Logo PTB
View of the Mainflingen long-wave radio station for transmission of the DCF77 signal: transmitter building (in the back), antenna building (yellow bricks) and antenna masts.

Frequency transfer using Loran and TV signals

Img.: LORAN signal of the Sylt transmitter

In the past, time and frequency transmission via LORAN and via synchronization pulses in television signals played an important part. The first-mentioned became ever less important with the appearance of GPS so that PTB does not publish the arrival times of the signals of the LORAN Sylt transmitter received in Braunschweig regularly any longer. The values can be obtained on request. The LORAN transmitters in Europe and USA continue, however, to be operated and are even extended as “back-up“ for satellite-supported navigation systems. Information on this can be found under www.loran.org and www.nels.org.

For many years, in particular after the German Unification, frequency comparisons with UTC(PTB) via the image synchronization pulses in the TV signals of the ZDF (Second German Television Channel) have been important to maintain the industry’s measurement infrastructure in the new federal states. In the technical centre of the ZDF, the colour carrier and the synchronous pulses contained in the television signal have been (and still are) de-rived from a rubidium frequency standard whose output frequency has been controlled by comparison with the received DCF77 carrier frequency - with the frequency of UTC(PTB) with a relative uncertainty of less than 1.10-11. As a result of the current practice of digital transmission of the TV signal between individual production sites, the central transmitting studio and the partially digital emission, the propagation times on these transmission paths no longer show constant values or only monotonously changing ones. This is why the procedure of the TV frequency comparisons can be made use of only temporarily and regionally and will therefore probably become less important. PTB will no longer provide any relevant data.

The digital terrestrial television reception which is gradually being extended in Germany, does not even allow the correct time to be transmitted to the spectators: The television pictures are displayed the TV on the screen with a delay of up to several seconds.