Reference signals of frequency and time. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Radio amateur designer

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In various sectors of the economy, in particular in telecommunications, there is a wide range of consumers who require "binding" (synchronization) of time scales with an accuracy of fractions of a second to thousandths of a microsecond, synchronization of generator frequencies, time and frequency measuring instruments with an error of 10 to 10' 13. The system of transmission of the corresponding signals is managed by the State Service of Time and Frequency of Russia, the scientific center of which is the Institute of Metrology of Time and Space, located in the village of Mendeleevo, Moscow Region. The article describes the reference signals of time and frequency transmitted over various telecommunication channels, tells what technical means this is carried out and how they are used to synchronize the time scales and frequencies of generators.

Reference signals of frequency and time (ESChV) are widely used in various structures of telecommunications. So, with frequency multiplexing of communication channels, messages are transmitted on one sideband of the spectrum of an amplitude-modulated signal with carrier suppression. Its independent recovery at the receiving end of the line requires that the oscillator frequencies be synchronized with an error no worse than 10-9. Time division multiplexing, as a rule, is used when transmitting messages using the pulse code modulation method and allows increasing the information capacity of a communication line by dozens of times. To prevent information loss in such systems, an exact timing of the clock signal generated at the receiving station with respect to the received pulse sequence is required. For the efficient operation of high-speed long-range digital communication systems, it is necessary that the frequencies of master generators in territorial communication centers be maintained with an accuracy of 10 -11.

In television, the quality of directorial editing and mixing depends on ensuring synchronism and in-phase signals from studio and out-of-studio sources. To improve the quality of a television image, it is necessary to form highly stable centralized synchronization signals, reference signals of color subcarriers, and maintain high frequency stability of TV transmitter exciters.

One of the possible directions of using ESChV is the synchronization of timers of individual computers and computer networks.

Here are just a few examples of directions where frequency and time reference signals are needed. In particular, they are also very important for the safety of transport, especially aviation.

The industry produces a wide range of time and frequency measurement instruments of various accuracy - from household time relays and clocks to quantum frequency standards. Setting these tools in the production process, carrying out control measurements and assessing their metrological characteristics require the use of reference tools, including ESChV, transmitted via various communication channels.

At present, the uniformity of time and frequency measurements throughout the world is ensured mainly by means of ESHF transmitted through various means of information, including radio stations operating in the VLF, LW and HF bands, both specialized, intended only for the transmission of reference signals, and and other purposes (radio navigation, communication, sound broadcasting, television), transmitting ESHF on a secondary basis, as well as global navigation satellite systems GLONASS (Russia) and GPS (USA).

For many consumers, including radio amateurs, it may be of interest to check the time signals - SPV ("6 points"), transmitted over the sound broadcasting network, as well as ESCHV transmissions through a specialized LW radio station RBU of the State Time and Frequency Service of Russia, operating with power radiation of 10 kW at a frequency of 66. (6) kHz, and according to the first television program containing coded information about the current values ​​of time.

SPVs transmitted through the sound broadcasting network carry increased information content due to messages about the hour of the day. These signals are designed to check readings and automatically synchronize clocks for technical and household purposes. They represent a group of six radio pulses with a filling frequency of 1000 Hz. The first five pulses have a duration of 100 ms each. The duration of the sixth pulse varies depending on the value of the hour of the day Moscow time from 100 ms to 560 ms after 20 ms in accordance with the expression t=(100+20h) ms, where h is the current value of the hour. The beginning of the sixth pulse corresponds to the beginning of the hour. In the second, third, fourth and fifth SPW radio pulses, signals can additionally be transmitted in the form of sinusoidal oscillations with a level 21 dB below the maximum SPW level, intended for automatic control of audio broadcasting channels and paths. The error of SST in time does not exceed 0,3 s when they are received in the European part of Russia and 0,5 s in the rest of the country.

The RBU radio station uses signals of the DXXXW type to transmit time and frequency, as well as coded information (Fig. 1).

