SU1721534A1 - Spectrum acoustic-optical analyzer - Google Patents

Abstract

This invention relates to a radio measuring technique. The purpose of the invention is to increase noise immunity and selectivity. The analyzer contains laser 1, collimator 2, Bragg cells 3, lenses 4. arrays of photodetectors 5, visual indication units 6, receiving antenna 7, mixer 8, local oscillator 21, intermediate amplifier 9

Description

WITH

with

Vj

Yu

ate

SA)

four

frequencies, multipliers 10, and band-pass filters 11. Amplifier 12 of intermediate frequency, phase shifter 13 by 90 °, adder

The invention relates to a radio metering technique and can be used to visually analyze the spectrum of the signals under study and determine the type of modulation.

Acousto-optic spectrum analyzers are known.

Closest to the present invention is an acoustic spectrum analyzer that provides a detailed analysis of the spectrum and a visual determination of the type of modulation of the received signal. This is achieved by using, as informative features, the width of the spectrum and changes in its structure when the phase of the received signal is multiplied by two, four and eight.

The disadvantages of this spectrum analyzer are low noise immunity and selectivity. This is explained by the fact that the same intermediate frequency value can be obtained by receiving signals at two frequencies fc and. fs i

fnp f with - f g and fnp fg - fa.

Therefore, if the tuning frequency fc is taken as the main reception channel, then along with it there will be a mirror reception channel, the frequency fs of which differs from the frequency fc by 2fnp and is located symmetrically (mirror) relative to the frequency of the local oscillator fr (Fig. 5). The conversion in the image receive channel occurs with the same CRC conversion coefficient as in the main channel. Therefore, it most significantly affects the selectivity and noise immunity of the spectrum analyzer.

In addition to the mirror, there are other additional (combinational) reception channels, the frequency of which can be determined from the following equality:

 gp g, 1,

 + -fnp,

where m, n are integers.

The most harmful combinational channels of reception are the channels formed when the carrier frequency of the received signal interacts with the second harmonic of the local oscillator frequency, since the sensitivity of these channels is close to the sensitivity, multiplier 15, narrowband filter 16, amplitude detector 17, key 18, phase shifter 19 by 90 ° and mixer 20. 5 Il.

main channel reception. So, with m 2 and n 1, the two frequencies for the combination signals correspond to the frequencies fki 2fr - fnp and fk2 2fr + fnp.

The presence of spurious signals (interference), received by the mirror and combinational channels, leads to a decrease in noise immunity and selectivity of the spectrum analyzer.

0 The aim of the invention is to increase noise immunity and selectivity.

The goal is achieved by introducing a second mixer into the device,

5 second intermediate frequency amplifier, two phase shifters at 90 °, adder, fourth multiplier, narrowband filter, amplitude detector and key, with the first inputs of the second mixer and the fourth multiplier connected to the receiving antenna, the second input of the second mixer through the first phase shifter at 90 ° connected to the second output of the local oscillator, and the output through a series-connected 5 second intermediate frequency amplifier and the second phase shifter through 90 ° to the second input of the adder, the first input of which is connected to the output of the first of intermediate frequency amplifier, and the output - to

0 to the second input of the fourth multiplier and the first input of the key, the output of which is connected to the inputs of the first multiplier and the piezoelectric transducer of the first Bragg cell, and the second input through

5 serially connected narrowband filter and amplitude detector - with the output of the fourth multiplier,

FIG. 1 shows the structural scheme of the proposed spectrum analyzer; in fig. 2 0 oscillograms on the display unit screens; in fig. 3 - mutual arrangement of symbol frequencies of signals with multiple frequency shift keying; in fig. 4 - the law of phase variation of the frequency-manipulated signal; in fig. 5 is a frequency diagram illustrating the principle of forming additional (mirror and combination) reception channels.

