RU196816U1 - SPACE RADIO SYSTEM FOR REGISTRATION OF SPACE RADIO EMISSIONS - Google Patents

Abstract

The utility model relates to radio astronomy technology, and more specifically to digital systems for recording cosmic radio emission in spectral lines. The system contains a broadband directional coupler through which lateral arm noise pilot signals from a modulated noise generator are input, a receiver with a wide passband B, analog-to-digital broadband signal converter, demultiplexer, digital signal extraction device with a relatively narrow spectrum bandwidth ΔF, narrowband computer pektrov power narrowband signal and a dedicated computer. The signal spectrum is calculated by the fast Fourier transform method and by the amplitudes using noise pilot signals. In order to eliminate errors in calculating the amplitudes of the signal spectrum associated with the unevenness and instability of the power spectrum of noise pilot signals in the reception band B, an additional broadband signal power spectrum calculator, a switchable two-channel spectrum storage device, and a spectral subtraction device connected to the output by the computer are connected to the output of the demultiplexer . The switch in the two-channel spectral storage device is controlled by the same meander generator that controls the noise pilot signal generator.The technical result in the implementation of the claimed solution is to increase the accuracy of measuring the power spectra and noise temperatures of the received radio emission, as well as reducing the requirements for the spectral characteristics of the noise generator used. 1 ill.

Description

The utility model relates to radio astronomy technology, and more specifically, to digital systems for recording cosmic radio emission in spectral lines.

A modern system for recording cosmic radio emission in spectral lines usually contains a radio astronomy receiving device (RPU) with a wide passband B ₀ , a video converter that tunes in the frequency band 0 ÷ B ₀ , selects and converts the studied narrow-band signal to video frequencies (ΔF≤32 MHz), and a high resolution frequency spectrometer. Various spectrometric systems (filter, acousto-optic, autocorrelation) are used in radio astronomy, but in studies in the ranges of decimeter and centimeter waves, the most accurate results are obtained by the use of spectrometers operating on the basis of the fast Fourier transform (FFT). The best samples include a system for recording radio emission in spectral lines used on RT-32 radio telescopes (see patent RU 64386 U1, IPC G01R 23/18, G01R 23/16, published on June 27, 2007, Bull. No. 18). The spectrometer of this system contains an analog video converter emitting a signal with a ΔF band, an FFT calculator of the power spectra of the extracted signal, which is generated in a programmable logic integrated circuit (FPGA), and a computer that records the power spectrum of the radiation under study. The amplitudes of the calculated spectrum are calibrated using noise pulses (pilot signals) with a small pre-measured noise temperature, which are introduced by a modulated noise generator (GS) into the broadband receiving channel (see patent RU 2316775 C1, IPC G01R 23/18, publ. 10.02. 2008, Bull. No. 4).

On a new generation of small radio telescopes, for example, on RT-13, systems are used that digitize broadband intermediate frequency (IF) signals with a band of ₀ to 1 GHz (see patents RU 101842 U1, IPC G01R 21/33, publ. 27.01. 2011, Bull. No. 3, or RU 166692 U1, IPC H03D 7/00, G01R 31/28, G01R 23/16, Н04В 17/21, publ. 12/10/2016, Bull. No. 34, or RU 176177 U1, IPC H03D 7/00, published on January 11, 2018, Bull. No. 2). In such systems, the studied signal with a relatively narrow band ΔF is extracted from the broadband (high-speed) IF signal by a digital device (see patent RU 175721 U1, IPC H03D 7/00, published on December 15, 2017, Bull. No. 35). The power spectrum of the extracted signal with a relatively narrow band ΔF can be measured with a high resolution narrow-band spectrometer made according to the scheme proposed in patent RU 64386 U1.

By the totality of the features closest to the claimed system (prototype) is the system proposed in patent RU 175721 U1 containing a high-speed analog-to-digital converter (ADC), a demultiplexer and a device for digital extraction of a narrow-band signal assembled on an FPGA, as well as a narrow-band spectrometer of video frequency signals, made according to proposed in the patent RU 64386 U1 scheme. The prototype circuit contains a serially connected broadband directional coupler connected by a side shoulder with a modulated GS, an RPU channel with a wide passband B ₀ , a high-speed (broadband) ADC, a demultiplexer, a digital narrow-band signal extraction device, and a spectrometer. A narrowband signal extraction device is made on the FPGA and contains a module of polyphase filters (PFF) and digital video converters (CVC). The spectrometer is composed of a narrowband power spectral computer (HSR) formed in the FPGA and a computer. The synchronizing output of the narrow-band high-speed line through the meander generator is connected to the control (modulating) input of the power supply.

A spectrometer operating in the video frequency band (ΔF≤32 MHz) calculates in a conveyor way (without loss of radio signal reception time) the signal power spectra in the ΔF analysis band with a resolution of w = ΔF / N, where N is the number of discrete frequencies in the calculated spectrum. The meander, which modulates (turns on / off) the GS, is synchronized with the cycles of spectrum calculation. At a given time interval τ, the spectra calculated for different half-periods of the GS modulation are separately accumulated and averaged. Based on the obtained averaged spectra, taking into account the temperature value T _{n of} the noise pulses introduced into the RPU channel from the power supply, the amplitudes P _{si of the} components of the power spectrum and noise temperatures T _{si of the} radio emission received at the frequencies ƒ _si (i = 1, ..., N - discrete frequency serial number). The calculation formulas are given in patent RU 2316775 C1. The nominal value of T _n used in the calculations as a scaling factor is preliminarily measured by a radiometer and is the average noise temperature of the pilot pulses in the passband of the receiving channel.

