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DCF77 suitable for public warnings

So far, in the first fourteen seconds of each minute, the DCF77 time signal transmitter has broadcast only status information and no time code. On behalf of the Federal Ministry of the Interior it has been investigated whether warnings to the general public could be transmitted instead in hazardous situations. The final report now available favours such an extended use of the time signal transmitter.

The Bundesamt für Bevölkerungsschutz und Katastrophenhilfe (BBK, Federal Office for Civil Defense and Disaster Relief) in the sphere of business of the Federal Ministry of the Interior is looking for an alternative to the siren systems which are practically no longer available, to alert the population in cases of crises or catastrophes via a “reveille”. HKW Elektronik GmbH was commissioned to perform and evaluate a field test. For this purpose, the DCF77 long-wave transmitter was integrated into the SatWas satellite warning system of the Federal Government, to emit (initially fictive) warning information in the second marks 1 to 14.

Between October 13 and December 10, 2003, a total of 39 test alarms were emitted which were to be registered by 1000 receivers distributed all over the country. Additional silent alarms could only be registered by 50 industrial radio controlled clocks. The alarm protocols covered 3 · 14 bits and were emitted in 3 successive minutes. The clocks used were modified, commercially available radio controlled clocks (wrist watches, alarm clocks, wall clocks, PC radio controlled clocks) which, in addition to their standard functionality, were equipped with optical and acoustic alarms. The participants in the field test had committed themselves to report the alarms (also false alarms) via the Internet.

In its final report, HKW now informs that alarming time and the availability of SatWas information are consistently good all over Germany. The environment (countryside vs. congested urban areas, indoors vs. outdoors) and the distance to the emitter had only little influence on the reception probability. However, it turned out that the location selected for stationary clocks and the wearing habit for wristwatches exerted a considerable influence. The number of false alarms was negligibly small.

The results of this field test are also of interest to PTB, as this test offered the rare possibility to systematically investigate the reception conditions for information encoded in the DCF77 signal. The results confirms the assessments PTB made through many years of contact with developers and owners of radio controlled clocks: Malfunctions of the clocks are almost exclusively due to individual handling errors by users.

Now, based on the final report the Federal Ministry of the Interior must decide whether DCF77 will become part of the overall system for public warnings in the long run. The positive results suggest this.

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