Acousto-optical spectrum analyzer

0 contains a series of optically coupled laser 1, collimator 2 and cell

Bragg 3, in the diffracted beam of which a lens 4 and a matrix of photodetectors 5 are sequentially installed in its focal plane, is electrically connected to block 6 of a visual indication of the spectrum. At the same time, along the non-diffracted Bragg beam in the first cell, Bragg cells 3 (3.1–3.3) are located; in the course of the Bragg beam 3 (3.1–3.3) beam diffracted in each of the cells, the lens 4 (4.1–4.3) is sequentially installed and located in its a focal plane matrix of photodetectors 5 (5.1-5.3); an electrical output connected to block 6 (6.1-6.3) of a visual indication of the spectrum. A mixer 8 is serially connected to the output of the receiving antenna 7, the second input of which is connected to the output of the local oscillator 21, the intermediate frequency amplifier 9, the adder 14, the key 18, the multiplier 10.1, the band-pass filter 11.1, the multiplier 10.2, the band-pass filter 11.2, the multiplier 10.3 and the band pass filter 11.3. A mixer 20 is connected in series to the output of a receiving antenna 7. A second input of which is connected through a phase shifter 19 to a second input of a local oscillator 21, an intermediate frequency amplifier 12 and a phase shifter 13 of 90 °, the output of which is connected to a second input of an adder 14. To the output of a receiving antenna 7 are connected in series to the multiplier 15, the second input of which is connected to the output of the adder 14, narrowband filter 16 and the amplitude detector 17. The output of which is connected to the second input of the key 18. The output of the bandpass filter 11.1 (11.2, 11.3) is connected to the piezo Bragg's electric cell transducer 3.1 (3.2,3.3),

Acousto-optical spectrum analyzer works as follows.

Received signal, for example, with phase shift keying (FMN)

Uc (t.) Uc cos 2 n fc t +

t9 (t) + (pel 0 t t Ј Tc. where Uc, fc. Tc, pc is the amplitude, carrier frequency, duration, and initial phase;

 (t) is the manipulated component of the phase, which reflects the law of phase manipulation, and (pt (t) const, for k rp t (k-f-1) Th, and may vary abruptly at tk rn, i.e. between elementary parcels k 1, 2 ,. „, N-1, where, N is the duration and the number of elementary parcels from which the signal Tc (Tc N tp) is composed from the output of the receiving antenna 7 simultaneously arrives at the first inputs of mixers 8 and 20 and multiply5

0

five

0

five

0

five

0

five

0

bodies 15. The second input voltage of the local oscillator 21 is applied to the second input of the mixer 8

Ur, (t) Ur cos (2 l fr t + fb), where Vr, fr, pr is the amplitude, frequency, and initial phase of the local oscillator voltage.

A voltage is applied to the second input of the mixer 20 from the output of the phase shifter 19 by 90 °.

Urz (t) Ur cos (2 l fr t + (pf + 90 °).

At the outputs of the mixers 8 and 20, voltage combinations are generated. Amplifiers 9 and 12 separate the intermediate voltage (difference) frequency Unp (t) Unp, cos 2jrfnptH-pk (t) +

Unpjt) - Unpt COS 27rfnpt + k (t) + - 90 °,

where Unp, 1/2 ki Vc Vr, 0 0 t «Tc;

ki is the transfer coefficient of the mixers ;,

fnp fc - fr - intermediate frequency;

ppr - (fie - intermediate initial phase.

. The voltage Unp2 (t) from the output of the intermediate frequency amplifier 12 is fed to the input of the phase shifter 13 by 90 °, the output of which is the voltage

UnPi (t) Unp (cos 2 fnp t + pk (t) +

+ (RPR - 90 ° + 90 ° Unp, cos 2 n fnp t +

+ pk (t) + pnpl 0 1 “TC.

The voltages Unp, (t) and Unpa (t) are fed to the two inputs of the adder 14, the output of which is the voltage

U U COS 2 П fnp + pk (t) + + fnp,,.

rfleVS) 2 VnPr

The voltage (t) from the output of the adder 14 enters the second input of the multiplier 15, the output of which is the voltage

Ui (t) Vi cos (2 n frt +) +

+ Vr (2fc-fr) t +

+. Pr,,

rfleUi l 2UcUt;

k2 is the multiplier transfer coefficient.

