RU2009512C1 - Oscillographic spectrum analyzer - Google Patents

Abstract

FIELD: radio-measurement technology. SUBSTANCE: analyzer has sweep generator, heterodyne, mixer, intermediate frequency amplifier, detector, delay line, four cathode-ray tubes, switch, frequency-by-eight multipliers, frequency-by-eight dividers, band-pass filters, controlled delay unit, multiplier, narrow band filter, phase detector, control unit, frequency detectors, differentiating units, amplitude detector, saw-tooth voltage generator, rectifier, reference voltage generator, phase shifter for 90 deg, amplifiers, frequency-by-two multiplier, frequency-by-four multiplier, spectrum width meters, comparison units, threshold members, OR gate, amplitude limiter and sync detector. EFFECT: improved precision of measurement. 5 dwg

Description

 The invention relates to radio measurement technology and can be used in radar and communications.

 The purpose of the invention is the expansion of functionality by visually evaluating the main parameters of the signal with combined amplitude modulation, linear frequency modulation and phase shift keying (AM = LFM = PSK).

 In FIG. 1 shows a structural diagram of the proposed analyzer; in FIG. 2 is a block diagram of a detector; in FIG. 3 and 4 are timing diagrams explaining the operation of the analyzer; in FIG. 5 is a view of waveforms.

The oscillographic spectrum analyzer contains a sweep generator 1, a local oscillator 2, a mixer 3, an intermediate frequency amplifier 4, a detector 5, a delay line 6, a cathode ray tube (CRT) 7, a key 8, a frequency multiplier 9 by eight, a frequency divider 10 by eight, band-pass filter 11, adjustable delay unit 12, multiplier 13, band-pass filter 14, frequency multiplier 15 by eight, frequency divider 16, eight, narrow-band filter 17, phase detector 18, control unit 19, frequency detector 20, differentiating unit 21, amplitude detector 22, di fferentsiruyuschy unit 23, a generator 24, a sawtooth voltage, a CRT 25, a frequency detector 26, a rectifier 27, a reference voltage generator 28, a phase shifter 29 to ^90, amplifiers 30 and 3, the CRT 32, a multiplier 33, the frequency by two, a multiplier 34, the frequency by four, a frequency multiplier of 35 by eight.

 The detector comprises spectral width meters 36-39, comparison blocks 40-42, threshold elements 43-45, OR element 46, amplitude limiter 47, and synchronous detector 48. The analyzer also contains a CRT 49.

 The analyzer works as follows.

Viewing Df predetermined frequency band by using the sweep generator 1, which are periodically with period T _n sawtooth tunable oscillator 2. Simultaneously sweep generator 1 generates a horizontal scan CRT 7 which is used as a frequency axis, and its length corresponds to the frequency range swath . Key 8 in the initial state is closed.

- скорость изменения частоты внутри импульса;
Δ f_д - девиация частоты;
φ_к (t) - манипулируемая составляющая фазы, отображающая закон фазовой манипуляции в соответствии с модулирующим кодом М(t) (фиг. 3а), причем φ_к (t) = const при К τ_и < t < (K + 1) и может изменяться скачком на Δφ при t = K τ_и , т. е. на границах между элементарными посылками (К = 1, 2, . . . , N - 1);
τ_и и N - длительность и количество элементарных посылок, из которых составлен сигнал длительностью Т_с (Т_с = N τ_и ); поступает на первый вход смесителя 3, на второй вход которого подается напряжение гетеродина 2 линейно изменяющейся частоты
u_г(t) = U_г cos (ω_г t + πγ_г t² + φ_г),
0≅t≅T_п, где U_г, ω_г и φ_г - амплитуда, начальная частота и начальная фаза напряжения гетеродина соответственно;
γ_г=

- скорость изменения частоты гетеродина.The received signal with a combined AM-LFM-FMN, which can be described by the following expression: u _c (t) = U [1 + m (t)] cos [ω _c t + πγ t ² + φ _к (t) + φ _c ] , 0≅t≅T _c ,
where U _c , ω _c , T _c and φ _c are the amplitude, initial carrier frequency, duration and initial phase of the signal, respectively;
m (t) is the modulating function by amplitude modulation;
γ =

- rate of change of frequency inside the pulse;
Δ f _d - frequency deviation;
φ _к (t) is the manipulated component of the phase that displays the law of phase manipulation in accordance with the modulating code M (t) (Fig. 3a), and φ _к (t) = const for K τ _and <t <(K + 1) and can change abruptly by Δφ at t = K τ _and , i.e., at the boundaries between elementary premises (K = 1, 2,..., N - 1);
τ _and and N is the duration and number of chips that make up the signal with a duration of T _s (T _s = N τ _and ); enters the first input of the mixer 3, the second input of which is the voltage of the local oscillator 2 of a ramp frequency
u _g (t) = U _g cos (ω _g t + πγ _g t ² + φ _g ),
0≅t≅T _p , where U _g , ω _g and φ _g are the amplitude, initial frequency and initial phase of the local oscillator voltage, respectively;
γ _g =

- rate of change of the local oscillator frequency.

