CA1167649A - Method of automatic adjustment of self-contained radio-clock by means of time mark - Google Patents

Abstract

A time measuring method is combined with an automatic rate correction process in a digital or quasi-analog chock; a clock rate deviation is repeatedly measured, in a predetermined lock-in range, derived from the clock oscillator frequency, by means of a time mark received from a transmitter; the deviation data are stored and used for correcting the clock rate and the oscillator frequency whereby the stored data are maintained until the arrival of the next time mark.

Description

I 1~7619 This invention relates to a method of and a device for adjusting a clock by a time mark. The clock can be a digital clock or a clock indicating in quasi-analog manner with the help of a stepping motor, and that -- apart from the first installation or a service -- it never needs an adjustment, even after a long opera-tional period during which a time mark is missing, and does not have a distinguishable speed- or rate deviation. The clock according to this invention works accurately under extreme interference and is power-saving.
The term "self-contained" radio-clock in this disclosure means an automatically working radio-clock which is independent of a manual adjusting process. The term "time mark" denotes a part of a modulation envelope that is transmitted by wire or wirelessly to indicate the time reference signal given by a transmitter.
The term "radio-cloçk" denotes a clock receiving the time mark.The term "clock radio" denotes a clock with a radio set.
The known methods of adjusting radio-clocks can be divid-ed into three categories: l. synchronization, 2. triggering, 3, demodulation and direct indication of a coded time information.
For all these methods there are numerous variations and circuits including the necessary backup time, and a great number of publi-cations are available. The first category includes analog or digital clocks whose internal time base is constantly or partly corrected in relation to a received reference frequency by means of automatic frequency control or phase comparison, as e.g. describ-ed by Tetzner, Karl: "Funksynchronisierte Uhren" in: Funkschau 1976, vol. 15, p. 623 (Franzis-Verlag M~nchen, Federal Republic of Germany) or by Marti, Raymond: "Selbsttatige und fortlaufende Zeiteinstellvorrichtung einer Uhr'l in German published patent application (Auslegeschrift) DE-AS 1,773,406. There are also applications known that derive the time base of the clock from .~ ~

6 ~ 9 1 the carrier frequency of one (or several) transmitter(s). In this case an additional change-over to a second time base is re-quired (backup time), as described by Schreiber, Herrmann:
"Steuerung einer Gebrauchsuhr durch Zeitzeichensender" in Funk-schau 1977, vol. 2, p. 96 and vol. 3, p. 137 (Franzis-Verlag Munchen, Federal Republic of Germany). The second category in-cludes digital clocks that work independently with a varying amount of accuracy and that are set at nominal value at a fixed time (mostly 0 o'clock) by means of a time mark, as e.g. describ-ed by Beck, J.: "Korrekturautomatik f~r Digitaluhren" in Elektor 1974, vol. 7, p. 79 (Elektor Verlag GmbH Gangelt, Federal Republic of Germany). The third category divides into two methods: 3.1 the time code transmitter is constantly received, as e.g. describ-ed by Weiss, Reinhard: "Uhrzeit- und Norma'frequenzempfanger f~r DCF 77 mit Gangreserve" in: Funkschau 1976, vol. 22, p. 964 (Franzis-Verlag M~nchen, Federal Republic of Germany), 3.2 the ti~ code transmitter only temporarily serves for adjusting the radio-clock, as e.g. described by Prof. Dr.-Ing. Hilberg, Wolfgang:
"Funkuhr-Einstellung" in the published German patent application (Offenlegungsschrift) DE-OS 2,715,096: in this case, the switch-ing-on of the receiver is dependent on the rate of the clock, and the exceeding of the backup time is indicated; or the method of Mukaiyama, Fumiakai, Suwa, Nagano: "Automatisches Korrekturverfahren fur eine elektronische Uhr", according to the published German patent application (Offenlegungsschrift) DE-OS 2,539,224, where the codedly transmitted time information serves as correction value for the digital clock at optional instants. The third category also includes receivers, e.g. television sets, that are not radio-clocks primarily but indicate the correct time after pressure on a push-button, as e.g. developed by AEG-Telefunken and described 1 1 67~9 1 in the magazine "Elektrotechnik" vol 6, 1972, p. 29 (Vogel-Verlag KG, Wurzburg, Federal Republic of Germany) and under the title:
"Kunftig nur noch Atomzeit". Parallel to these there are various time measuring methods that define the rate of a clock by means of a transmitter signal and eliminate it by special provisions, as e.g. described by Maire, Bernard, Marin: "Elektronisches Zeit-messgerat mit automatischer Korrektur der Gangabweichung" in the published German patent application (Offenlegungsschrift) DE-OS

