[time-nuts] DAC performance [WAS: Papers on timing for lunar laser ranging]
albertson.chris at gmail.com
Sun Jul 16 19:25:21 EDT 2017
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:
> >> Hi
> >> 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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Redondo Beach, California
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