In 1980, the first atomic clock was installed to regulate the carrier frequency. The current time signal is generated by extremely accurate caesium atomic clocks and phase-modulated on the 162 kHz carrier in a way that is inaudible when listening to the France Inter signal using a normal AM receivers. It requires a more complex receiver than the popular DCF77 service, but the much more powerful transmitter (22 to 40 times DCF77's 50 kW) gives it a much greater range of 3,500 km.