Receiving the MSF time signal on cheap radio modules
Hi
Back in the era of VLF disciplined oscillators, carrier phase was the preferred approach.
Getting that to work with 100% AM modulation took some effort ….
Bob
On Feb 7, 2018, at 2:13 AM, Poul-Henning Kamp phk@phk.freebsd.dk wrote:
In message CAGJ4F+697SyXwm3yWG-XczN4zF7r2RAmXzAcEm=dhaqBJc_NNw@mail.gmail.com, "Deirdre O'Byrne" writes:
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!
It's actually more complicated and better than that.
The low-pass filter dominates, so the falling flank at second N
depends on the pulsewidth at second N-1.
I can't remember the numbers I got when I "sorted" DCF77 pulses depending
on the previous pulse being short or long, but it was a fair bit better
than 20ms.
--
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No doubt! But I'm trying to remain as inexpensive as possible.
That it might be possie to get 5ms (300 carrier periods!) from an
off-the-shelf consumer-grade component not designed for accuracy is pretty
cool IMO.
On 7 Feb 2018 14:31, "Bob kb8tq" kb8tq@n1k.org wrote:
Hi
Back in the era of VLF disciplined oscillators, carrier phase was the
preferred approach.
Getting that to work with 100% AM modulation took some effort ….
Bob
On Feb 7, 2018, at 2:13 AM, Poul-Henning Kamp phk@phk.freebsd.dk wrote:
In message <CAGJ4F+697SyXwm3yWG-XczN4zF7r2RAmXzAcEm=dhaqBJc_
NNw@mail.gmail.com>, "Deirdre O'Byrne" writes:
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!
It's actually more complicated and better than that.
The low-pass filter dominates, so the falling flank at second N
depends on the pulsewidth at second N-1.
I can't remember the numbers I got when I "sorted" DCF77 pulses depending
on the previous pulse being short or long, but it was a fair bit better
than 20ms.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@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.
mailman/listinfo/time-nuts
and follow the instructions there.
In message CAGJ4F+6jBu6T0RVfdf5Z4gfmV6NYkNKGZM9q0MHjLZb60MKOLA@mail.gmail.com, "Deirdre O'Byrne" writes:
I've updated my paper, which now contains the attached graph. (I did a
linear regression analysis to see what the correction for the receivers
should be, and I applied receiver 2's correction to both receivers to
generate this graph).
Yes, these cheap "clock-receivers" vary a lot and they are usually also
very temperature sensitive.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@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.
On 07/02/18 01:16, Bob kb8tq wrote:
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!
Once upon a time, that was how people did disciplined oscillators. Part of the
answer to “how?” is that their target accuracies were not as tight as what we now
think of as normal.
I was under the impression the Radio Four carrier (198kHz ex 200kHz) was
the old "frequency standard of choice" in the UK, prior to GPS.
I don't recall anyone using MSF for much other than "what time is it, to
maybe the nearest second?".
Though I do recall John Becker of EPE magazine did a nifty little
millennium countdown clock using MSF as a base.