RU130463U1 - BROADBAND CHANNEL FOR CONVERSION OF SIGNALS FOR RADIO INTERFEROMETER - Google Patents

Abstract

1. A broadband signal conversion channel for a radio interferometer, comprising a serially connected input receiving-amplifying path, an analog-to-digital signal converter, a digital signal sample distributor, an m-channel amplitude quantizer of digital samples, a frame of observed data with a timer, and an output stream generating and transmitting device data, the calculator of the standard deviation of the samples of the signal connected to the distributor of samples and with the m-channel quantizer, and t also a control controller connected to a radio telescope computer, a second pulse synchronizer and a clock signal generator connected to an analog-to-digital converter, a signal sample distributor and a second pulse synchronizer, characterized in that an overhead information shaper is introduced connected to the observable frame shaper data and a control controller, an overflow pulse counter connected to a signal sample distributor and a control controller, and calculates An amplifier for the average value of signal samples connected to a sample distributor and to a zero correction input of an analog-to-digital signal converter, the control controller being connected to a gain control element of the receive-amplifier path. 2. The broadband channel according to claim 1, characterized in that a pulse delay device is introduced between the second pulse synchronizer and the timer of the imaging frame of the observed data.

Description

The utility model relates to radio astronomy and is intended for use on radio telescopes operating as part of ultra-long base radio interferometry complexes, which provide the most accurate angular, coordinate-time and ephemeris measurements and are widely used in basic scientific research and in solving applied problems of the national economy , for example, coordinate-temporal support of the country, maintaining the global satellite navigation system GLONASS, long-range space navigation predictions, earthquake and asteroid hazard predictions (see AMFinkelstein, A.V. Ipatov and S.G. Smolentsev Radio Interferometric Network “Quasar” - scientific tasks, technology and future // “Earth and the Universe” No. 4. 2004. P. 12-25; AMFinkelshtein et al. “Kvazar-KVO” radio interferometric network - the basic coordinate-time support system // Transactions of IPA RAS. Issue 13. St. Petersburg: “Science. 2005. P.104-138).

Radio interferometric signal conversion systems (SPS) are connected to the antenna of the radio telescope and provide amplification and separation (filtering) of signals in the specified frequency bands Δf, conversion of the selected signals into digital data streams that are recorded and then transmitted from all radio telescopes of the VLBI network to the center of correlation data processing . At present, for high-precision VLBI measurements, radio telescopes with large antennas are used (for example, with 32-meter antennas in the Quasar-KVO complex), which allows digital signal conversion at video frequencies with Δf≤32 MHz bands. Such a band is quite sufficient for the high sensitivity of a radio interferometer on large antennas. The most advanced ATP of this class include VLBI 4 multi-channel 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), and ATP of Russian production P1000 and P1002M (see A.V. Ipatov, N.E. Koltsov, L.V. Fedotov Radio Interferometric Terminal of the Badary Observatory // Instruments and Experimental Technique. 2009. No. 1. P. 52-57) 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. 5. S.60-66).

In connection with the increase in the volume of scientific research and applied problems solved by VLBI methods, in the developed countries abroad and in Russia, the development of a new generation of radio interferometers with high-speed antennas of small diameter (up to 13 m) is being developed, and to compensate for the loss of sensitivity (due to a decrease in the effective antenna area) ATP will be used with broadband (Δf≈0.5-1 GHz) channels of digital signal conversion. Unlike existing radio interferometers on large antennas, where the observation data is transmitted to the VSI-H VLB correlator, and the accompanying service information about the radio telescope, observation conditions, system channels and weather data are transmitted in a separate file (log-file), in new for radio interferometers on small antennas, a data stream should be generated in the VDIF (VLBI Date Interchange Format) format, the header of which should include all service information (see, for example, Alan R. Whitney. Wide-Bandwidth Digital Backend System for VLBI // Proc. of the 18 ^th European V LBI 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 closest in purpose and technical essence of the device (prototype) is the channel of the signal conversion system, presented in the patent for utility model No. 122810 dated 10/31/2011 "Signal conversion and registration system for radio astronomy interferometer".

The signal conversion channel in the known ATP (prototype) contains a path for amplifying and filtering the signals coming from the antenna, an analog-to-digital converter (ADC) connected by control inputs to a clock frequency generator (GSTCH) and to a second pulse generator, m-channel demultiplexer, meter standard deviation (RMS) of the signal samples, m-channel digital signal quantizer connected to the RMS calculator, a device for generating and transmitting a sequence of quantized signals (observation data ) to the data buffering device for transferring them further to the correlator of the radio interferometer. The channel of the system is controlled by the central computer of the radio telescope through the control controller integrated in the channel.