These signals are carrier oscillations of a sinusoidal form with a frequency of 66.(6) kHz, interrupted for every 100 ms by 5 ms. Every 10 ms after interruption, the carrier oscillations are narrowband phase modulated for 80 ms by sinusoidal signals with subcarrier frequencies of 100 or 312,5 Hz and a modulation index of 0,698. Phase modulation of the signal is carried out digitally and in such a way that the average value of the phase of the phase modulated signal is equal to the phase of the carrier oscillations in the absence of modulation. Signals with a subcarrier frequency of 312,5 Hz are used to mark second and minute marks, as well as to mark units in binary coded decimal code when transmitting information about time scales in the first and second 100 ms intervals, counted from the second mark (see below). Signals with a subcarrier frequency of 100 Hz are used to mark zeros in the BCD code during the transmission of information and fill all 80 ms intervals free from the transmission of any information.

Frequency reference signals (EFS) are directly carrier oscillations of the emitted signal, the average daily frequency value of which is consistent with the size of the frequency unit, reproduced by the State standard of time and frequency with an error of no more than 2 x 10-12. As can be seen from the figure, the signal envelope is a 5 ms cut-in, following at a frequency of 10 Hz. These inserts are the reference time signals (ESV). The characteristic points of the ESP of the RBU radio station, which are the inflection points of the rising fronts of the tie-ins, are consistent with the coordinated Russian atomic time scale UTS (SU) with an error not exceeding 10 μs. In this case, the second mark in the signal is the insert, which is preceded by an interval of 80 ms, marked with a subcarrier of 312,5 Hz (Fig. 1). Minute marks are identified by additional marking of the 312,5 Hz subcarrier of two 80 ms intervals preceding the second marker. The information structure of the signal is shown in fig. 2.

The time code transmitted as part of the ESChV is built on the basis of two types of codes: positional-unit - for transmitting the values ​​​​of the difference between the UTC and UTC scales UT1-UTC, and binary decimal with parity - for transmitting other information. Code elements are transmitted every second using carrier modulation in the first and second 100 ms intervals counted from the second mark.

The full time code format contains 120 elements (60 elements in the first 100 ms interval and 60 elements in the second) and is transmitted with a cycle of 1 min. The start of the minute cycle (minute mark) is identified by additional marking of the eighth and ninth 100 ms intervals. The time code format and the content of the transmitted information are presented graphically in fig. 3.

(click to enlarge)

Information about the current values ​​of the time of day is presented in hours (h) and minutes (m) transmitted in the Moscow time scale with UT correction relative to universal time, which is equal to 3 hours during the "winter" time period and 4 hours - during the "summer time" period. "time. Calendar date information includes: the value of the year of the current century (Y), the value of the month of the current year (M), the value of the day of the month (dm) and the value of the serial number of the day of the week (dm). The Julian date information includes the shortened date (TJD), which is the four least significant digits of the numerical value of the modified Julian date (the Julian date is the number of days counted continuously from 12:1 UT on January 4713, XNUMX BC).

ESChV emitted by the RBU radio station provide comparison of highly stable generators (quantum frequency standards, quartz generators) at distances up to 3000 km with an error of (1 ... 50)x10-12 per day and clock synchronization at distances up to 1000 km with an error of up to 0,03, 2 ... XNUMX ms depending on the conditions of reception of the ESHF and the used receiving signaling equipment.

To provide more accurate measurements of time and frequency, ESHF are used, transmitted over terrestrial and satellite television channels as part of television signals. ESChV contain ESCH, ESV and code signals of current values ​​of time. These signals are transmitted on the sixth line of each odd field. The shape of the signals and their location in the sixth line are shown in fig. 4.

The span of the input signals is G.35±0,05 of the full video signal span. The sixth line is divided into three intervals, and each has its own type of signals. For the transmission of the ECH, I interval with a duration of 15 μs is used. ESCs are transmitted in bursts consisting of 15 oscillatory periods at a frequency of 1 MHz, which always start with a positive half-wave in the burst. The relative daily error of the ESP in Moscow does not exceed 2 · 10-12.

For the transmission of ESP, the second interval is intended with a duration of 12 μs. Information about the time scale is carried by a characteristic point corresponding to the middle of the ESP front. the time position of which is consistent with the UTC(SU) scale with an error of no more than 0,5 µs. The ESP repetition frequency is 1 Hz, the duration of the rising front is 20 ns.