2,851,223; in this case, the rate of a clock in second steps is manually measured by means of a time mark over a long time interval, and then stored; the clock automatically corrects its stored rate within the next, same time intervals as long as a new correction invitation is signalized to the set user.
The methods mentioned have different advantages and dis-advantages of which only the disadvantages to be emphasized are enumerated here: as to the 1st category: relatively long turn-on time of the receiver, which raises the susceptibility and the re-quired energy; relatively short backup time; no self-contained operation in the original sence. As to the 2nd category: re-latively inexact time indication after a longer missing time mark,because the rates of the subsequent, not corrected time intervals add up continuously; triggering is at 0 o'clock (counter reset) which makes it impossib~e to tune out interferences occurring regularly at that time. As to the 3rd category: a time code transmitter with a sufficient field intensity must be receivable which presupposes relatively elaborate and expensive receiving devices; the decoder circuits are relatively elaborate; the mounting of quasi-analog indicating clocks is not possible. Be-sides the manual operation, the aforedescribed time measuring method has the disadvantage that the rate of the clock reaches a ~ 1 ~7649 1 relatively high value before correction begins.
A general object of the present invention is to over-come the aforementioned disadvantages. More particularly, an ob-ject of this invention is to provide a fourth category of radio-clocks which presents a combination of a time measuring method for the rate of the clock with an automatic adjusting process typical for radio-clocks, the result of which is a self-contained operation.
According to the method of this invention, the rate deviation of the clock is measured both as to its magnitude and its direction by means of a time mark with defined equal time in-tervals, the deviation is stored and then used for the correction of the rate and the oscillator frequency of the clock. The turn-ing-on of the time signal receiver, the fixing of the lock-in range for the time mark, as well as the decoding of the time mark is also performed by this oscillator frequency. In spite of a very short turn-on time of the time-signal receiver, the lock-in range must be chosen wide enough to ensure that the time mark is within the limit value, even under the worst operational condi-tions. After a missing time mark, a false measurement and falsecorrection is inhibited. In this case, the aforementioned correc-tion is performed with the latest values stored, the result of which is a high backup time. Furthermore, the method has been worked out to be ~pplicable for various clock installations. In this case, the master clock can, among other things, be regarded as amplifier stage for the time mark, providing all slave clocks with an amplified time mark. Provided that there is a uniform time-signal transmitted by all radio and TV stations, time code stations and master clocks, the time-signal receiver can auto-matically adjust to the transmitter with the highest field in-1 tensity, and can select another transmitter after repeated miss-ing time mark. Likewise a displacement of the time-signal receiv-er into commercial radio and TV sets is possible, so that the al-ready existing receiving device can be used by the radio-clock as well.
The invention presents the following advantages:
1. the maximum rate can be kept smaller than the display resolu-tion; 2. the backup time is very high; 3. the method can be applied to digital clocks as well as to quasi-analog indicating clocks; 4. the time-signal receiver is turned on periodically for very short moments, the result of which is a very high freedom from interference and 5. energy economy; 6. the correction of the indicated value need not necessarily be at 0 o'clock; 7. the method can be applied to clock installations; 8. at the clock manufactur-ing the oscillator alignment can be avoided.
Provided a uniform time-signal which can be established and transmitted by far less problematically than a coded time information, further advantages can be provided: 9. the decoder circuits are laid out comparatively simple and can be produced in large numbers of pieces; 10. it is possible to displace the time-signal receiver into commercial radio and TV sets, so the already existing receiving device for this equipment can be useful for the radio-clock as well moreover the radio-clock can be produced more cheaply; 11. the time-signal receiver can be produced less expensive-ly than a receiver for coded time information because 11.1 a larger field intensity can be counted on (receiver locks in place to transmitter with highest field intensity); 11.2 the decoder circuit is more simple;
11.3 higher demodulation distortion is admissible; 11.4 the power supply can be smaller.

