[time-nuts] Receiving the MSF time signal on cheap radio modules

Deirdre O'Byrne deirdre.dub at gmail.com
Tue Feb 6 15:48:41 EST 2018


Thanks for the feedback!

On 6 February 2018 at 20:29, Tom Van Baak <tvb at leapsecond.com> wrote:

> 2) Not all decoding errors are equal. Since this is a time code instead of
> arbitrary binary data you can use the internal structure of the data to
> your benefit.

As I said to Poul-Henning, that is the next level of error detection, which
also has application in error correcting some of the "almost-right" signals.

> 3) A side-effect of your data set is that you can track performance of the
> oscillator inside the logic analyzer: convert the 700k GPS timestamps into
> interval, find and replace the 4 glitch lines with 2 lines of 1.000150, and
> then use Stable32 or TimeLab to plot. I used a 10 minute running average to
> reduce the 50 us quantization noise. Note the mean frequency of your
> timebase is 152 ppm low.

I made it out to be 152.2ppm, which is kinda disappointing. But the signal
analyser cost very little, and you get what you pay for.

I have not yet wrapped my head around how to create ADEV plots, so thanks
for your work on that - it's interesting to see that (presumed) initial
thermal effect.

> Over 8 days this results in a cumulative sampling error of 105 seconds. If
> your decoding algorithms are relative instead of absolute this won't be a
> problem. OTOH, you may be able to use your decoding process to detect this
> drift and then compensate for it in software. You have the beginnings of a
> MSF-Disciplined-Oscillator project.

MSF disciplined oscillator?! I don't trust these receivers to any better
than about the 20ms mark, so such a disciplined oscillator would have quite
a long integration time!

Thanks again.

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