The noise signal, consisting of the received signal from a cosmic radiation source and the intrinsic noise of a radio telescope, is converted by the ADC into a sequence of digital samples with a clock frequency F _cf. This sequence is distributed over t quantization channels, each of which generates 2-bit codes with a clock frequency F _cf / m as a result of comparing the amplitudes of the signal samples with the previously calculated RMS value. The codes obtained in the quantizer channels in the form of 2m-bit words are copied with a clock frequency F _cf / m to a shaper of a serial data stream. Through the transceiver, the generated data stream is transmitted to the data buffering device for subsequent sending via the trunk line (for example, fiber optic) to the center of correlation data processing.

The well-known ATP channel (prototype) processes signals with wide (for example, 512 MHz) frequency bands and can be used in radio interferometers with small antennas. However, the well-known ATP does not provide complete (without the participation of a human operator) automation of VLBI observation processes and correlation processing of data in the VDIF format. This drawback is primarily due to the fact that the output stream of data coming from the channels of a known system contains only formatted data of the observation results, and the necessary related auxiliary information (data on the radio telescope, parameters and conditions of observations, meteorological conditions, etc.) is accumulated in the control computer of the radio telescope and is transmitted separately (log-file) similar to how the operating radio interferometers in VSI-H format work (see, for example, S.A. Grenkov, N.E. Koltsov, E.V. Nosov, L.V. . Fedotov Qi rovaya radiointerferometric system signal converting // Instruments and Experimental Techniques. 2010. №5. S.60-66).

In addition, during the VLBI observation session, due to the restructuring of the antenna from one cosmic radiation source to another and changes in its orientation relative to the Earth's surface, the intrinsic noise of the radio telescope can significantly (up to 2-3 times). In this case, the optimal operation mode of the ADC is violated and, as a result, the sensitivity may be unacceptably large due to the limitation of the input signals (during ADC overflow) or due to an increase in quantization noise when the working range of the ADC input voltages is not fully used. To avoid such loss of sensitivity of the radio telescope, the operator has to monitor signal levels and adjust the channel operating modes during the observation session, maintaining the RMSD σ of the input noise signal approximately equal to ΔU _max / 6, where ΔU _max is the permissible total voltage swing at the ADC input (from -U _max to + U _max ).

During the VLBI observation session, due to changes in the thermal mode of the ADC and the instabilities of the reference voltages, a zero level shift of the digital signal samples read by the ADC is possible. This leads to errors in the calculation of the standard deviation σ and, accordingly, to a shift in the thresholds of two-bit digital quantization of signals, which is also one of the reasons for the decrease in the sensitivity of the radio interferometer. Therefore, the operator has to periodically monitor the quality of the channel (for example, by calculating on the computer the number of intersections of threshold levels -σ, 0 and + σ with the quantized signal) and allow increased hardware sensitivity loss.

Another disadvantage of the known SPS channel is that the exact binding of the observational data to a single time scale of the radio telescope is achieved only when using such ADCs that have an integrated device for blocking and starting from external second pulses. An ADC chip with an integrated locking and triggering device can be easily selected for an ATP channel operating at frequencies below 1 GHz, but at frequencies above 1 GHz there are very few such ADCs and they do not always meet other requirements - the presence of built-in demultiplexers and dividers of clock frequency, bit depth, range input voltages. Most ADC microcircuits operating in the frequency range from 1 GHz to 2-2.5 GHz, which corresponds to the range of output intermediate frequencies of the developed receiving devices for advanced radio interferometers, do not have a blocking input.

The purpose of the claimed utility model is to provide the ability to fully automate the process of VLBI observations.

An additional goal is to ensure that the formatted observational data is linked to a single time scale of the radio telescope when the ADC does not have built-in blocking and triggering devices.