1 - The novel features which are considered characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construc-tion and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of preferred embodiments when read in connection with the accompanying drawing.
FIG. 1 shows in a flow chart the method of this inven-tion;
FIG. 2 shows in a block diagram the functional sequence of FIG. l;
FIG. 3 shows the time diagram of the indication correc-tion;
FIG. 4 shows a block diagram of the time-signal receiv-er;
FIG. 5 shows schematically a complete concept of the radio-clock according to this invention;
FIG. 6 shows the application of the time-signal receiv-er in commercial radio and television sets;
FIG. 7 shows the principle of function of a clock in-stallation according to the invention;
FIG. 8 shows schematically another embodiment of the clock installation according to the method invented; and FIG. 9 shows an example of an appropriate time-signal for the method of this invention.
The flow chart in FIG. 1 shows the time sequence of the most important signal conducting lines of the block diagram in FIG. 2. These signal conduits are denoted by encircled reference numerals corresponding to thoee in FIG. 2. This block diagram is intended merely for illustrating the function of this invention ~ ~ 67~'~9 1 and in practice is substituted by a computer program. The rate of the clock 49 is determined by the frequency stability of the os-cillator 30. In order to measure this rate, a comparison with a supposedly "correct" time interval must be possible. As there is no absolutely correct time scale, the basis for clock applications has to be the legal time transmitted by non-uniform time-signals by radio and television stations and time code transmitters. The following disclosure supposes, however, that a uniform automatical-` ly evaluable time-signal is transmitted by all radio and television stations, so that the method described here can fully take effect.
The clock is put into operation by means of the switch f that turns on the start automatic 48 and the time-signal receiver 45. In case the clock is in operation it can be stopped by means of the stop-pushbutton e. For quasi-analog indication clocks, the hand setter is set to the time reference or held at that position.
The next time mark 3 or 5 gets into the clock via the start auto-matic 48 and adjusts all registers -- according to the time re-ference given -- to the desired value, and starts the time counter.
Now the clock 49 works automatically without any influence of the transmitter with the accuracy of its quartz-oscillator until the arrival of the subsequent time mark 3 or 5. Parallel to the first time mark 3 or 5 received, the quiescent is produced via the reset ; path of the start automatic: the flip-flop 47 is reset via the OR-gate 41~ which interlocks the time mark output of the AND-gate 46; the clock counter 40 is brought to 0 and the flip-flop 38 is brought to a rest position via an OR-gate 36, so that clock signal 1 cannot get into a clock counter 40 via an AND-gate 39; a switch-ing-on stage 43, 44 of the time-signal receiver 45 is brought to the "off"-position via an OR-gate 35; further, the registers in the adjusting logic 31 are set to the desired value, and the con-1 ten~s of the memory for sign 23 and of the memory for difference time 26 are brought to 0. A short time later~ the time-signal receiver 45 and the start-automatic 48 are turned off by means of the switch f which ends the start. A temporal preselection signal 1 of the clock 49 turns on the time-signal receiver 45 via the switching-on stage 43, 44, (e.g. after 23 h. / 59 min. / 50 s.) and opens the AND-gate 39 by means of the flip-flop 38, so that clock signal 1 can get into the clock counter 40. The next in time signal 2 is given by the clock counter 40, and releases the time mark output of the time-signal receiver 45 via the flip-flop 47 and the AND-gate 46, resets the registers in the difference time measuring stage 24 and in the priority logic 21, and releas-es via the AND-gates 22, 25 the carry of information from prior-ity logic 21 and difference time measuring stage 24 to the memory for sign 23 ane the memory for difference time 26. The priority logic 21 now accepts the time mark 3, 5, or the periodic pulse 4 from the clock counter 40. In case the periodic pulse 4 arrives before the time mark 5, thereiis a positive sign in the priority logic 21 (the signàl for the memory for sign e.g. has the poten-tial H); in the opposite case, there is a negative sign by difini-tion (the signal for the memory for sign e.g. has the potential L).
At the arrival of the 1st signal 3 or 4, the difference tim measuring stage 24 is started by the priority logic 21 whereby counting pulses of clock signal line 2, leading from the clock counter 40 to the difference time measuring stage 24 and to the correcting stage 27, are counted and determine the resolution of the time measuring stage for the rate of the clock 49. The differ-ence time measuring is then ended by the last arriving signal 4 or 5 via the path of priority logic 21. The signal 7 of the clock counter 40 then interlocks the time mark 3, 5 via OR-gate 41, _ g _ I 1 67~9 1 flip-flop 47, and OR-gate 46. The next output 8 of the clock counter 40 turns off the time-signal receiver 45 via OR-gate 35, flip-flop 43, and OR-gate 44, and with the same signal 8 trans-mits the measuring values from priority logic 21 and difference time measuring stage 24, via the OR-gates 22, 25 into the memory for sign 23 and the memory for difference time 26. When these data are stable at the correction stage 27 and have been evaluat-ed, the correction can be initiated from the clock counter 40 via the signalling line 9. The indication correction is performed by means of the pulse stage (1) 29, pulse stage (2) 33, and the OR-gate 37 in a way that the rate values stored in the memory for sign 23 and the memory for difference time 26 are cancelled. Here-by the pulse stage (1) 29 converts clock signal 1 (FIG. 3a) of the oscillator 30 into a square-wave of the impulse ratio 4 (FIG. 3b).
In normal operation, this square-wave reaches the clock 49 as a clock signal via the OR-gate 37 and the noise filter 42. If, according to the measurement result, the clock 49 is fast, the latter clock signal is inhibited by the correction stage 27 via the OR-gate 28 in the pulse stage (1) 29, until the measured rate is compensated. If, according to the measurement result, the clock is slow, a center pulse relative to the clock signal (FIG.
