|Title of Invention||
"A DEVICE USEFUL FOR ACCURATE TIME SYNCHRONIZATION"
|Abstract||A device useful for accurate time synchronization by an outdoor unit with a parabolic dish antenna of 2-3 meters diameter and a Low Noise Converter (LNC) mounted at the dish antenna feed , comprising a low noise amplifier, an S-Band band pass filter, a mixer, an L-Band band pass filter, L-Band amplifier, a second mixer, a Very High Frequency(VHF) band pass filter, a VHF amplifier and a phase locked L-Band local oscilla-* tor(LO) and an indoor unit comprising an Intermediate Frequency (IF) demodulator.|
|Full Text||This invention relates to A Device Useful for accurate time synchronization.
The present invention particularly relates to a device useful for accurate time synchronization using time signals emitted by the Radio Data Sendee - Frequency Modulation (RDS-FM) paging network.
The main usage of this device is to automatically synchronize time and frequency to the 1ST being maintained at NPL, New Delhi. The high accuracy, precision and complete automation makes this device ideal for wide ranging applications like in Television, Radio, Airports, Railways, Telecommunications, Meteorology, Banks, Power generating and distributing units, Seismological, Radioastronomical and geophysical observations, cable TV networks, Technology houses, Industries etc, wherever exact time is essential with an accuracy of better than one second and upto at best a few thousandths of a second accuracy.
At present the general method used to synchronize clocks at the various user agencies listed above is to listen to All India Radio (AIR) or British Broadcasting Corporation (BBC) time signal pips before the hourly news broadcasts or see the time shown on Door Darshan before and after the newscasts. This method is tedious and requires manual operation and can be performed only a few times in a day. Alternatively one uses the satellite based time signal broadcasts on the Indian INSAT satellite or on the US Global Positioning System (GPS). This is an expensive method where high accuracy and automation are achieved for high receiver costs.
Introduction of Radio Data System (RDS) transmission in India adds the digital data capability to the Very High Frequency (VHF) Frequency Modulation ( FM) broadcast on 87.5 MHz to 108 MHz band. Alongwith the stereo/mono FM data, a subcarrier is added which is a harmonic of the the stereo pilot tone. This subcarrier is amplitude modulated with a bi-phase coded signal and the subcarrier is suppressed before modulation on main carrier to avoid cross-
talk. The digital data information is sent in groups of four 26 bit blocks. Each group of 104 bits is one of several types containing different information.
One of the informations transmitted through FM RDS is the time and date of high precision and accuracy based on Indian Standard Time (1ST). This time transmission through INSAT is synchronized with the cesium atomic time standard maintained by National Physical Laboratory (NPL), a constituent laboratory of the Council of Scientific and Industrial Research (CSIR), the time keeping agency of the nation. A Standard Time and Frequency Signal (STFS) receiver at the RDS-FM broadcast centre receives the time transmission from INSAT and provides accurate and reliable 1ST through the RS 232 port. This time signal is used to synchronize the clock of the RDS-FM encoder.
The nearest similar products available in the market are the commercially available Pagers. These devices are able to give a time display only on the front panel in discrete intervals of one minute. No other outputs are available. Also, the time display does not appear when the reception of the VHP signal is impaired. A time synchronization device as described in the present invention has not been found to exist in the market or in the literature
The main object of the present invention is to provide A device useful for accurate time synchronization which obviates the drawbacks of presently known methods and devices .
Another objective of the present invention is to provide a device useful for accurate time synchronization using time signals emitted by the RDS-FM paging network.
Still another object of the present invention is to provide a very low cost solution for accurate time without any wire connection wherever the RDS-FM broadcast is receivable.
In the drawing accompanying this specification fig 1 represents the block diagram of the ^f^ device of the present invention. Fig 2 represents the flowchart of the software used to run the device of the present invention.
The device of the present invention operates in the VHP band. As shown in the block schematic diagram as shown in Fig 1 of the drawings, it comprises (i) an FM receiver (A) which in turn consists of a small whip antenna(l), an FM front end(2), a synthesized LO generator(S), a mixer(3), an IF amplifier(4) and an FM discriminatory), (ii) an RDS subcarrier demodulator-decoder^), (iii)a microcontroller based time signal decoder(7), and (iv) a suitable display device(9) and an output interface unit(10) which are controlled by the microcontroller. There is a real time clock (RTC) (11) which is interfaced to the microcontroller to provide time for situations when RDS reception is not possible. The device of the present invention receives signals from the RDS FM transmission. The received signal is processed and demodulated by the FM receiver to retrieve the baseband signal. This baseband signal is decoded by the RDS demodulator-decoder to retrieve the data and the clock pulses. The micro controller based time signal decoder then extracts the accurate time from these data signals and clock pulses.