The main goal is achieved by the fact that into a broadband signal conversion channel containing a serially connected input receiving-amplifying path, an analog-to-digital signal converter, a digital signal sample distributor, an m-channel amplitude sample quantizer, a frame of observable data, and a device for generating and transmitting the output stream data with a timer, as well as a control controller connected to the computer of the radio telescope, second pulse synchronizer connected to the primary yes the time telescope of the radio telescope, the RMSE computer of the signal samples connected to the sample distributor, with the m-channel amplitude quantizer and to the control controller, and the clock signal generator connected to the analog-to-digital converter and to the signal sample distributor, service information shaper connected to the frame of the observed data and with the control controller, an overflow pulse counter connected to the distributor of signal samples and with the control controller, and calculates An amplifier of the average value of the samples connected to the sample distributor and to the zero correction input of the analog-to-digital converter, the control controller being connected to the gain control element of the receive-amplifier path.

Such a channel eliminates the need for the participation of a human operator in the VLBI process and provides full automation of the radio interferometer. The service information coming from the radio telescope computer through the channel control controller is formatted and entered as a header into the VDIF standard data format, and then, together with the observation data, is transmitted to the VLBI correlator. At the same time, the optimum operation mode of the ADC is automatically maintained, in which the loss of sensitivity of the radio interferometer is minimal. Before observing each radiation source, the relative number (percentage) of overflows of the code samples of the signal is calculated and the result is transmitted to the control computer. If the relative number of overflows is outside the permissible limits (for example, 0.001-0.003), the computer through the channel control controller gives a command to adjust the gain control element (attenuator) in the receive-amplifier channel.

At the same time, the average voltage U _{cf of the} signal samples is calculated and, if the result differs from 0 more than the acceptable value equal to the correction step for a given specific ADC (for example, 0.1 steps of signal quantization in the ADC), a zero-level adjustment code in the ADC is generated. These adjustments are carried out before observing each source. After adjustment, the channel converts the signal received from the radiation source in the optimal mode (with minimal hardware loss of sensitivity).

An additional goal is achieved by the fact that between the pulse synchronizer of the seconds and the timer of the imaging frame of the observed data, a pulse delay device is installed. The second pulse synchronizer, triggered by pulses from a primary time sensor (for example, from a GPS / GLONASS receiver) combines the second pulses along the edges with the clock meander with which the signal quantizers and the imager of the observation data work, i.e. generates stable pulses of time stamps, usually called the 1PPS (One pulse per second) signal. Each 1PPS pulse is delayed by the time equal to the time taken to pass the signal sampling from the ADC to the output of the data frame former, as a result of which the timer time scale in the observer data formatter is shifted by the same time. As a result, the signal sampling, which appeared at the moment of arrival of the pulse of the next second, falls into the initial bit of the data stream in VDIF format. Due to this, the VDIF observations are uniquely determined on a single time scale of the radio telescope, which is necessary for the correct determination of the delays of the received signal based on the radio interferometer.

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

1 - channel signal conversion;

2 - input receiving-amplifying path;

3 - gain control element (attenuator);

4 - analog-to-digital signal converter (ADC);

5 - m-channel distributor of digital signal samples;

6 - m-channel amplitude quantizer of digital samples;

7 - frame former observable data;

8 - a device for generating and transmitting an output data stream;

9 - shaper service information;

10 - channel control controller;

11 - pulse counter overflow ADC;

12 - calculator of the average value of the signal samples;

13 - second pulse synchronizer (1PPS signals);

14 - device delay pulses of seconds;

15 - channel timer;

16 - clock signal generator (GSTCH);

17 - the primary sensor of the time scale of the radio telescope (for example, a receiver of satellite navigation systems GPS / GLONASS);

18 - computer control radio telescope;

19 is a calculator of standard deviation of the samples of the signal.

The input receiving-amplifying path 2, ADC 4, the distributor of samples 5, the amplitude quantizer of samples 6, the imager of the frames of the observed data 7 and the device for generating and transmitting the output data stream 8 are connected in series. The input of path 2 is the input of channel 1, and the output of device 8 is the output of the channel. The output of the distributor of samples 5 is connected to the calculator RMS 19, also connected to the m-channel quantizer 6 and to the control controller 10, an overflow pulse counter 11, connected to the output from the controller 10, and a calculator of the average value of the samples 12, connected to the output from the ADC 4 by the correction input zero level sample codes. The clock inputs of the ADC 4 and the sample distributor 5 are connected to the output of the GSTCH 16. Another output of the GSTCH 16 is connected to the clock input of the amplitude quantizer 6 and to the pulse synchronizer of seconds 13, which is connected to the primary sensor of the time scale of the radio telescope 17. A device is connected to the output of the synchronizer 13. delay 14, the output of which is connected to the timer 15 of the data frame shaper 7. A service information shaper 9 connected to the control controller 10 is also connected to the shaper 7. The controller 10 is connected ose from radio telescope control computer 18 and a gain control element (attenuator) 2 3 tract.

