[time-nuts] WWV receivers?

Attila Kinali attila at kinali.ch
Sat Oct 29 15:07:18 EDT 2016

On Sat, 29 Oct 2016 09:35:25 -0700
jimlux <jimlux at earthlink.net> wrote:

> > Should not be too high. If Jeff Sherman's and Robert Jörden's paper[1]
> > is any indication, then the jitter should be dominated by the jitter
> > of the ADC and its reference oscillator. So sub-ps, order of 100fs jitter
> > should be possible with proper design. Long term drift is another issue
> > and I have not completely figured out what are the contributors there.
> > Temperature stabilizing for sure helps, but it doesn't seem to be the
> > only effect.
> Well, that's "jitter in the original samples" which can be very low, as 
> you describe. But I would interpret the original question as "jitter 
> *through* an SDR" which implies that we're looking at the timing of 
> output vs input.

Oh.. yes...The whole latency into the PC is a whole different game.
I don't know the numbers for SDR, but for soundcards that delay jitter
is usually in the couple 100µs range, Ie way lower than most people
would notice. But this is only true if the OS reports the buffer sizes
correctly. On Linux that means no pulseaudio as it is known to mess up
the buffer reporting completely, to the point where it was off by 10's of ms.

I don't know what the numbers under windows are, but as I have never heard
of any problems there it might just work correctly out of the box.

Those I know who do precsision timing with SDR usually use the timestamping
facilities on the SDR hardware and process those timestamps within GnuRadio.

				Attila Kinali
Malek's Law:
        Any simple idea will be worded in the most complicated way.

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