[time-nuts] RFDO - Experience and questions

Bob Camp kb8tq at n1k.org
Mon Mar 6 02:26:17 EST 2017


One way to “cheat” at recovering a time signal is to demodulate it with
known information. Once you know the information from the first “frame”
of data (time, date, etc) you can predict what the information in the next
frame will be. Yes it does take a little work. If the signal is completely defined 
(no extra data about the weather forecast or something like that) you can
reduce your bandwidth significantly.


> On Mar 5, 2017, at 11:42 PM, 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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