3c) is released by the correction stage 27 via the OR-gate 32, in the pulse stage ~2) 33 whereby the aggregate signal with the im-pulse ratio 2 (FIG. 3d) reaches the clock 49 via the OR-gate 37 until the measured rate is compensated. Parallel to the indica-tion correction it is advisable to perform the oscillator correc-tion, e.g. the digital correction, as described by Dipl.-Ing.
Gollinger, Wolfgang, in: "Elektronische ~uarzuhr mit integrieten Schaltungen" in published patent application (Offenlegungsschrift) DE-OS 2,362,470 of December 15, 1973 and schematically illustrated ~ ~ 67~-~9 1 in FIG. 5. The correction stage calculatingly counteracts to the rate of the clock 49 in this oscillator path, so that there is a closed control loop. The end of all correction processes is :indicated by the correction stage 27 by means of a signal 10 which effects the reset of the clock counter 40 and the flip-flop 38 via the OR-gate 36. In the event of a missin~ time mark, the counter in the difference time measuring stage 24 reaches its maximum value and sets the flip-flop 34 with its output or over-flow 6. By this, the carry pulse 8 has no effect, so that the following indication correction is performed on the basis of the values lastly stored in the memory for sign 23 and the memory for difference time 26. The oscillator correction is inhibited by the flip-flop 34, so the automatic control system is interrupted in order to preserve the high backup time. The signalling line DST (daylight saving time) from the clock 49 to the adjusting logic 31 presupposes a computer-regulated date clock. H-potential corresponds e.g. to summer time, L-potential to winter time. The potential variation on this signalling line produces the aimed adjusting process of one hour respectively by means of the afore-described method for indication correction. As this adjustingprocess takes a relatively long time, and the indication informa-tion is incorrect during this time, the display resolution should be one second in any case in order to make visually noticeable the following information: the clock is too fast, or the clock is not in operation. This signalling is sufficient for outsiders, even without operating instructions, to disregard the display.
Pronest to interference is the time mark 3, 5, whose signal line is subjected to a closer study. Interference pulses outside the lock-in range (FIG. 1) have no effect whatsoever.
Interference pulses within the lock-in range only have an effect I ~ 67649 1 if they arise before the arrival of the time mark 3 or 5. In this case, there is a high probability of a continuous interfer-ence, i.e. a high probability of an interference impulse sequence ranging over the whole lock-in range. ~ere, only the first in-terference pulse being nearest to the bottom limit (FIG. 1) has an effect. Hence it is simulated that the clock is slow. If, during the automatic oscillator alignment, provisions are made for the clock to be really slow, then the lock-in range -- in spite of misinterpreted time marks -- will not shift too far even after re-peated interferences. In other words: the time mark 3 is expect-ed within the first half of the lock-in range; whereby the inter-ference pulse has only little action time. It must be regarded that the lock-in range with the periodic pulse 4 from the clock counter 40 changes in relat~on to the time mark 3, 5, whereas the time mark itself 3, 5 can be regarded as stationary.
FIG. 4 shows a detailed block diagram of the time-signal receiver 45. The radio tuner 61 -- as described before -- has a simple design. The transmitter tuning is controlled by voltage.
The receiver-microcomputer 68 automatically sets the radio tuner 61 to the transmitter of the highest field intensity after the switching-on by the OR-gate 44 and the switchinq-on stage 64.
This is e.g. done by evaluating the AGC voltage supplied to the receiver-microcomputer 68 via the amplifier 62 and via the A/D-converter 66. First the computer program checks the whole receiv-ed frequency range by means of the tuning voltage transformed by the D/A-converter 65 and stores the respective AGC voltage values.
Then it locks the radio tuner 61 at the transmitter having the highest field intensity in order to increase the probability of a trouble-free reception. If, as is done now, the time-signal is transmitted at nearly each full hour by all transmitters, there t J ~64g 1 is the possibility -- in time information border areas -- of re-ceiving an adjacent transmitter outside the time information border, which is not possible with transmitted coded signals. The receiver-microcomputer 68 can simply register a repeated missing time mark, as it also has to perform the time mark decoding. In this case, it searches the transmitter of the second highest field intensity.
If the radio tuner 61 is to be used as a clock radio at the same time, a changeover to manual tuning by means of the switch g is advisable. The then tuned-in transmitter is now used as a time mark transmitter as well. In this operating mode, the start-automatic 48 must be interlocked via the OR-gate 69, and the re-ceiver-microcomputer 68 must be changed over to a different soft-ware loop. There may be the necessity of selecting the time mark transmitter by manually tuning-in a certain transmitter (e.g. time code transmitter). This transmitter selection can then be stored by actuating the pushbutton h which ensures that the receiver-microcomputer 68 will then automatically select this transmitter.
Pushbutton i can cancel this operatimg mode: if the program re-gisters a 0 when sensing the memory location for the given trans-mitter, it then selects the transmitter of the highest field in-tensity. The time-signal LF to be decoded (FIG. 9) is amplified by the amplifier 63 and becomes high enough to be used as square-wave with defined logic levels. The flip-flop 67 improves the decodability, as it halves the mark frequency, and provides an exact impulse ratio of 2.
The application of the method of this invention for clock installations is as follows:
The most simple and least expensive embodiment of a clock installation according to this method includes a master _ 13 ~