At the output of the mixer 3, voltages of combination frequencies are generated. Amplifier 4 provides an intermediate frequency voltage
u _pr1 (t) = U _pr [1 + m (t)] cos [ω _pr t + πγ t ² +
_To + φ (t) - πγ _r t + φ ² _etc.], where U _ave = 1/2 · K _{1 c} U U _z;
To ₁ - gear ratio of the mixer;
ω _CR = ω _c -ω _g - intermediate frequency,
φ _CR = φ _c -φ _g is the intermediate initial phase, which is fed to the input of the detector 5.

If the input of the analyzer receives a signal with combined amplitude modulation: linear frequency modulation and single phase shift keying (AM-LFM-OFMn), then the following oscillations are generated at the output of frequency multipliers 33-35, respectively:
u ₁ (t) = U _pr [1 + m (t)] cos (ω 2 t + _pr πγ t 2 ² -
- 2 _g πγ t ² + φ 2 _pr)
u ₂ (t) = U _pr [1 + m (t)] cos (4ω _pr t + 4 πγ t ² -
- 4 πγ _r t ² + φ 4 _etc.)
u ₃ (t) = U _pr [1 + m (t) - cos (8 ω _pr t + 8 πγ t ² -
- 8 _g πγ t φ ² + 8 _etc.)
0 ≅ t ≅ T _c .

Since 2 φ _к (t) = 0.2 π, 4 φ _к (t) = 0.4 π, 8 φ _к (t) = 0.8 π, then phase oscillations are already absent in the indicated oscillations.

The width of the spectrum of the second Δ f ₂ , the fourth Δ f ₄ and the eighth Δ f ₈ harmonics is determined by the signal duration T _s (Δ f ₂ = Δ f ₄ = Δ f ₈ = 1 / T _c ).

Since 2 φ _к (t) = 0.2 π, 4 φ _к (t) = 0.4 π, 8 φ _к (t) = 0.8 π, phase manipulations are already absent in the indicated oscillations.

), т. е. ширина спектра указанных гармоник стала в N раз меньше ширины спектра входного сигнала:

=

=

= N .The width of the spectrum of the second Δ f ₂ , the fourth Δ f ₄ and the eighth Δ f ₈ harmonics is determined by the signal duration T _s (Δ f ₂ = Δ f ₄ = Δ f ₈ = 1 / T _c ), while the width Δ f _c AM-LFM -OFMn, the signal is determined by the duration of τ _and its elementary premises (Δf _c =

), i.e., the spectral width of these harmonics has become N times smaller than the spectral width of the input signal:

=

=

= N.

 Therefore, when the frequency of the AM-LFM-OFM n signal is multiplied by two, four, and eight its spectrum is “collapsed” N times.

 This allows you to detect AM-LFM-OFMn signal even when its power at the output of the analyzer is less than the noise power.

The width of the spectrum Δ f _{2 of the} input signal is measured using a meter 36, the width of the spectrum of the second Δ f ₂ , the fourth Δ f ₄ and the eighth Δ f ₈ harmonics of the signal is measured using meters 37-39.

Voltages U ₁ , U ₂ and U ₃ proportional to Δ f ₂ , Δ f ₄ and Δ f _8, respectively, from the output of the measuring instruments 37-39 of the spectral width are fed to the first inputs of comparison blocks 40-42, the second inputs of which are supplied with voltage U s the output of the meter 36 of the spectrum width, proportional to Δ f _c . Since U >> U ₁ , U >> U ₂ , U >> U ₃ , positive pulses are generated at the outputs of comparison blocks 40-42 that exceed the threshold level U of the _pores in the threshold elements 43-45 and through the OR element 46 to the exit.

If the input of the analyzer receives a signal with combined amplitude modulation, linear frequency modulation and double phase shift keying (AM-LFM-DPSK) φ _к (t) = 0, π / 2, π, 3/2 π, then the output of the multiplier 33 the AM-LFM-OFMn signal [φ _к (t) = 0, π, 2 π, 3 π] is formed by two, and the oscillations u ₂ (t) and u ₃ at the output of the multipliers 34 and 35 by four and eight frequencies (t) respectively, i.e., in these channels, the spectrum of the input signal is convolved.