The accuracy of determining the amplitudes P _si and T _{si of the} spectral components of the signal under study directly depends on how accurately the nominal value of the noise temperature T _n corresponds to the true value T _{ni of} this temperature at a frequency ƒ _si . Therefore, very stringent requirements are imposed on the GS for the stability and uniformity of the power spectrum of noise pulses in a wide frequency band B ₀ , which are very difficult to fulfill in practice. Widely used GS on avalanche-span diodes, for example, usually have an uneven power spectrum in the frequency band B ₀ ≈ 0.5 ÷ 1 GHz within 3 ÷ 4 dB. It may affect, although to a lesser extent, the uneven transmission coefficient of the broadband directional coupler used to connect the power supply. In addition, the values of T _ni may vary due to insufficient stability of the power of the mains with changes in ambient temperature and voltage (or current) power supply. Thus, the temperatures T _ni of noise pulses introduced into the RPM during the observation of signals at different frequencies can significantly (up to 2–3 times) differ from the nominal value of T _n .

Any deviations of the values of T _ni from the nominal value of T _n lead to additional errors when measuring the amplitudes of the spectral components of the investigated radio emission. This limits the possibility of studying small non-stationary radio emissions of the observed source. When registering radio emission in two orthogonal polarizations of the waves (linear or circular), an additional measurement error appears due to the unequal power spectra of the noise pulses in the two two channels of the RPU containing their GS.

The purpose of the claimed utility model is to increase the accuracy of measuring the power spectra and noise temperatures of the received radio emission, as well as to reduce the requirements for the spectral characteristics of the used GS.

This goal is achieved by the fact that in the registration system containing a serially connected broadband directional coupler connected by a lateral shoulder to a modulated GS, a broadband RPU, a high-speed ADC, a demultiplexer, a digital narrow-band signal extraction device, a narrow-band power spectrum calculator (BCM-U) and a computer, as well as a meander generator connected to the clocking output of the BCM-U computer and to the modulating input of the main oscillator, additionally connected to the output of the said demultiplexer no calculator connected broadband spectra signal strength (VSM-III), switchable dual drive spectra and subtraction device coupled to said computer output, the control input of the switch in dual storage spectra connected to the output of said square wave generator. Here, simultaneously with the calculation of the power spectra of the studied narrow-band signal at a frequency ƒ _si, the power and noise temperature spectra of the pulses introduced into the RPM are calculated in a wide band of intermediate frequencies (IF) of the receiving device. In this case, for the amplitude calibration of the signal spectrum, it is not the nominal value of the noise temperature T _n that is used, but the true value of the noise temperature T _ni for the frequency ƒ _si , which is determined by the calculated broadband power spectrum of the noise pulses introduced into the RPU channel. This eliminates errors in determining the amplitudes of the spectral components of the received radio emission, which occur when the deviations of the real noise temperatures T _ni from the average value of T _n .

The figure shows a diagram of the inventive system for recording space radio emission in spectral lines. It is indicated here:

1 - antenna feed;

2 - directional coupler;

3 - channel radio receiving device (RPU) with a wide passband In ₀ ;

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

5 - demultiplexer;

6 is a digital signal extraction device with a relatively narrow band ΔF;

7 - a transmitter of power spectra of a narrow-band signal (BCM-U);

8 - computer;

9 - meander generator;

10 - modulated noise generator (GS);

11 - calculator power spectra of a broadband signal (BCM-W);

12 - switchable dual-channel storage of broadband spectra;

13 - calculator of the difference of the spectra.

Antenna irradiator 1, directional coupler 2, RPU 3, ADC 4, demultiplexer 5, digital narrow-band signal extraction device 6, narrow-band signal power calculator 7, and computer 8 are connected in series. The output of the synchronizing pulses of the BCM-U 7 power spectral calculator is connected to the meander generator 9, which is connected by the output to the control input GSh 10 and to the control input of the switch in the dual-channel spectral storage 12. The output GS 10 is connected to the side arm of the directional coupler 2. To the output of the demultiplexer 5 connected in series are the VSM-U 11 broadband signal power spectral calculator, a switchable dual-channel broadband spectral storage device 12, and a spectral difference calculator 13 connected th output to a computer 8. The control input of the two-channel switch drive broadband spectra 12 connected to the output square wave generator 9.

