RU122810U1 - TRANSFORMATION AND RECORDING SYSTEM FOR RADIO ASTRONOMIC INTERFEROMETER - Google Patents

Abstract

1. A system for converting and recording signals for a radio astronomical interferometer, containing n signal conversion channels, each of which includes a bandpass filter of the input signal, an analog-to-digital converter connected to a signal generator of a readout clock frequency, and a first digital comparator of signal samples connected to a calculator rms value of signal samples, as well as a pulse generator of seconds of the current time and a generator of the output data code connected to the output data buffering device, characterized in that an m-channel demultiplexer connected to the said analog-to-digital converter, an rms calculator is introduced into each signal conversion channel. the values of the signal samples and the readout clock signal generator, (m-1) additional digital comparators of the signal samples connected to the rms calculator of the samples and the data code generator, and the divider h frequency, connected between the read clock signal generator and the clock inputs of all digital sample comparators. 2. The system for converting and recording signals according to claim 1, characterized in that the second pulse sensor is connected to the blocking inputs of the analog-to-digital converter in all channels of the signal conversion and recording system. The signal conversion and registration system according to claim 1, characterized in that switchable digital inverters are installed at the inputs of the digital comparators with odd ordinal numbers.

Description

The utility model relates to radio astronomy and is intended for use on radio telescopes operating as part of complexes of radio interferometry with extra-long bases (VLBI). VLBI complexes, for example, Kvazar-KVO, provide the most accurate coordinate-time and ephemeris measurements and are widely used in basic scientific research in the interests of astrometry, geodesy, ephemeris astronomy and other fundamental sciences, as well as in solving many applied problems - coordinate temporary support of the country, maintenance of the GLONASS global satellite navigation system, long-distance space navigation, earthquake and asteroid hazard prediction, etc. (see, AMFinkelshtein, A.V. atov and S. G. Smolentsev Radio interferometric network “Quasar” - scientific tasks, technology and the future // “Earth and the Universe” No. 4. 2004. S.12-25; AM Finkelshtein and other radio interferometric network “Quasar-KVO” - basic coordinate-time support system // Transactions of IPA RAS. Issue 13. St. Petersburg: “Science. 2005. P.104-138).

The most important part of the VLBI radio telescope equipment is the radio interferometric signal conversion system (SPS), which select signals in specified parts of the frequency range, convert them to video frequencies (up to 16 or up to 32 MHz), filter them and convert them to digital pulse streams that are recorded and then transmitted from all radio telescopes of the VLBI network to the center of correlation processing (CSC) of VLBI data. At present, multichannel ATPs are used on radio telescopes of high-precision VLBI networks, which contain from 8 to 16 video converters (ATP channels). In such ATPs, broadband noise signals received from space sources are distributed over video converters together with the intrinsic noises of the receiving system of the radio telescope. In the video converter, the noise signal is transferred to the frequency band (usually 8, 16 or 32 MHz), with the upper and lower side frequencies being separated by the phase method. Next, the noise signals are filtered and quantized in amplitude (converted into binary pulse flows corresponding to specified threshold levels of quantization). The obtained quantized signals are recorded (for example, on hard magnetic disks) and transmitted to the CSC.

The most modern ATP include 8- and 14-channel VLBI 4 and Mark IV DAS systems manufactured in the USA (see Petrachenko WT VLBI Data Acquisition and Comparison // Proc. Of 2000 General Meeting of International VLBI Service for Geodesy and Astrometry. Germany. 2000. P. 76-89), as well as the Russian-made ATP PI LLC (see A.V. Ipatov, N.E. Koltsov, L.V. Fedotov, Radio Interferometric Terminal of the Badary Observatory // Devices and Technology experiment. 2009. No. 1.) and P1002M (see S.A. Grenkov, N.E. Koltsov, E.V. Nosov, L.V. Fedotov Digital radio interferometric signal conversion system // Instruments and experimental equipment. 2010 No. 5. S.60-66 )

