GM Bruce. I found some basic information on TDF on the net. In short it is phase modulation. Here are some more details:The French LF time station TDF (Allouis 162 kHz, now often referred to as ALS162) utilizes Phase Modulation (PM) to transmit digital time data. It specifically employs a phase shift of +/- 1 radian over a 0.1-second interval every second (except the 59th) to encode binary data, with a doubled modulation pattern representing a binary 1.
Key Details of TDF (ALS162) Modulation: Carrier Frequency: 162 kHz. Modulation Type: Phase Modulation (PM) of the carrier. Data Encoding: A 0.1s phase shift (+/- 1 rad) occurs every second. Binary 0: A single 0.1s phase modulation. Binary 1: The modulation is repeated (or doubled).
Structure: Similar to the DCF77 signal, it transmits time and date information from the 21st to the 58th second of each minute. Signal State: While it was formerly transmitted alongside the France Inter AM radio signal, the 162 kHz carrier remains active specifically for this digital time signal.