HBG (time signal)
The time transmitter HBG was a time transmission service by the Federal Office of Metrology ( METAS) in Switzerland.
This long wave transmitter on Lake Geneva beamed from the statutory Swiss time (Central European Time CET or Central European Summer Time CEST ) and was used for synchronization of radio clocks. The name HBG is the call sign of the station.
The format ( HBG code) of the broadcast time signal was compatible with the German DCF77 since 1 January 2001. Previously, minor differences such as the second 59 were present. The commercially available receiver modules were mostly able to both old as well as to decode the new code.
HBG sent in 24- hour operation. The broadcast time signal could be used without restriction and free of charge.
The station was commissioned in 1966 Prangins on Lake Geneva in operation. The carrier frequency was 75 kHz ( long wave) and is emitted with a transmission power of 25 kW on a omnidirectional antenna.
The antenna system was a T- antenna, built in 1928 between two free-standing steel lattice towers was excited with 125 m height was used. Both towers were grounded, and possessed at the bottom by an expansion of 10 x 10 meters. The range of the ground wave was about 500 miles and cover the whole of Switzerland and parts of neighboring countries. In this area a perfect reception was guaranteed, even inside buildings and in most cases even in the basement. In the area of 500 km to 1000 km of reception could be impaired by interference with the space wave (fading), from 1000 km then outweighed the space wave.
Establishments was the first FM station of the PTT, then until May 2000 from Swisscom and finally by the Federal Office of Metrology ( METAS). In August 2009 it was announced that the station would cease with the end of 2011 the operation. The antenna masts had aging phenomena which constitute a safety hazard and their elimination would have been possible only with considerable effort. The two towers were demolished by controlled demolition on September 6, 2012 at 14:00 local time.
Time and Frequency
The Federal Office of Metrology ( METAS) has the statutory duty to provide the basic units of measurement are available, including the second according to the International System of Units SI. To this end, the laboratory for time and frequency of the Federal Office operates several atomic clocks that act as frequency and time standards. From these atomic clocks, the Swiss statutory time is calculated.
The transmitter HBG transmitted not only the Swiss time, but also a very accurate frequency: The carrier frequency of the transmitter is also derived from these atomic clocks, could therefore be maintained at 75 kHz within -12 2:10 and was thus a calibration frequency.
Format of the time signal
At the beginning of every second of the carrier signal was briefly interrupted ( amplitude shift keying ). This second pulse was missing in the last second of each minute (ie, in seconds 59) to signal the beginning of a new minute. For this was sent a double pulse in the first second of the new Minute ( 0 seconds ). A triple pulse instead of the double pulse marked the beginning of a new hour, a four -pulse the beginning of a new day.
At irregular intervals, a leap second had to be pushed to the Coordinated Universal Time UTC again ( dependent on the Earth's rotation ) to approximate Universal Time UT1. In these cases the data was minute 61 seconds long, the leap second was added at the end ( as a second 60) and also did not receive a second pulse.
In the second pulses additional details were coded to Date and Time: Short second pulses of 100 ms duration meant a binary 0, longer second pulses of 200 ms duration, a binary 1 (pulse width modulation). In this way, 59 -bit information could be transmitted in every minute. The exact structure of this one-minute data message is contained in the accompanying table.
The transmitted information can be divided into several classes:
- Advance Notice: These bits are set 12 hours before the event (ie insertion of a leap second, or change of time zone between GMT and EDT ) and will be deleted immediately after the event again.
- Figures: in BCD format, sent with the least significant bit first ( little endian format). The received bits with the weights 1, 2, 4, 8, 10, 20, 40, 80 For each number were planned only as many bits as the range of values required, for example 7 bits for the minute (range 0 to 59) but only 6 bits for the hour ( range 0 to 23).
- Weekday: The received number was interpreted in accordance with ISO 8601: 1 = Monday, 2 = Tuesday to 7 = Sunday
- Parity bit: The parity bits complemented the sum of the specified data bits to an even number ( even parity) and served the fault detection.