t 1 675.~9 1 clock according to FIG. 5, and quasi-analog indicating slave clocks with stepp motors 82. The controlling of the slave clocks is done by a single signalling line that leads the second step with correction to each slave clock. So the installation of the slave clocks is restricted to one twin wire -- without power supply --, which recommends this method for applications where ex-plosion hazards exist.
Similarly simpl~ is the embodiment of a clock installa-tion according to FIG. 7. The master clock is worked out as in FIG. 5, and so are the slave clocks; the latter, however, have no time-signal receiver 45. The controlling of the slave clocks in this embodiment is done by means of the time mark. As a conse-quence, the slave clocks work trouble-free, need no adjustment after a master clock failure (exploitation of high backup time) and can be equipped with a digital display 81. Very often slave clocks are installed in places hard to get at and exposed to ex-treme environmental influences; so the service should be easy for this type of clock in particular. As the method of this invention presupposes a computer-directed clock anyway, it is possible, with-out any additional elaboration, to provide for outputs for thedata exchange (the indicated value) via standardized interfaces between master clock and slave clocks. FIG. 8 shows an example, where the controlling of the slave clocks is done again by means of the time mark, resulting in trouble-free operation with a high backup time; moreover, there is the additional possibility of in-dicating, in a central control station, the defective operation of a slave clock by the cyclic checking of all slave clocks.
After a preformed service, a precision adjusting process derived from the master clock is also possible. The requisite condition for this process is the possibility of addressing each slave clock 1 from the master clock, and the simple setting and recognition of the specific addresses in the slave clock. In accordance with this invention, this problem can be solved comparatively easily by means of thumbwheel switches 91 (FIG. 8). Then there is the possibility of performing adjusting process for DST coming from the master clock.
Adjustment at the transmitter end:
Automatic timing controls or readjustment steps for the self-contained radio-clocks must be designed and dimensioned for 10 functioning under the worst operational conditions. A wide lock-in range, however, means a susceptibility to disturbances and a high amount of energy consumed by the clock, because the time-signal receiver is turned on for a longer period of time. At the present level of technology, excellent resonators can be produced to keep the daily rate deviations of a clock low. The highest de-viation arises at a time scale jump, i.e., at leap or switchover seconds which a radio-clock must constantly take into account lest they degrade the whole conception. Hence it is advisable to part-ly depart from the method of leap seconds and to perform the adaptation of the mean solar time to the average atomic time in smaller time scale jumps. Advantageous is the splitting of the leap into 8 (23) equal parts, that is 0.125 second steps which are taken into consideration on 8 successive days before the calculat-ed moment, the last calendar days of a UTC-month (UTC = Coordinat-ed Universal Time), preferably at the end of June or December.
Here the general principle of the leap second internationally agreed upon is kept up. If more than one time-signal is trans-mitted per day (there should be 2 at least, displaced by 12 hours), then a time scale jump in each time-signal of a time interval (e.g. of one day) must be taken into consideration in the same way.

