[time-nuts] WWV receivers?

[Chris Albertson]

There is zero jitter through the SDR software because you can always buffer
the output and then reclock it on output and all you have to deal with is a
known fixed delay.  If the samples are clocked in accurately that is all
you need.

Some audio interfaces have can have very good timing and run off an
external reference oscillator.  But those are typically found in
professional studios.  (Some studios have coax or fiber frequency
distribution.) But The typical home studio audio interface that sells for
under $200 uses a four pin  oscillator.

The bigger question is propagation.



On Sat, Oct 29, 2016 at 12:07 PM, Attila Kinali <attila at kinali.ch> wrote:

> 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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-- 

Chris Albertson
Redondo Beach, California