob at evoria.net> wrote:
Hi
Bob,
OK, I can see that.
I had been wondering about how to build it out, but it seems
like each module should be on its own PCB for isolation.
That keeps the costs down, except for the numerous SMA
jumpers - and the eventual big box.
Bob
--------------------------------------------
On Wed, 5/11/16, Bob Camp <kb8tq at n1k.org>
wrote:
Subject: Re:
[time-nuts] DMTD was: high rev isolation amps
To: "Bob Stewart" <bob at evoria.net>,
"Discussion of precise time and frequency
measurement" <time-nuts at febo.com>
Date: Wednesday, May 11, 2016, 8:44 PM
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>_______________________________________________
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>
>
_______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
_______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
_______________________________________________
time-nuts mailing list -- time-nuts at febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
More information about the time-nuts
mailing list