DCF77 - Control

Control

The control signal is not transmitted by wire from the Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig to the transmitting radio station in Mainflingen but is generated at the place of emission using a control unit developed by the PTB. This control unit, which is housed in a room of the transmitting station, is shielded against high-frequency interferences and controlled from Braunschweig. Via the public telephone network operational data of the control unit can be called up with the aid of a telecontrol system. Furthermore, the carrier phase time and the states of the second markers are compared in Braunschweig with the setpoints specified by the PTB's atomic clocks. Of these atomic clocks the CS2 atomic clock in Braunschweig provides the German national legal time standard, and can be used as a highly accurate frequency standard. If there are deviations, the necessary corrections will be made via the telecontrol system.

The DCF77 transmitted carrier frequency relative uncertainty is 2 x 10-12 over a 24-hour period and 2 x 10-13 over 100 days, with a deviation in phase with respect to UTC that never exceeds more than 5.5 ± 0.3 microseconds. The four German caesium atomic clocks (CS1, CS2, CSF1 and CSF2) used by PTB in Braunschweig ensure significantly less long term clock drift than the atomic clocks used in the DCF77 facility in Mainflingen. With the aid of external corrections from Braunschweig the control unit of DCF77 in Mainflingen is expected to neither gain nor lose a second in approximately 300,000 years.