If the input of the analyzer receives a signal with combined amplitude modulation, linear frequency modulation and triple phase shift keying (AM-LFM-TFMn) φ _к (t) = 0, π / 4, π / 2, 3/4 π π, 5/4 π, 3/2 π, 7/4 π, then the convolution of the spectrum is carried out only at the output of the multiplier 35, the frequency of eight. In this case, a positive voltage is generated only at the output of the comparison unit 42.

The voltage from the output of the detector 5 is supplied to the control input of the sweep generator 1, stopping the tuning of the local oscillator 2, to the input of the delay line 6, to the control input of the switch 8, opening it, and to the vertical electrode of the CRT 7. From now on, viewing the specified frequency range Df and the search for AM-LFM-FMN signals stops for the time of visual analysis of the main parameters of the detected AM-LFM-FMn signal, which is determined by the delay time τ _{s of} the delay line 6. In this case, a pulse (frequency mark) is formed on the CRT screen 7, the position of which on the horizontal scan uniquely determines the initial carrier frequency of the received AM-LFM-FMn signal (Fig. 5a).

The threshold level U _then in the detector 5 is selected so that this level does not exceed random interference.

When the tuning of the frequency ω _{g of the} local oscillator 2 ceases, the voltage is released by the intermediate-frequency amplifier 4
u _pr2 (t) = U _pr [1 + m (t)] cos [ω _pr t + πγ t ² +
+ φ _k (t) + φ _pr ], 0 ≅ t ≅ T _c . which through the public key 8 enters the input of the amplitude limiter 47, at the output of which a voltage is generated
u _pr3 (t) = U _ogr cos [ω _pr t + πγ t ² +
+ φ _k (t) + φ _pr ], 0 ≅ t ≅T _c .

where U _ogre is the limiting threshold, which is a signal with combined linear frequency modulation and phase shift keying (LFM-PSK).

 This voltage is supplied to the inputs of a frequency multiplier 9 by eight, a multiplier 13, a frequency detector 20, an amplitude detector 22, and a synchronous detector 48. A voltage is generated at the output of the frequency multiplier 9 by eight (Fig. 3d).

u _pr4 (t) = U _ogr cos [8 ω _pr t + 8 πγ t ² + 8 φ _pr )
0 ≅ t ≅ T _c. . Since 8 φ _к (t) = 0.8 π - with a single phase manipulation, 8 φ _k (t) = 0.4 π, 8 π, 12 π - with a double phase manipulation, 8 φ _k (t) = 0 , 2 π, 4 π, 6 π, 8 π, 10 π, 12 π, 14 π - with three-phase phase-shift keying, the phase shift is already absent in the indicated voltage.

The voltage u _CR4 (t) is supplied to the input of the frequency divider 10 by eight, at the output of which a voltage is generated (Fig. 3d).

_np5 u (t) = U _Res cos [ω _ave t + πγ t + φ ² _etc.],
0 ≅ t ≅ T _c, which is a chirp signal whose frequency varies linearly (Fig. 3c). The voltage u _pr5 (t) is allocated by the band-pass filter 11 and is supplied to the input of the adjustable delay unit 12. A voltage is generated at the output of the indicated block.
_pr6 u (t) = U _Res cos [ω _ave (t-τ) + πγ ( t-τ) + φ ² _etc.],
0 ≅ t ≅ T _c, which is fed to the second input of the multiplier 13, to the first input of which the LFM-PSK intermediate frequency signal u _pr3 (t) is supplied. At the output of the multiplier 13, a beat voltage is generated (Fig. 4b)
u _b1 (t) = U _b cos [ω _b t + φ _k (t) + φ _b ],
0 ≅ t ≅ T _c, where U _b = 1/2 · K ₂ U ² _ogre ,
K ₂ is the transmission coefficient of the multiplier;
ω _b = 2πγτ is the beat frequency;
φ _b = ω _pr τ-πγτ ² is the initial phase of the beats, which is the PSK signal at the beat frequency, and the beat frequency ω _b is determined by the rate of change of the signal frequency γ and the delay value τ.

The voltage u _b1 (t) is allocated by the band-pass filter 14 and is fed to the input of the multiplier by eight, the output of which produces a harmonic voltage (Fig. 4B).

u _b2 (t) = U _b cos (8 ω _b t + 8 φ _b ), 0 ≅ t ≅ T _c .

