Its primary and backup transmitter are located at 50°0′56″N 9°00′39″E / 50.01556°N 9.01083°E / 50.01556; 9.01083 in Mainflingen, about 17 mi (27 km) south-east of Frankfurt am Main,[1] Germany.

DCF77 is controlled by the Physikalisch-Technische Bundesanstalt (PTB), Germany's national physics laboratory and transmits in continuous operation (24 hours).

It is operated by Media Broadcast GmbH (previously a subsidiary of Deutsche Telekom AG), 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.

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.

Since 2003, fourteen previously unused bits of the time code have been used for civil defence emergency signals.

As a further extension of the information content transmitted by DCF77, appropriately equipped radio clocks can provide a four-day weather forecast for 60 different regions in Europe.

[13][16] Since the bits previously reserved for the PTB are used, older radio clocks should not be affected by the weather data signal.

The signal distribution contract between the PTB and the DCF77 transmitter operator Media Broadcast GmbH is periodically renewed.

After negotiations in 2021, the PTB and Media Broadcast GmbH agreed to continue the dissemination of the German national legal time for the next 10 years.

In the past the PTB expressed it will initialize new negotiations if modernization activities at the transmitting station to improve the signal reception reliability throughout Europe are deemed necessary.

[17][18] The call sign DCF77 stands for D = Deutschland (Germany), C = long wave signal, F = Frankfurt am Main as the umbrella regional unit, 77 = frequency: 77.5 kHz.

[21] The chip sequence is generated by a 9-bit linear feedback shift register (LFSR), repeats every second, and begins with 00000100011000010011100101010110000….

Due to the GPS signal structure and the larger bandwidth available, the GPS reception would, in principle, achieve an uncertainty of the time transmission that is lower by at least one order of magnitude than the uncertainty that can be achieved with DCF77 phase modulation receiving hardware (GPS time is accurate to about ± 10 to 30 nanoseconds[22][23] and the Galileo April, May, June 2021 Quarterly Performance Report by the European GNSS Service Centre reported the UTC Time Dissemination Service Accuracy was ≤ 4.3 ns, computed by accumulating samples over the previous 12 months and exceeding the ≤ 30 ns target[24][25][26]).

With a relatively high power of 50 kW, the DCF77 transmissions can reliably be received in large parts of Europe, as far as 2,000 km (1,200 mi) from the transmitter in Mainflingen.

This is associated with a significant decrease in the signal strength and depends on many factors, e.g., the daytime and season, the angle of incidence of the skywave on the D-layer and the solar activity.

Via the public telephone network operational data of the control unit can be called up with the aid of a telecontrol system.

[36] The DCF77 transmitted carrier frequency relative uncertainty is 2 × 10−12 over a 24-hour period and 2 × 10−13 over 100 days, with a deviation in phase with respect to UTC that never exceeds 5.5 ± 0.3 microseconds.

[38] 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.

In theory, a DCF77 controlled external clock should be able to synchronize to within one half of the period of the transmitted 77.5 kHz carrier frequency of the DCF77 signal, or within ± 6.452 × 10−6 s or ± 6.452 microseconds.

[21] Due to the propagation process, phase and/or frequency shifts observed in received signals the practical obtainable accuracy is lower than originally realized with the atomic clocks at the place of transmission.

Such a small deviation will seldom be of interest and if desired instrument grade time receivers can be corrected for transit delay.

If pure ground wave reception is anticipated and the reception location is permanent a constant may be included in the calculation, while in the case of pure space waves the receiver cannot compensate for the fluctuations since these are the result of the changing altitude of the reflecting and bending layer of the ionosphere.

[33] Corrected instrument grade DCF77 receivers, using the amplitude-modulated time signals with accompanying antennas oriented tangential to the transmitter's antenna in Mainflingern to ensure the best possible interference-free time signal reception at fixed locations, can achieve a practical accuracy uncertainty better than ± 2 milliseconds.

[39] In addition to the amplitude-modulated time signal transmission this information is also transmitted since June 1983 by DCF77 via a phase modulation of the carrier wave with a pseudorandom noise sequence of 512 bits length.

[21] Normal low cost consumer grade DCF77 receivers solely rely on the amplitude-modulated time signals and use narrow band receivers (with 10 Hz bandwidth) with small ferrite loopstick antennas and circuits with non optimal digital signal processing delay and can therefore only be expected to determine the beginning of a second with a practical accuracy uncertainty of ± 0.1 second.