For the transmission of coded information about the current values ​​of time - TZV (h, min, s), the III interval with a duration of 15 μs is intended. Information about the TVT is transmitted using a binary-decimal code (Fig. 5) for 24 frames (full cycle - 25 frames per 1 s) using radio pulses of various frequencies. The frequency of the signal corresponding to the log. 1 code, equal to 1,66 MHz, log. 0 corresponds to a frequency of 2,5 MHz, and a radio pulse with a frequency of 1 MHz in the 25th frame is used as a marker for the end-of-cycle signal. To improve noise immunity, parity check bits Rs, Rmin and Rch have been introduced into the TZV code. The TZV code is transmitted with a cycle of 1 s continuously during the entire transmission time.

The central point for the formation and input of ESCHV into the sixth line of television signals of the first ORT channel and its duplicates transmitted via satellite channels "Orbit 2, 3, 4" is located at the technical television center (Moscow, Ostankino). Depending on the methods and means used, the clock synchronization error from television ESChV ranges from 0,02 to 10 μs, the frequency comparison error is (1 ... 10) x 10-12 per day.

To inform consumers of ESChV, the State Time and Frequency Service of Russia (GSVCh) issues and distributes a number of special bulletins upon request.

As can be seen from the above, ESChV of one type or another, containing coded information about time and date, are available almost throughout Russia. This opens up a wide field for consumers in the development of household radio clocks, as well as devices that make it possible to clock enterprises and cities, synchronize computer network timers, and automate measurements with high accuracy and reliability. This is all the more relevant, since the industry currently produces a very small range of equipment using ESChV, and the need for it is great.

The industry has mastered the production of two types of electronic clocks, in which the current time values ​​are corrected according to the "6 points" FPV transmitted over wired broadcasting networks (radio broadcasts) and radio stations broadcasting programs "Mayak" and "Radio-1": 1 - receiver of time verification signals (PSPV-1); 2 - meter of current values ​​of time and frequency of the mains (IVCh-1).

The PSPV-1 receiver is made in the form of a board inserted into a free slot of a PC/AT personal computer. and is used to synchronize or "time reference" computer timers and register the time and date of an event in it.

PSPV-1 is designed to receive signals from VHF radio stations, store and issue information about the current values ​​of the time of day (h, min, s) and date (year, month, day), allocation of SPV, automatic correction (setting) of the TTZ, output of information about time and date from the receiver's timer to the monitor and to the ISA personal computer bus, input of time and date information from the receiver's timer into the computer's system timer (manual or automatic according to the "6 points" SPV), displaying time information on the receiver's timer on the monitor screen and computer system timer and the difference between them. The error in setting the time in the computer timer relative to the middle of the edge of the sixth FPV signal "6 points" during correction does not exceed 0,1 s.

The IVCh-1 meter is made in the form of a microprocessor module and is intended for measuring (storing) and issuing information about the current values ​​of time, date and frequency of an industrial power network with subsequent transmission of measurement data via the RS-232 port to a personal computer. This device provides measurement of the mains frequency, installation, storage, indication on the scoreboard and output of information about the current values ​​of the time of day (h, min, s) and date (year, month, day), allocation of free time, automatic correction of the current values ​​of the time of day in the timer IVCh-1. output of information about time, date and frequency of the network through the RS-232 port. In IVCH-1, the serviceability of the power supply circuits, the emergency situation, the correctness of the reception of the SPV are displayed. Accuracy of time storage with hourly correction according to SST - ±20 ms, in the absence of correction - ±2 s/day.

The industry also produces SYNCHRONOMETER ChK7-50, designed to synchronize or "time reference" time scales, determine the current values ​​of the time of day (h, min. s) and date (year, month, day), fix the moments of events using reference frequency signals and time transmitted by the RBU radio station, information transmission via the IEC 625 interface.

SYNCHRONOMETER ChK7-50 can be used in metrology, astronomy, geophysics, energy, etc. The error of automatic synchronization of the time scale is no more than 20 µs. receiver sensitivity - no worse than 2 μV.

Authors: V.Borisochkin, S.Kagan, G.Cherenkov, village of Mendeleev, Moscow region.

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