The tuning frequency fn of the narrowband filter 16 is chosen equal to the frequency fr of the local oscillator 21 (fH fr). Therefore, the harmonic voltage falls into the passband of the narrowband filter 16

U2 (t) Ui: cos (2n: frt + pr),. About t gc. which, after detection in the amplitude detector 17, enters the control input of the key 18 and opens it. Key 18 in its original state is always closed. In this case, the voltage from the output of the adder 14 through the public key 18 is supplied to the two inputs of the multiplier 10 and to the Bragg cell 3, where the signal is converted into an acoustic oscillation.

A beam of light from laser 1, collimated by collimator 2, passes through a Bragg cell 3 (3.1–3.3) and diffracts on acoustic oscillations excited by a signal. In this case, only about one tenth of the radiation source beam diffracts. In the path of the diffracted part of the light beam, lenses 4 (4.1-4.3) are installed. In the focal planes of these lenses, which form the spatial spectrum of the received signal, matrices of photodetectors 5 (5.1-5.3) are installed. Moreover, each resolution element of the analyzed frequency range corresponds to its own photodetector.

The Bragg cell 3 (3.1–3.3) consists of a sound conductor and a hypersound piezoelectric plate made of lithium niobate crystal, respectively, X and Y –35 ° cut. This provides automatic adjustment of the Bragg angle and cell operation in a wide frequency range. Oscillographic indicators can be used as display units 6 (6.1-6.3).

If a complex signal with a single PMNK (p (i) 0, l) arrives at the spectrum analyzer input, then, after frequency conversion and summation through the public key 18, it arrives at the Bragg cell 3 and at the two inputs of the multiplier 10, at the output of which a harmonic living

U3 (t) U3COS 4rtfnpt +

+, where U3 1/2 k2 and.

Since 2 pk (t) is 0.2, then the phase minipulation is already absent in the indicated voltage. The voltage Us (t) is separated by a band-pass filter 11 and is fed to a Bragg cell 3 and to the two inputs of a multiplier 10, the output of which forms a harmonic voltage

U4 (t) U4COS (8jrfnpt +

+) Q & ЈTS,. where U4 1/2k2 uf; :

This voltage is separated by a band-pass filter 11 and enters the Bragg cell 3 and two turns of the multiplier 10, at the output of which a harmonic voltage is generated

Us (t) Us cos (16 n fnp t +

+), where Us-1/2 k2 U4.

This voltage is allocated by a bandpass filter 1.1 and is fed to a Bragg cell 3. The spectral width A fc of the QPSK-2 signal is determined by the duration of the elementary premises (Lfc 1 / ti). Whereas the width of the spectrum

the second A fc, the fourth A U and the eighth A fs harmonics are determined by the duration of the signal Tc (A f2 A f4 - A fe 1 / Tc). Consequently, when the phase is multiplied by two, four and eight, the QPSK-2 spectrum of the signal collapses 8 N times (d / d A | N) and transforms into single spectral components. This circumstance is a sign of recognition of the QPSK-2 signal. The spectra of the received FMN-2 signal and its harmonics (Fig. 2) are visually observed on the screens of the indicators 6 (6.1,

6.2 and 6.3) respectively.

If the FMN-4 signal, pk (t) 0, yy / 2, g, 3/2 1 arrives at the spectrum analyzer input, then the QPS-2 signal pk (t) 0,, 1 L, 3 is generated at the output of the band-pass filter 11. l, and at the output of bandpass filters 11.2 and 11.3

corresponding harmonic voltages U4 (t) and Us (t) are generated. In this case, the spectra of FMN-4 and FMN-2 signals are observed on the screen of indicators 6 and 6.1, and on the screens of indicators 6.2 and 6.3 are observed

single spectral components (Fig. 26).

If the device receives the QPSK-8 signal pk (t) 0. l / Al 11, 3/4 l: then at the outputs of the band-pass filters 11.1 and 11.2

FMN-4 and FMN-2 signals are generated, and harmonic voltage Us (t) is formed at the output of the band-pass filter 11.3. In this case, on the screens of indicators 6, 6.1, 6.2 and

6.3 the spectra of FMN-8, FMN-4 and FMN-2 signals are observed, and on the screen of the indicator 6.3

a single spectral component is observed (Fig. 2c).

