I am working on another clock, this time with MSF (Rugby/The time from NPL) radio time setting. I know, I need to document the last one… Anyway, I finished the decoder today.
The MSF signal is frankly a mess. Things seem to have been added and then removed over the years. There are four different length pulses and various additions. Compared to the nice clean DCF77 signal it’s horrible, but unfortunately I can’t get DCF77 to work reliably here. In fact I bought a DCF77 clock but it has never been able to receive a good enough signal to set itself.
As others have discovered the MSF signal is much cleaner at night, but filtering out the noise during the day isn’t too hard. I wrote the decoder in assembler and it basically waits for a valid bit and then locks on to that, ignoring everything until 950ms have passed from it’s start. It also filters out too short and too long pulses and does some debouncing.