The digital signal registration system, connected to the standard RPU of the radio telescope, can be performed on ADC and FPGA chips. The digital device for isolating narrowband signal 6 is performed on the FPGA according to the well-known scheme (see patent RU 175721 U1), where a polyphase filter module (PFF) and a frequency-tunable digital video converter (CVC) with a passband ΔF are used. The power spectrum calculator BCM-U 7 is also made according to the known scheme (patent RU 64386 U1). It contains an FFT spectral calculator on an FPGA with a two-channel spectral storage device and with a communication device with a computer 8. The BCM-W 11 broadband signal power spectra calculator, containing several parallel-working FFT spectrum calculators and an output broadband spectrum shaper, are assembled according to the well-known scheme considered in the description of patent RU 101842 U1. The dual-channel storage device for broadband spectra 12, having an input channel selector, is similar in structure and function to a similar device as part of a narrow-band spectrum calculator BCM-U 7.

The mixture of the radio signal received by the antenna, the intrinsic noise of the radio telescope in the B ₀ band and the noise pulses introduced into the RPU channel is fed to the ADC 4, which operates with the signal sampling frequency F _D = 2B ₀ . The obtained high-speed digital signal through a demultiplexer 5 is input to a narrow-band signal extraction device 6 and to a broadband calculator BCM-Ш 11. In a device 6 containing a PFF and CVC module, a narrow-band signal is extracted from a digital signal with a band of ₀ , the spectrum of which occupies a frequency band of 0 ÷ F. The analysis band ΔF is set approximately twice as wide as the spectrum of the studied radio signal, since for the amplitude calibration of the spectrum of the received radio signal, sections are required that are free of this signal (see patent RU 2316775 C1).

In VSM-U 7, the instantaneous power spectra of the narrow-band signal p (F _i ) are calculated and accumulated by the FFT method using the FFT method, where F _i is the frequency of the calculated spectrum that uniquely determines the frequency ƒ _{si of the} received radio signal. At the end of the calculation of the next spectra, the device 6 generates pulses that synchronize the operation of the meander generator 8 and the modulation of the noise generator 9. The spectra are calculated and accumulated over a given time interval τ separately for different half-periods of modulation GS 10 (when noise pulses are introduced into the channel RPU 3 and at their absence). The signal power spectrum P _si (F _i ) averaged over the time interval t is recorded by computer 8. The FPGA resources used in the BCM-U 7 limit the number of spectral components N of the calculated spectrum and the resolution w = ΔF / N, but at ΔF≤32 MHz the resolution necessary for the study (w≈0.1 ÷ 1 kHz) can be obtained even when using inexpensive FPGAs of the 4th or 5th generation.

In the VSM-Sh 11 broadband computer, the instantaneous power spectra of the broadband digital signal coming from the demultiplexer 5 are calculated by the conveyor method. The broadband spectra calculated by the conveyor method are transmitted to a switched dual-channel storage device of the broadband spectra 12, where the spectra obtained for different half-periods of modulation 10 are separately accumulated and averaged. (with the introduction of noise pulses in the RPU and in the absence of them). This provides an input switch in the drive 12, which is controlled by the meander generator 9. As a result of subtracting the accumulated spectra in the device 13, a broadband power spectrum P _nr (F _r ) of noise pulses introduced into the RPU is formed, where F _r is the discrete frequency with serial number r in the broadband spectrum. The power spectrum P _nr (F _r ) is recalculated by computer 8 into the spectrum of noise temperatures T _nr (ƒ _r ), pilot signals (pulses) introduced into the RPU channel from the power supply. The requirements on the number of spectral components M of the calculated broadband spectrum and on the resolving power W = B ₀ / M in this case can be reduced (for example, to W ≈ 1 MHz), since the power of noise pulses in the B ₀ band usually changes in waves and smoothly, without sudden changes.

Using the signal power spectrum P _si (F _i ) obtained at BCM-U 7, the spectrum of noise temperatures T _ni (ƒ _si ) of the received radio signal is calculated. The amplitudes of the spectral components are calculated according to the method proposed in patent RU 2316775 C1, but in the considered model, instead of the average (nominal) value T _{n of the} noise temperature of the pilot signals, the calculated values of T _nr are accepted for the frequencies ƒ _nr closest to the frequencies ƒ _{si of the} studied radio emission. As a result, errors are eliminated in calculating the amplitudes of the spectrum of the recorded signal, which are associated with the non-uniformity of the power spectrum of the power supply in the reception band B ₀ and with the instability of this power.

According to the claimed utility model, a preliminary technical design with the manufacture of a breadboard model has been completed, and breadboard tests have been carried out, confirming the effectiveness of the proposed solution. As shown by test observations of radio emission sources in spectral lines, the scatter of the measured amplitudes of the spectral components decreased by about an order of magnitude (from 20–30% to 2.2%).

Claims (1)

A system for recording cosmic radio emission in spectral lines, comprising a series-connected broadband directional coupler connected to the side shoulder with a modulated noise generator, a broadband receiver, an analog-to-digital converter, a demultiplexer, a digital narrow-band signal extraction device and a narrow-band power spectrum calculator with computer output, and also a meander generator connected to the clock output of the narrow-band power spectrum calculator and to the mode a noise generator input, characterized in that to the output of said demultiplexer there are connected additionally serially connected broadband signal power spectral calculator, a switched two-channel spectral storage device and a spectral subtraction device configured to be connected to a computer, the switch control input in a two-channel spectrum storage device being connected to the output said meander generator.

Images