If the FMN-2 signal arrives at the device input, then at the output of the bandwidth

The filter 11.3 produces a frequency-manipulated signal with the frequency deviation index h 1. At the same time, its spectrum is transformed into two spectral components at frequencies 4 fc and 4 fr. And at the output of the bandpass filter 11.3, two spectral components are formed at frequencies of 8 fi and 8 fa (Fig. 2d).

If the FMN-3 signal arrives at the device input, then at the outputs of the bandwidth

filters 11.2 and 11.3 form three spectral components at 4 fi, 4 fCp, 4 fc and 8ft, 8 fc, 8 f2, i.e. the continuous spectrum is transformed into three spectral components (Fig. 2e).

At the output of the multiplier 10.1, the FMN-3 spectrum is transformed into another continuous spectrum, since h 1. Thus, on the screens of indicators b and 6.1, continuous spectra will be observed visually.

If the device receives an FMN-5 signal, then at the output of the multiplier 10.3 its continuous spectrum transforms into five spectral lobes with peak values at frequencies of 8 fi, 8 fs, 8 fcp, 8 fa and 8 fz. At the outputs of multipliers 10.1 and 10.2, the continuous spectrum of the FMNN-5 signal is transformed into continuous spectra, since in these cases h 1, Thus, on the screens of indicators 6, 6.1 and 6.2, continuous spectra will be observed: five spectral petals (Fig. 2e),

If a device receives a linear frequency modulated (chirp) signal

Uc (t) - Uc COS (2 71 fc t + + + pc),,

AfA where y is the frequency change rate.

I with inside pulse;

ATd is the frequency deviation, then after frequency conversion and summation, the output voltage of adder 14 is formed

Uf2 (t) tpr t + Jryt2 +

+ rpr,.

which arrives at the Bragg cell 3 and at the two inputs of the multiplier 10.1, the output of which is a chirp signal

Ue (t) Ue cos (4 l: fnp t +

+ 2 l-ut.2 + 2rpr), which is separated by a band-pass filter 11.1 and is fed to a Bragg cell 3.1. Since the duration of the Tc of the chirp signal at the fundamental and doubled intermediate frequencies is the same, a twofold increase occurs due to a twofold increase in the frequency deviation D Td. It follows from this that the width of the spectrum of the chirp signal at the doubled intermediate frequency is twice as wide as its width at the main intermediate frequency (A f2 2 Afc).

Similarly, at the multiplier outputs, the width of the chirp signal spectrum is increased by 4 and 8 times. Consequently, on the screen of indicator 6, the spectrum of the chirp signal is visually observed, and on the screens of indicators 6.1-6.3, spectra of signals are observed whose width is 2, 4 and 8 times larger than the width of the spectrum of the original chirp signal (Fig. 2g). This is a sign of recognition of the chirp signal.

If a spurious signal (noise) is received in the image channel at a frequency oo, then the following voltages are distinguished by amplifiers 9 and 12 of the intermediate frequency:

Unp4 (t) Unp-jCOS 2 Я fnp t - pnp

Unp5 (t) UnPlCOS 2 7Г fnp t, + 900,, rAeUnpa 1 / 2k2VnVr;

fnp. - f n + fr - intermediate frequency; 5uztsr - (intermediate initial

phase; .

Vn, fn, is the amplitude, frequency, and initial phase of the interference voltage.

The voltages Unp4 (t) and Unpe (t) applied to the two inputs of the adder 14 are compensated at its output. Consequently, the false signal (interference) received by. the image channel at the frequency fa, is suppressed.