Accordingly the present invention provides a device useful for accurate time synchronization which comprises a frequency modulated (FM) receiver (A), the output of the said FM receiver being connected to the input of a Radio Data Service (RDS) subcarrier demodulator decoder (6), the output of the demodulator decoder (6) being fed to the input of a time signal decoder (7), the outputs of the time signal decoder (7) being connected to a local oscillator generator (8) of the FM receiver (A), a time display device (9), and/or to an output interface unit (10), the said time signal decoder (7) being also provided with a real time clock (11).
In an embodiment of the present invention the FM receiver used may be such as is capable to accept different carrier frequencies in the range of 87.5MHz to 108MHz on air in different places.
In another embodiment of the present invention the FM receiver used may essentially consist of a small whip antenna (1), an FM front end (2), a mixer (3), an intermediate frequency (IF) amplifier (4), an FM discriminator (5) and a local oscillator (LO) generator (8), preferably a synthesized LO generator.
In yet another embodiment of the present invention the time signal decoder used may be a single chip microcontroller, at least an 8 bit microprocessor.
In still another embodiment of the present invention the time display unit (9) used may be a digital panel meter with a dot matrix or a seven segment configuration or with light emitting diodes (LEDs) or with liquid crystal display (LCD).
In still another embodiment of the present invention the output interface unit (10) may be a circuit that generates (i) periodic output pulses such as 1 pulse per second (pps), 1 pulse per minute (ppm), 1 pulse per hour (pph) and/or 1 pulse per day (ppd), (ii) 1 pps alternating polarity for driving quartz analog clocks, (iii) time display in the form of video outputs, (iv) serial time code outputs in different protocols such as RS232-C and RS 422-C.
The device of the present invention for time synchronization works using a novel software, the flowchart of which is shown in fig 2 of the drawings. During the initialisation routine, the software initiates the FM receiver chip to autotune to the RDS signal(12). It also reads the time information from the RTC and displays the same(13) so that even in the absence of RDS signal the clock can display fairly accurate time. The microcontroller is interrupted by clock
pulses from the RDS Decoder or, in its absence, by pulses from the RTC. In case of the RDS
interrupt, the software proceeds as follows. The RDS data is read at the interrupt. Each group of data consisting of 104 bits are further subdivided into 4 blocks each containing 26 bits. There is a counter Ccount whose value is checked.(14). If it is less than three then the Programme Identification(PI) code and the group code is read(15). If the PI and group codes indicate valid data(16) then the Ccount is incremented by one(17) following which the program jumps to 25 which is described later. If the PI and group codes are not valid in (16) then the program jumps directly to 25. Now in (14) if the value of the Ccount is equal to three then the data read corresponds to the Time bits which are stored in a buffer memory(18). Following this a counter Tcount is incremented by one(19). The value of Tcount is checked(20) and if it is less than three then the program jumps to 25. If however Tcount equals three in (20) then the three most recently stored values of Time bits in (18) are verified for consistency and this Time is written into the RTC(21). After this both the Tcounter and Ccounter are reset to zero(22) and then the program jumps to 25. In case of absence of the RDS reception the interrupt is by the RTC the Time is read from it(23) following which the Time display register is updated(24). After this the program jumps to 25. In 25 the program does the job of (a) sending to the display device the Time information from the display register(26) and (b) periodically sending the time synchronization outputs to the output interface unit(27). In addition to time, day of the week, date, month and year are also part of the Time message and can also be displayed. The device of the present invention is synchronized with the RDS-FM signal which is available throughout the day. In absence of the transmission, the device of the present invention runs on its internal RTC clock to ensure uninterrupted display of time.
The following example is given by way of illustration of the present invention and should not be construed to limit the scope of the invention.