For all these SPS, the frequency band of the recorded signals is limited by the passband of the phase separation devices of the sideband signals and filters of the video converter. Therefore, such ATPs are mainly used on radio telescopes with antennas of a sufficiently large diameter (usually from 22 m to 70 m), which allows for a limited time of signal reception and registration to obtain correlation responses of the required quality from reference cosmic sources very distant from the Earth (spectral densities the power flow of the received radio signal is about (0.5-1) -10 ^-26 W / m ² · Hz). In promising VLBI networks, on radio telescopes with high-speed antennas of small diameter (6-13 m), ATPs with video converters do not provide the necessary sensitivity of radio interferometers. Here, ATPs are needed that record signals with wide (hundreds of MHz) spectral bands (see, for example, Alan R. Whitney. Wide-Bandwidth Digital Backend System for VLBI // Proc. Of the 18 ^th European VLBI for Geodesy and Astrometry Working Meeting. 12-13 April 2007. Vienna. P. 39-44; G. Tuccari, S. Buttaccio, G. Nicotra. DBBC-A Flexible Environment for VLBI and Space Research: Digital Receiver and Back-end System // Proc. Of the 18 ^th European VLBI for Geodesy and Astrometry Working Meeting. 12-13 April 2007. Vienna. P. 45-49).

The system (prototype) closest in purpose and technical essence is the SPS R1002M, which, unlike other systems, contains video converters with digital signal conversion (see, S.A. Grenkov, N.E. Koltsov, E.V. Nosov , L.V. Fedotov Digital Radio Interferometric System for Signal Conversion // Instruments and Experimental Technique. 2010. No. 5. P.60-66).

The P1002M system is connected to the outputs of the intermediate frequencies (IF) of radio astronomy receivers and contains 16 video converters that convert the IF signals to video frequencies (up to 32 MHz). Each video converter is made according to the scheme proposed in the description of the patent for utility model No. 80616. The video converter contains an input amplifier, an analog quadrature mixer, to the outputs of which are connected two analog-to-digital converters (ADCs) controlled by a clock signal generator (GSTCH), and a digital signal converter (DSP) on a programmable logic integrated circuit (FPGA). At the outputs of the quadrature mixer, the signals are phase shifted 90 ° relative to each other. In DSPs, digital samples of these signals are phase shifted by another 90 °, resulting in a digital separation of the signals of the upper and lower sidebands. The signals of each sideband in the FPGA are filtered and converted into two pulse sequences in accordance with the rules of 2-bit quantization of signals at VLBI. For this, the FPGA calculates the root mean square values (RMS) of the digital signal samples coming from the ADC. In accordance with the VSI-H data stream practice adopted in practice, VSI-H information pulse sequences from all video converters accompanied by a meander of a clock frequency (usually 32 MHz or 64 MHz) and 1PPS (one pulse per second) pulses, marking the beginning of the next seconds of the current time, enter the code generator of the data buffering device (for example, Mark 5B or Mark 5B +), which records signals on magnetic media and transmits them to the center of correlation data processing.

The main disadvantage of this system is the limited sensitivity of the radio interferometer due to the relatively narrow spectral bands of the recorded signals (usually 16 MHz or less and less often 32 MHz). With such bandwidths of video converters, the sensitivity of the radio interferometer is high enough only for large antennas of radio telescopes, and for such advanced VLBI systems created on small-sized (6-12 m) antennas, such ATPs are unsuitable.

In addition, a certain amount of time is spent on digital filtering and converting signal samples to FPGAs. Therefore, the samples of the quantized sequences entering the shaper of the data code of the recording device are delayed for this time relative to the moments of reading the samples in the ADC. Accordingly, the moment of input of 1PPS pulses forming the time scale into the data code generator is lagged by the same time. To take this time delay into account in the correlation processing of signals, one has to either shift or expand the correlation response search window.

The main objective of the invention is to expand the frequency band of the signal converted in the channel and increase the sensitivity of the radio interferometer. Additional goals are to eliminate the shift of the pulse sequences of the quantized signal relative to the recorded time scale. Another goal is to provide the possibility of mutual correlation of the signals recorded by different radio telescopes in case of mismatch of the directions of the signal spectra.

The main goal is achieved by the fact that in a system containing n signal conversion channels, each of which includes an input amplifier with a bandpass filter, an analog-to-digital converter connected to a read clock signal generator, and a first digital signal sample comparator connected to a RMS calculator the values of the signal samples, as well as the pulse sensor of the second seconds of the current time and the generator of the output data code connected to the output data buffering device, in each channel of signal generation, a w-channel demultiplexer is introduced, the corresponding inputs of which are connected to the aforementioned analog-to-digital converter, a calculator of the rms value of the signal samples and a clock signal generator, and the outputs are connected to digital signal sample comparators, (m-1) additional digital signal sample comparators connected to the calculator of the rms value of the samples and to the shaper of the output data code, and a frequency divider included between the generator ohm of the read clock signal and the clock inputs of all digital sample comparators.

