Pragotron Slave Clock – Part 3 – Software

My previous experiments around decoding long wave radio time signals primarily involved using the UK’s time signal MSF60 (https://en.wikipedia.org/wiki/Time_from_NPL) previously known as the Rugby time signal. This transmission no longer originates from Rugby, it moved north to cumbria and seems to have reduced power during the move, combined with the fact the the 60kHz signal seems to be drowned out by RF interference from my computer equipment made me look at alternatives.

Whilst looking around I stumbled across some work by Udo Klein (https://blog.blinkenlight.net/experiments/dcf77/dcf77-library/). Udo recognised the fact that interference to these signals was a big problem and wrote a library that would effectively use some digital signal processing techniques to improve the receivers immunity to noise.  Clearly where the signal is drowned out by computer RF interference all bets will be off but in locations where there is mostly a good chance of reception the algorithm does allow much noise to be ignored and lead to time recovery.

I extended this library for MSF and Udo has since merged these changes into the repository so you can try it out for yourself and see how you get on.  The performance seems a lot better than just using averaging and copes well with transients of noise.  Be aware however that correct positioning and orientation of the radio clock module is still vital, you need to experiment and should get flashes around 1 or 2Hz, crazy flashing probably means you are picking up your computer RFI rather than the time signal.

I have a collection of MSF and DCF modules now, either would work but for this project I decided to go with the last one I had connected so I am receiving the time signal from DCF77 (https://en.wikipedia.org/wiki/DCF77).

It seems that summer time for DCF77 now occurs at the same time that UK time changes it’s daylight savings (EU good for standard harmonisation, not so good for uncontrolled migration, un-democratic super-state etc, bring on June 23rd!) so the clock simply has to maintain a fixed offset and the daylight savings should work OK.

Most of the hardwork is done by Udo’s library but the extra code and a copy of the DCF77 decoder is here (https://gitlab.com/NivagSwerdna/SlaveClockDriver).

And it works!

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About nivagswerdna

Professional Geek
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