GB1518892A - Time signal receiver - Google Patents

Abstract

1518892 Standard time-code receiver clock EUROPEAN ELECTRONIC SYSTEMS Ltd 26 Jan 1977 [26 Jan 1976] 02941/76 Heading G3T A time signal receiver is constructed to detect, interpret and display a Greenwich Mean Time signal derived from an atomic clock and transmitted by radio wave from Rugby. The signal, Fig. 1, comprises an amplitude modulated 60KHZ carrier wave comprising bursts 11, the trailing edge of each burst demareating each second. Between the end of one minute and the beginning of the next, is a period of 500 msecs containing a code indicating correct G.M.T. as detailed Fig. 2. The code includes a control pulse 21, a marker pulse 23 and a 140 msecs block containing 14 bits indicating tens of hours, hours, tens of minutes, minutes. In order to detect consistently the beginning and end of each burst, the received signal is passed via filter 30, differentiating circuits 32, 34 to a zero crossing detector 36. A gate 38 produces output pulses indicating the leading and trailing edges of received pulses and controls a bi-stable circuit 40 the resulting output of which is a reconstituted carrier wave. An oscillator 44 is stabilized at 3 MHZ by a phase locked loop including a phase shift detector 42 which receives the 60 KHZ carrier and compares it with the oscillator output fed back via a frequency divider 46. The detector 42 acts to correct the oscillator frequency. From the oscillator output, a frequency divider 48 produces 1 MHZ signal which is fed to a counter 50 to produce "nominal seconds pulses". The mean deviation between these pulses and "actual seconds pulses" at the output of bi-stable 40, should be zero. The actual seconds pulses are decoded at 54 and fed via error checking circuit 56 to a counter 52. The counter 52 counts 1 MHZ pulses in the interval between each corresponding actual and nominal pulse. At the end of 1000 secs the count in 52 is used to vary the number from which counter 50 starts to count. Thereby the actual and nominal seconds pulses are brought into agreement. The decoder 54 also decodes the digital G.M.T. information and the output of a gate 60 is used to produce a display of the correct time.