I 1 6~tfi~9 1 Practical experience shows that one correction of the clock per day is sufficient. In order to tune out periodically interfer-ing transmitters regularly interfering at the same time of the day it is advisable to fall back to a second time-signal. An-other advantage of this is the independence of one particular time of the day when putting the clock into operation for the first time, or after a service. Hence all radio stations should oblige to always transmit the uniform time-signal at two fixed moments of the day displaced by 12 hours. From the various possi-bilities for an appropriate time-signal granting an automatic evaluation one solution has been worked out permitting the layout of simple time mark decoders and coders, being acoustically notice-able and having a duration of only 3 seconds (FIG. 9). The LF-modulation frequency of 1000 Hz was chosen because in communica-tion engineering it serves as reference frequency for many para-meters, and moreover can be made audible. The chosen duration of

3 seconds in all is an advantageous compromise between unnecessar-ily long (which means interference-prone) and too short (which means insufficient selection from an optional LF-signal). It must further be stressed that all decisive time intervals can be deriv-ed by binary dividers from a usual "clock frequency", e.g. 215 Hz or 222 Hz, for which sufficient resonators are available. This advantage is valid for both the time mark coder and decoder cir-cuits. The equally selected time intervals cooperate to a comput-er evaluation, because then software loops or subroutines can be applied.
It will be understood that each of the elements describ-ed above may also find a useful application in other types of con-structions differing from the types described above.

Claims (8)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of automatic adjustment, by means of a succession of reference time marks each transmitted by a transmitter, within a predetermined time range of a self-contained radio-clock including a time mark receiver and oscillator and means for generating periodic pulses, comprising the steps of deriving from the oscillator frequency a predetermined lock-in time range exceeding the time range of the time mark; measuring periodically data relating to a deviation of the rate of the clock, such as the magnitude and direction of the deviation, by comparing a time mark with a periodic pulse from the clock; storing the measured deviation data; thereupon correcting the rate of the clock according to the stored deviation data without changing the stored data until the next time mark arrives.

2. A method as defined in claim 1, comprising correcting periodically the oscillator frequency according to the stored data.

3. A method as defined in claim 1, wherein the time mark receiver is switched on shortly before the limits of the lock-in range, and then switched off shortly after said limits.

4. A method as defined in claim 1, wherein periodic clock pulses are derived from the oscillator frequency within the lock-in range, and the oscillator is automatically aligned when the time mark is received within the lock-in range.

5. A method as defined in claim 1, wherein the time marks are transmitted by a plurality of transmitters and the time mark receiver is controlled by a computer to receive a time mark from the strongest transmitter and, in the event of a missing time mark, to tune up a next strongest transmitter or a preselected transmitter.

6. A method as defined in claim 1, wherein said time mark receiver is constituted by a standard radio or television receiver or by the clock.

7. A method as defined in claim 1, for use in a time-keeping installation having a master clock and at least one slave clock, comprising addressing or adjusting the time indication of the slave clock by coded switching means provided at the master clock.

8. A method as defined in claim 1, wherein in the case of a time scale jump at the transmitter, a time scale jump of one second is divided at the transmitter into a plurality of smaller time scale jumps whereupon the smaller time scale jumps are trans-mitted in several consecutive time intervals.