[time-nuts] DAC performance [WAS: Papers on timing for lunar laser ranging]
kb8tq at n1k.org
Sun Jul 16 21:49:07 EDT 2017
This is a limitation on an OCXO based GPSDO. That’s really the bottom line here.
It’s a limitation in an OCXO based part, but not in one based on an Rb or a Cs. If
the added component costs far more than a Cs, it’s not an answer.
> On Jul 16, 2017, at 7:25 PM, Chris Albertson <albertson.chris at gmail.com> wrote:
> What about josephson standards? After all, this is "Time Nuts" and we are
> allowed to propose silly-complex solutions to simple problems if it
> improves performance even a little.
> But seriously I thought the issue of making a perfect voltage standard was
> solved because the Volt is defined to be whatever the Josephson array
> produces. Yes expensive because to runs at nearly absolute zero.
> On Sun, Jul 16, 2017 at 4:10 PM, Bob kb8tq <kb8tq at n1k.org> wrote:
>>> On Jul 16, 2017, at 6:33 PM, Richard (Rick) Karlquist <
>> richard at karlquist.com> wrote:
>>> On 7/16/2017 1:51 PM, Bob kb8tq wrote:
>>>> One gotcha with any ADC or DAC is going to be the reference. There, you
>> are in the same
>>>> “get what you pay for” dilemma. Stable and noisy, can do. Quiet and not
>> very stable, can do.
>>>> Both stable and quiet, not so easy if you want it cheap.
>>>> Noise can also be the sigma delta ADC’s weak point. Even at slow rates,
>> some of them need
>>>> a lot of averages to quiet down.
>>> The reference initially used in the E1938A turned out to be too
>> noisy/unstable. It was non trivial to find an upgrade. The
>>> HP Smart Clocks of 20 years ago were limited in their performance
>>> by the reference used.
>>> Has there been much improvement in references in the intervening
>>> 20 years?
>> They still don’t seem to have the hysteresis problem licked. Yes, you can
>> do an oversized reference
>> and take care of the issue. More or less that’s what you would have done
>> 20 years ago.
>>> Rick N6RK
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> Chris Albertson
> Redondo Beach, California
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