Radio 4 is particularly interesting, as it carries additional 25bps data [0] using for radio teleswitch operation [1] - a service whose days are numbered. Quite

Radio 4 is particularly interesting, as it carries additional 25bps data [0] using for radio teleswitch operation [1] - a service whose days are numbered. Quite fun to receive this signal, as it's trivial to build a 198KHz receiver and to recover the data stream (+ time signal) using a signal, e.g. mix it with a 200KHz signal and process the resultant 2Khz audio tone. [0] https://www.bbc.co.uk/rd/publications/rdreport_1984_19 https://www.bbc.co.uk/rd/publications/rdreport_1984_19 [1] https://en.wikipedia.org/wiki/Radio_teleswitch https://en.wikipedia.org/wiki/Radio_teleswitch