[time-nuts] RFDO - Experience and questions

paul swed paulswedb at gmail.com
Mon Mar 6 09:23:02 EST 2017


Gilles,
I just looked at the signal behavior from the TDFlink you sent.There are 14
seconds worth of very controlled phase. There are additional bits also.
As Bob says if the format is controlled you can predict the change and
correct the phase. This is exactly what I created for the wwvb BPSK signal
in the US about 1-2 years ago. It runs on a small arduino and requires no
modification to any of the phase tracking receivers. It super simple with
few parts. It was my first arduino project and took maybe a week of time at
night.

Granted I like the rest of the work you are doing and the prediction
concept can very reasonably be put into you software for prediction.
You should not need to worry about a unpredictable phase flip. On wwvb
there are a couple bits that can not be predicted but never seen that yet.
Even if they do a 3-4 second loop constant like all of the old receivers
has removes the issue.

Plan to warm up the HP3586 tonight and take a listen at 162 KHz in the US.
Regards
Paul
WB8TSL

On Mon, Mar 6, 2017 at 4:57 AM, Anders Wallin <anders.e.e.wallin at gmail.com>
wrote:

> FWIW, for fun I measured the LF stations MSF, DCF, and TDF just a few days
> ago. The signals look like this from our site:
> http://www.anderswallin.net/wp-content/uploads/2017/02/MSF.jpg
> http://www.anderswallin.net/wp-content/uploads/2017/02/DCF.jpg
> http://www.anderswallin.net/wp-content/uploads/2017/02/TDF.jpg
>
> I guess the +/- 40 Hz side-bands on TDF are by design?
>
> I have an SDR set up also, so the gnu-radio demodulators could run in
> parallel on each of these, and the sdr sampling clock could come from a
> local clock. One more project on the to-do list...
>
> Anders
>
>
> On Mon, Mar 6, 2017 at 12:42 AM, Iain Young <iain at g7iii.net> wrote:
>
> > On 05/03/17 20:23, paul swed wrote:
> >
> > Gilles what signal is that at 162KHz. A European station? Nice thats its
> C
> >> controlled.
> >>
> >
> > That's TDF from France. Their equivalent of WWV/MSF/DCF. Used to carry
> > the AM Station France Inter as well, but that went when France turned
> > off all LW, MW, and LORAN stations at the end of 2016.
> >
> > The Time Signal is Phase Modulated (I have a gnuradio decoder which
> > works very well if anyone is interested)
> >
> > See https://en.wikipedia.org/wiki/TDF_time_signal and
> > https://en.wikipedia.org/wiki/Allouis_longwave_transmitter
> >
> > With no AM modulation, there are obvious benefits with regards to using
> > it as a frequency reference. Average phase and frequency deviation is
> > zero over 200msec (see link above for details)
> >
> >
> > Iain
> >
> > PS, The signal is used by the French railways SNCF, the electricity
> > distributor ENEDIS, airports, hospitals according to the Allouis link
> > above
> >
> >
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