5 If a false signal (interferer) is received on the first combination channel at frequency fki (Fig. 5), then the following voltages are allocated to amplifiers 9 and 12. The intermediate frequency: 0 Unp7 (t) Unp., Cos 2jrfnp (t), :

Unpg (t) fnp (t) - php, + 90 °, where fnp 2 fr - fki is the intermediate frequency. The voltage Unps (t) from the output of the intermediate frequency amplifier 12 is fed to the 5th input of the phase shifter 13 by 90 °, the output of which is the voltage Unpe (t) UnPl cos (2 and fnp t - pnp, + 90 ° + 90 °) - UnpjCos (2 and fnp t -), 0 «t sjrc.

0 The voltages Unp7 (t) and Unpg (t) supplied to the two inputs of the adder 14 are compensated at its output. Consequently, a spurious signal (interference) received on the first combination channel at the frequency 5 is suppressed.

If a false signal (interferer) is received via the second combination channel at a frequency of o k2 t °, the following voltages are separated by amplifiers 9 and 12 of the intermediate frequency:

Unp „(t) and the pump (2 l.fnp t + pnPi); UnpH (t) Unp2cos (+ + np, -90 °),,

with where fnp fk2-. 2 fr - intermediate frequency.

Unp ,, (t) voltage from amplifier output

12 intermediate frequency arrives at

- input phase shifter 13 at 90 °, at the exit

whose voltage is 0Unpii. (t) (2 liters fnp t + / Vip,

- 90th + 90 °) ipgso8 (2 fnp t + + pnp),.

The voltages Unp (t) and Unp v, (t) are fed to the two inputs of the adder 14, the output of which is the voltage

ILJt) and Ј03 (2 L fnp t + y) pr (), 0 «t Гс, rfleUSi 2 UnP2.

This voltage is applied to the second input of the multiplier 15, and the received signal (noise) is fed to the first input. On

the output of the multiplier 15 is a voltage

Ue (t) Ue cos (4 l fg t + fk) +

+ U6 cos 2 n (fk.- 2 fr) +

+, O-St-src, rfleV6 1 / 2k2VnVSJ, which does not fall into the passband of the narrowband filter 16. The key 18 does not open and the spurious signal (interference) received over the second combinational channel at the frequency Odo is suppressed.

Thus, the proposed device in comparison with the prototype provides increased noise immunity and selectivity. This is achieved by suppressing spurious signals (interference) received over additional (mirror and combinational) channels.

Claims (1)

Invention Formula An acousto-optical spectrum analyzer containing the first mixer, one input connected to the receiving antenna, the other to the output of the local oscillator, and the output to the input of the first intermediate frequency amplifier, three multipliers, three band-pass filters, and a laser, a collimator and the four Bragg cells, each of which, along the beam diffracted in it, through the corresponding lens, are optically coupled to the corresponding photodetector matrix set in. the focal plane of this lens and the output connected to the corresponding indicator, while the output of the first multiplier through the first band-pass filter connected to the outputs of the second multiplier and the piezoelectric transducer of the second Bragg cell, the output of the second multiplier through the second band pass the filter is connected to the inputs of the third multiplier and the piezoelectric transducer of the third Bragg cell, and the output of the third multiplier through the third band-pass filter to the piezoelectric transducer of the fourth Bragg cell, characterized in that, in order to improve the noise immunity and selectivity, a second mixer and a second intermediate amplifier are introduced into it frequencies, two phase shifters at 90 °, adder, fourth multiplier, narrowband filter, amplitude detector and key, with the first inputs of the second mixer and four the multiplier is connected to the receiving antenna, the second input of the second mixer is connected through the first phase shifter by 90 ° to the second output of the local oscillator, and the output through the second intermediate frequency amplifier and the second phage connected in series Spinner 90 ° - with the second input of the adder, the first input of which is connected to the output of the first intermediate frequency amplifier, and the output - to the second input of the fourth multiplier and the first input the key, the output of which is connected to the inputs of the first multiplier and the piezoelectric transducer of the first Bragg cell, and the second input through the series-connected narrow-band filter and the amplitude detector to the fourth multiplier. / at V VX / well -J7 BUT tfffo-3 fe X2 X4x8 s V y at J Јy m with Fg -L 2G BUT Have / / 5Л V. ft & J FIG. five A # / / "