page_title: DCF77
section_title: Control
hierarchical_section_title: DCF77 / Control
caption_attribution_description: English: Atomic clock CS2 at the Physikalisch Technischen Bundesanstalt, Braunschweig. CS2 provides the German national legal time standard. Open house day 1997. Deutsch: Atomuhr CS-2 der Physikalisch Technischen Bundesanstalt Braunschweig. Tag der offenen Tür 1997.
context_page_description: DCF77 is a German longwave time signal and standard-frequency radio station. It started service as a standard-frequency station on 1 January 1959. In June 1973 date and time information was added. Its primary and backup transmitter are located at 50°0′56″N 9°00′39″E in Mainflingen, about 25 km south-east of Frankfurt am Main, Germany. The transmitter generates a nominal power of 50 kW, of which about 30 to 35 kW can be radiated via a T-antenna.
  DCF77 is controlled by the Physikalisch-Technische Bundesanstalt, Germany's national physics laboratory and transmits in continuous operation. It is operated by Media Broadcast GmbH, on behalf of the PTB. With Media Broadcast GmbH, a temporal transmission availability of at least 99.7% per year or under 26.28 hours of annual downtime has been agreed upon. Most service interruptions are short-term disconnections of under two minutes. Longer lasting transmission service interruptions are generally caused by strong winds, freezing rain or snow induced T-antenna movement. This manifests itself in electrical detuning of the antenna resonance circuit and hence a measurable phase modulation of the received signal.
context_section_description: 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 an air conditioned room of the transmitting station, is shielded against high-frequency interferences and controlled from Braunschweig. For reasons of operational reliability, the control signal is generated by three independent control channels all equipped with their own caesium atomic clock. In addition a rubidium atomic clock is available on site. To avoid incorrect emissions the output of these three channels are compared in two electronic switch circuits on site. Output for transmission is only generated when at least two of the three channels are in agreement. 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 master clocks that provide the UTC (PTB). 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.
caption: Atomic master clock CS2 in use at the PTB to check for deviations
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