The claimed device operates as follows. The ADC 4, with a clock frequency F received from the GSTCH 16, converts the amplified input noise signal into n-bit codes of digital samples of the signal, which contain 1 bit of the voltage sign, n-2 bits of the voltage amplitude and 1 bit of the ADC overflow. The codes of the signal samples through the distributor 5 go to the RMS computer 19 and to the m-channel amplitude quantizer 6, which, with a clock frequency of F / m, generates 2m-bit words corresponding to 2-bit amplitude quantization of the signal voltage at threshold levels U <-σ, −σ≤U <0, 0≤U <σ and σ≤U, where σ is the calculated value of the standard deviation. In this part, the claimed device works in the same way as a known device (prototype). The resulting 2m-bit words are copied to the observational data frame former 7, which works in the VDIF format recommended for promising radio interferometers with extra-long bases.

Shaper 7 is started by the timer 15 built into it when a time stamp pulse (1PPS signal) is received, which is generated by the pulse synchronizer of seconds 13 and is delayed by the device 14 for a time equal to the passage of the signal sampling from the ADC input 4 to the output of the shaper 7.

Due to this, the first two bits of the initial word of the initial data frame will refer to the digital sample read by the ADC 4 at the moment of the appearance of the 1PPS second pulse. This provides a rigid and unambiguous binding of data to the time scale of the radio telescope.

At the same time, a data frame header is generated in the shaper 9, containing service information coming from the computer of the radio telescope 18 through the controller 10. The generated service data is transmitted to the shaper 7, where it is entered into the header of the data frame in the VDIF format. The generated frames of the VDIF format by the device 8 are converted into a serial data stream and transmitted to the data buffering device on the radio telescope for subsequent transmission to the center of correlation processing.

Digital samples of the signal by the distributor 5 are also transmitted to the calculator of the average value U _{cp of the} digital samples of the signal and to the counter 11 of the ADC overflows. The counter 11 calculates the proportion (percentage) of overflows in the total set of samples for the set time and transfers the result to the controller 10. If the percentage of overflows falls outside the set limits (for example, 0.001-0.003), then the controller 10 gives the adjustment code of the attenuator 3 in the amplifier path 2, providing thereby the optimal level of the noise signal at the input of the ADC 4.

The average value calculator U _{cf of} digital samples 12 in the case of deviations of U _cp from zero is greater than the permissible value (for example, more than 0.1 of the low-order price of the voltage code) generates a command to offset the zero level of the ADC 4, thereby eliminating errors in the calculation of the standard deviation σ and , accordingly, providing high quality amplitude quantization of the signals in the device 6.

All adjustments are carried out automatically according to a given program.

The device can be implemented on ADC chips (e.g., National Semiconductor's ADC081500), programmable logic integrated circuits (e.g., XC6SLX100T, Spartan-6 or XC7K32T, Kintex-7 Xilinx) and other general-purpose chips. Input amplifier path 2 and GSTCH 16 can be made in the form of integrated hybrid microassemblies.

According to the claimed device, two experimental samples were manufactured and tested in the laboratory and on RT-32 radio telescopes. The development of prototypes has begun.

Claims (2)

1. A broadband signal conversion channel for a radio interferometer, comprising a serially connected input receiving-amplifying path, an analog-to-digital signal converter, a digital signal sample distributor, an m-channel amplitude quantizer of digital samples, a frame of observed data with a timer, and an output stream generating and transmitting device data, the calculator of the standard deviation of the samples of the signal connected to the distributor of samples and with the m-channel quantizer, and t also a control controller connected to a radio telescope computer, a second pulse synchronizer and a clock signal generator connected to an analog-to-digital converter, a signal sample distributor and a second pulse synchronizer, characterized in that an overhead information shaper is introduced connected to the observable frame shaper data and a control controller, an overflow pulse counter connected to a signal sample distributor and a control controller, and calculates An amplifier of the average value of the signal samples connected to the sample distributor and to the zero correction input of the analog-to-digital signal converter, the control controller being connected to the gain control element of the receive-amplifier path. 2. The broadband channel according to claim 1, characterized in that a pulse delay device is introduced between the second pulse synchronizer and the timer of the driver of the frames of the observed data.

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