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StructureDiv. 4 Optics4.4 Time and Frequency4.42 Dissemination of TimeDissemination of legal timeDCF77 > DCF77 carrier frequency
DCF77 carrier frequency

Atomic clocks whose output signal (5 or 10 MHz) is used to generate the DCF77 carrier oscillation of 77.5 kHz and the time code (left: GPS disciplined Rubidium atomic frequency standard, middle and right: caesium atomic clocks).

The carrier frequency of DCF77 is 77.5 kHz. It is derived from an atomic clock of PTB and deviates at the place of transmission on average by less than relatively 2 · 10-12 on one day, and on average by less than relatively 2 · 10-13 during 100 days from the nominal value. The uncertainty stated corresponds to the expanded uncertainty (k=2) in accordance with a confidence interval of 95%. The phase time of the carrier – in other words: zero crossing of the 77.5 kHz carrier oscillation received at PTB with a period of 12.9 µs which follows the second start according to UTC(PTB) – is maintained within an arbitrarily selected phase time deviation of (5.5 ± 0.3) µs in agreement with UTC(PTB). For this purpose, the phase of the received signal is compared in Braunschweig with the aid of two special DCF77 receivers with second impulses according to UTC(PTB) and with a 77.5 kHz pulse sequence derived from UTC(PTB). Due to the propagation process, phase and/or frequency shifts observed in received signals is larger than originally realized with the atomic clocks at the place of transmission.


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