Due to the introduction of a w-channel demultiplexer and an increase in the number of parallel comparators by a factor of t, the read speed of samples of the noise signal in the ADC is increased and the passband of the input filter, which limits the signal spectrum width, is expanded by the same amount. Expanding the spectra of the recorded signals by a factor of t increases the sensitivity of the radio interferometer by a factor of t at the same time of reception and accumulation of the signal, or by a factor of l / t reduces the necessary time of signal reception (for a given sensitivity).

Another goal (eliminating the shift of the output information sequences relative to the time scale specified by the second pulses) is achieved by the fact that the second pulse sensor is connected to the blocking inputs of the ADC in all channels of the SPS. In this case, the first sampling of the input signal that the ADC reads when the leading edge of the second pulse (1PPS signal) appears is sent to the 1st output of the w-channel demultiplexer and, accordingly, goes to the 1st digital comparator. The second sample of the signal is sent to the 2nd comparator and so on until the wth sample of the signal inclusive, after which the cycle of distribution of samples is repeated. Thus, by the ordinal number of the signal sample (and, accordingly, by the number of the digital comparator), the positions of the moments of reading the signal samples on the time scale determined by the primary second pulse generator are uniquely determined. This is preserved when generating a data output code in which the sequence of characters is not violated, for example, when using the VDIF format recommended for VLBI networks (see A.Whitney, M.Kettenis, C.Phillips, M.Sekido. VLBI Data Interchange Format (VDIF) // IVS 2010 General Meeting Proceeding, p. 192-196. Hobart. Australia. February 7-13. 2010).

Another goal is to provide the possibility of mutual correlation of signals received by different interferometer radio telescopes, if their spectra do not coincide, by the fact that switchable digital inverters (DIs) are installed at the inputs of digital comparators with odd serial numbers.

When the inverters are off, the spectrum of the pulse sequence at the channel output corresponds to the spectrum of the input noise signal, and when the inverters are on, the signs of the samples with odd serial numbers change in the sequence of signal samples taken from the ADC. This is equivalent to multiplying the digital sequence by the function (-G), where i is the serial number. Moreover, as is known from the theory of digital signal conversion, the spectrum of the output pulse sequence becomes inverted (inverse to the spectrum of the input signal). This allows all radio telescopes of the VLBI network using input receiving channels with different frequency conversion methods to establish the same direction of the spectra of the recorded signals, which is necessary to obtain a correlation response to the signal.

The figure shows a block diagram of the claimed utility model, where

indicated by:

1 ₁ , ..., 1 _n - signal conversion channels (total n channels);

2 - shaper output code data;

3 - device buffering and data transfer;

4 - pulse sensor seconds of the current time;

5 - clock signal generator (GSTCH) read signal samples;

6 - input amplifier with a bandpass filter;

7 - analog-to-digital Converter (ADC);

8 - w-channel demultiplexer;

9 - frequency divider;

10 - calculator rms values (RMS) of the samples of the signal;

11 _i , ... 11 _m - digital comparators of signal samples (with serial numbers from 1 to t);

12 - switchable digital inverter (total m / 2. Inverters in the channel with odd numbers).

Each channel 1 contains a series-connected input amplifier with a band-pass filter 6, ADC 7, a demultiplexer 8 and an SKK 10 calculator. Digital comparators 11 with even serial numbers are directly connected to the outputs of the demultiplexer 8, and with odd numbers through a switched inverter 12. The second digital inputs comparators 11 are connected to the output of the SKZ 10 computer, and the control (clocking) inputs are connected to the output of the frequency divider 9, which is connected to the GSTCH 5. To the GSTCH 5, the clocking inputs of the ADC 7 and demultiplexer 8 are also connected. Three A control input for the ADC 7 is connected to the second pulse sensor 4. The outputs of all digital comparators 11 are connected to the output data generator 2, the output of which is connected to the buffer device 3. The output of the data buffering device 3 is the output of the claimed utility model and is designed to be connected to a high-speed trunk data transmission lines (for example, to a fiber-optic line via a 10G Ethernet interface).

