[time-nuts] Re: function generator

[Jeremy Elson]

I did not see any such setting in the Rigol, but I'll check again. in April
I did write to Rigol to report the problem and had the following (abridged)
conversation with support:

Me:

"I recently tried to use your DG1022Z signal generator to generate one
pulse-per-second (pulse mode, frequency 1.000000hz, width 10 microseconds).
However, it appears there is a small frequency error of one part in 1e11,
i.e. the pulse per second gets later by about 6 nanoseconds every 1,000
seconds." [More technical description abridged, including a link to a
graph.]

Rigol:

"Please find the following datasheet for DG1000Z, the accuracy is +/-1ppm.
If your pulse is 1second with 10us width, 6ns per 1000s is in the accuracy
range."  [They attached an image of a page from the DG1000Z datasheet,
showing a line that said "Accuracy: +/- 1ppm of the setting value"]

Me:

"Is this the specification even when the unit is provided with an accurate
external clock?"

Rigol:

"I would say Yes. The internal processing circuit will effect the clock
signal,  harmonics and phase noise will result the frequency variance."

-Jeremy

On Sun, Nov 21, 2021 at 11:54 PM Poul-Henning Kamp <phk at phk.freebsd.dk>
wrote:

> --------
> Jeremy Elson writes:
>
> > [...] I plugged an RbXO into the DG1022Z and simply asked the
> > DG1022Z to divide it down to a 1pps signal. That is, I configured it to
> > create a pulse with a small duty cycle and 1hz frequency using the
> external
> > clock as a reference. To my surprise, it introduces a small but
> > measurable error of one part in 1E11 in the dividing-down. You can read
> the
> > full story of this in my post from earlier this year:
>
> When you feed such instruments an external clock, you often have to change
> one or more calibration constants for the internal (OC)XO's offset to zero.
>
> Another problem is that if you use the square wave output of a DDS based
> generator, they often produce the square from the sine output of
> the DDS chip with a schmitt-trigger, which causes lousy jitter.
>
> --
> Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
> phk at FreeBSD.ORG         | TCP/IP since RFC 956
> FreeBSD committer       | BSD since 4.3-tahoe
> Never attribute to malice what can adequately be explained by incompetence.
>