EXAMPLE - 1
Based on the working principles described above a prototype unit of the device of the present invention was made. In this prototype an FM receiver chip TEA5591 (Philips make) was used. The antenna was a small whip 20cm long. The discriminator output of the FM receiver was decoded using an 8 bit microcontroller Intel 8751. The display was provided using seven segment LED displays FND 507. The microcontroller was also used to initialise the control word for the local oscillator synthesizer of the FM receiver. An RTC MK48T02B was used to provide uninterrupted clock operation even in absence of RDS reception. In the following the features of the protype RDS clock are described.
Time Signal outputs of: the RDS clock are as follows.
1 PPS Analog Slave Clock Drive Output
7 Segment Drive Output for Large Display
1 PPS, 1PPM and 1PPH Signal Output
Digital Display 4 inch seven segment display on the front panel
PC Interface output
PAL composite video and RS 232 bus
Power Source used is 12V, 100mA.
In the following we describe the technical specifications.
Antenna a small whip of length 20 cms.
Input Frequency : 87.5-108 MHz
Bandwidth : 180KHz
Dynamic Range : 10 micro volts to 1 milli volt
Analog Clock Drive : 1 PPS, 1.5V, Alternating Polarity
Compatible for Quartz clocks
Pulse Outputs : TTL, 20 mS
1 Pulse per Second, 1 Pulse per Minute,
1 Pulse per Hour
Display Drive Out : 7 Segment, 6 Digit, TTL
Front Panel Display : 6 Digit, 7 Segment, LED panel 100mm height
Synchronizing Input : 0.5Vp-p to 1.5 Vp-p Video or Sync Signal
Lock Indication : To indicate synchronization to RDS time.
Alarm Facility : Programmable multiple alarms.
PC Interface : RS 232 Bus
The performance of the prototype device of the present invention was tested with the FM transmission at Trivandrum, Cochin and Delhi. The signal reception was clear and the time synchronization was found to be very consistently within a few tens of a millisecond. The device worked within a range of 30 km radius of the FM transmitter.
The main advantages of the device of the present invention are that it is small, compact and fully portable when powered with a battery. Its operation requires no manual intervention and it gets automatically synchronized to 1ST within 1-10 minutes after power up. Ocassional interruptions in the FM signal reception do not affect the the device as it still runs on its internal RTC.
We claim :
1. A device useful for accurate time synchronization which comprises a frequency
modulated (FM) receiver (A), the output of the said FM receiver being connected to the input of
a Radio Data Service (RDS) subcarrier demodulator decoder (6), the output of the demodulator
decoder (6) being fed to the input of a time signal decoder (7), the outputs of the time signal
decoder (7) being connected to a local oscillator generator (8) of the FM receiver (A), a time
display device (9), and/or to an output interface unit (10), the said time signal decoder (7) being
also provided with a real time clock (11).
2. A device as claimed in claim 1, wherein the FM receiver used is such as capable of
accepting different carrier frequencies in the range of 87.5 MHz to 108 MHz on air in different
3. A device as claimed in claims 1or 2, wherein the FM receiver used essentially
consists of a small whip antenna (1), an FM front end (2), a mixer (3), an intermediate frequency (IF) amplifier (4), an FM discriminator (5) and a local oscillator (LO) generator (8), preferably a synthesized LO generator.
4. A device as claimed in claims 1-3, wherein the time signal decoder used is such as
a single chip microcontroller, at least an 8 bit microprocessor.
5. A device as claimed in claims 1-4, wherein the time display unit (9) used is such as
a digital panel meter with a dot matrix or a seven segment configuration or with light emitting
diodes (LEDs) or with liquid crystal display (LCD).
6. A device as claimed in claims 1-5, wherein the output interface unit (10) used is
a circuit that generates (i) periodic output pulses such as 1 pulse per second (pps), 1 pulse
per minute (ppm), 1 pulse per hour (pph) and/or 1 pulse per day (ppd), (ii) 1 pps alternating
polarity for driving quartz analog clocks, (iii) time display in the form of video outputs, (iv) serial
time code outputs in different protocols such as RS232-C and RS 422-C.
7. A device useful for accurate time synchronization substantially as herein described
with reference to the drawings accompanying the complete specifications.
|Indian Patent Application Number||114/DEL/1998|
|PG Journal Number||36/2008|
|Date of Filing||16-Jan-1998|
|Name of Patentee||COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH|
|Applicant Address||RAFI MARG, NEW DELHI-110 001, INDIA.|
|PCT International Classification Number||G06F 13/00|
|PCT International Application Number||N/A|
|PCT International Filing date|