The inventive system is connected to the outputs of the channels of the radio astronomy receiving devices (RPU) and operates as follows. The high-frequency noise signals received by the antenna mixed with the intrinsic noise of the receiving system are converted to the working frequency band of the input amplifiers (for example, to the band 1-1.5 GHz), determined by the band-pass filter 6 and fed to the ADC 7, which reads the samples of the signal with the clock frequency Rsch on which the GSTCH 5 works. From the pulse sensor 6, which is usually used as the receiver of the GLONASS / GPS global navigation satellite system, pulses are sent to the ADC 7 trigger input, indicating the beginning of the next second World Time (the so-called 1PPS signal). When this pulse appears (on its leading edge), the first read signal sample is addressed to the 1st output of the demultiplexer 8 and then to the 1st digital comparator 111. The code of the received signal sample in the comparator is compared with the RMS code of the signal samples received from the calculator 10 As a result, a 2-bit code is generated (00,01,10 or 11), where the first character shows the sign of the signal sample, and the second indicates the excess (or not exceed) of the module of this sample compared to the RMS.

The next (second in order) sample of the signal undergoes the same procedure in the second digital comparator 11 ₂ , the third sample in the third comparator 11 _3, and so on, until the m-th sampling of the signal is completed. At this moment, m 2-bit codes are simultaneously copied to the output data code generator 2, and the cycle of the digital comparators 11 ₁ , ..., 11 _m is repeated. 2m-bit information words from each channel of the system enter the output code generator 2 with a data refresh rate of F _cph / m, which is set by a clock frequency divider 9. If it is necessary to invert the spectrum of the converted signal, inverters 12 are turned on. All channels of the ATP 1 ₁ ... 1 _n work the same and in parallel.

Shaper of the output data code 2 converts n streams of information 2m-bit words into a serial output stream of observation data in accordance with the VDIF format recommended for VLBI. The speed of the output data stream is ν = 2nF _sc . For example, with a bandwidth of the input filter of 500 MHz, you can take F _cf = 1024 MHz. Then the total speed of the data stream received from the 4-channel SPS (n = 4) will be 8.192 Gbit / s. The resulting data stream is written to the buffering device 3, from where it is read and transmitted to the center of correlation processing by FOCL in quasireal time. The inventive system can be performed on a modern element base. Input strip amplifiers with filters 6 and GSTCH 5 can be made in the form of integrated hybrid microassemblies. ADCs operating at frequencies up to 2-3 GHz are produced commercially in the form of microcircuits (for example, ADC081500). Digital comparators 11 ₁ , ..., 11 _m , SKZ 10 calculator, frequency divider 9 and inverters 12 can be formed on one programmable logic integrated circuit (FPGA), for example, XC6SLX100T, Spartan-6 or XC7K32T, Kintex-7. Demultiplexers are available in the form of microcircuits or are integrated into ADC microcircuits (for example, ADC081500). Demultiplexing signal samples can be done in FPGA. Embodiments of the demultiplexer 8 may be different depending on the number of channels m and the selected ADC and FPGA. The output data code generator 2 can also be performed on the FPGA, for example, on the XC7K32T FPGA, which has a built-in transceiver for transmitting the data stream to the buffering device 3. V As the latter, you can use, for example, the Mark 6 recording terminal, developed by Conduant.

According to the claimed utility model developed circuitry and software for FPGAs. The proposed technical solutions were tested on a 2-channel ATP mockup with 500 MHz channel bandwidths. Data streams with speeds of 2.048 Gbit / s from each channel were recorded in a digital buffering device and correlated with a computer equipped with a JTAG interface.

Claims (3)

1. A signal conversion and registration system for a radio astronomy interferometer, comprising n signal conversion channels, each of which includes an input signal bandpass filter, an analog-to-digital converter connected to a read clock signal generator, and a first digital signal sample comparator connected to a computer the rms value of the samples of the signal, as well as a pulse sensor of the second seconds of the current time and a shaper of the output data code connected to the output device data buffering, characterized in that an m-channel demultiplexer connected to the aforementioned analog-to-digital converter, a calculator of the rms value of the signal samples, and a clock read signal generator, (m-1) additional digital signal sample comparators, is introduced into each signal conversion channel, connected to the calculator of the rms value of the samples and to the data code generator, and a frequency divider connected between the read clock signal generator and clock inputs of all digital sample comparators. 2. The signal conversion and registration system according to claim 1, characterized in that the second pulse sensor is connected to the blocking inputs of the analog-to-digital converter in all channels of the signal conversion and registration system. 3. The signal conversion and registration system according to claim 1, characterized in that switchable digital inverters are installed at the inputs of digital comparators with odd serial numbers.