The voltage u _b2 (t) is supplied to the input of an eight frequency divider 16, the output of which is voltage (Fig. 4d)
u _b3 (t) = U _b cos (ω _b t + φ _b ), 0 ≅ t ≅ T _c . , which is a harmonic oscillation at a frequency of ω _b . The voltage u _b3 (t) is allocated by a narrow-band filter 17 and is supplied to the first input of the phase detector 18, the second input of which is supplied with voltage from the output of the reference voltage generator 28
u _o (t) = U _o cos (ω _o t + φ _o ), where U _o , ω _o and φ _o are the amplitude, frequency and initial phase of the generator voltage, respectively.

If these voltages differ in frequency or phase, then a constant voltage is generated at the output of the phase detector 18, the amplitude and polarity of this voltage depending on the degree and voltage of the deviation of the beat frequency ω _b from the frequency of the reference voltage generator 28. The control voltage with the help of the control unit 19 acts on the adjustable delay unit 12, changing the delay value τ so that the equality
ω _b = 2πγτ = ω _o
To visually assess the magnitude of the phase jumps Δφ and the multiplicity of phase manipulation n of the received AM-LFM-FMN signal, a circular CRT 25 is used, and a circular scan is generated using the reference voltage generator 28, the frequency ω _{o of} which is maintained equal to the beat frequency ω _b (ω _o = ω _b ) using the system of automatic frequency control. The voltage u _o (t) of the generator 28 is supplied through the amplifier 31 to the vertical electrode, and through the phase shifter 29 to the amplifier 30 to the horizontal electrode of the CRT 32.

The voltage u _b1 (t) (Fig. 4b) from the output of the band-pass filter 14 simultaneously enters the input of the frequency detector 26, the output of which forms short bipolar pulses (Fig. 4e), the temporary position of which corresponds to the moments of the abrupt change in the phase of the signal u _b1 (t ) (Fig. 4b). At the output of the rectifier 27, a sequence of short positive pulses is formed (Fig. 4f), which is fed to the modulating electrode of the CRT 32 and modulates its electron beam of brightness. On the screen of the CRT 32, an image is formed in the form of several bright points located on a circle (Fig. 5c, d, e). The number of points determines the multiplicity of phase manipulation, and the angular distance between them is equal to the phase jump Δφ of the detected AM-LFM-QPSK signal. With the frequency inequality ω _b and ω _o (ω _b ≠ ω _o ), the brightness marks move around the circle with a difference frequency.

 To obtain a stable waveform on the CRT 32 screen, the PLL system is used, the operation of which is described.

To visually assess the law of phase manipulation, the duration and number of N chips, as well as the parameters of linear frequency modulation, the voltage (Fig. 3b) from the output of the amplitude limiter 47 is simultaneously supplied to the inputs of the frequency 20 and amplitude 22 detectors. At the output of the frequency detector 20, a voltage is generated (Fig. 3e), proportional to the law of variation of the frequency of the received signal (Fig. 3c), with short bipolar pulses at the moments of an abrupt change in the phase of the signal (Fig. 3b). This voltage by the differentiating unit 21 is converted into a rectangular voltage (Fig. 3g), which is supplied to the vertical electrode of the CRT 25. The amplitude detector 22 detects the envelope of the signal (Fig. 3h), which by the differentiating unit 23 is converted into two short unipolar pulses (Fig. 3i) moreover, a positive short pulse starts, and a short negative pulse turns off the sawtooth voltage generator 24, the output voltage of which (Fig. 3k) is used to form a horizontal scan of CRT 25. When this, a voltage in the form of a rectangular pulse with short and bipolar pulses is formed on the CRT screen 25 at its apex (Fig. 3g) and (Fig. 5b), and the duration T _{from the} detected AM-LFM-FMN signal, the pulse amplitude is proportional to the rate of change of frequency γ inside the signal, and the pulse area is proportional to the frequency deviation Δ f _d (Δ f _d = γ T _s ) of the received AM-LFM-FMN signal.

.The number of short bipolar pulses is equal to the number of phase m jumps of the received AM-LFM-FMN signal. Between the number of phase jumps m and the number of chips N there is the following analytical dependence
N = 0.5 (m + 1). By counting the number of jumps of phase m, one can determine the number N of elementary premises. Estimating T _c and N, we can determine the duration of τ _and elementary premises τ _u =

.

The voltage u _pr1 (t) from the output of the intermediate frequency amplifier 4 through the public key 8 is simultaneously supplied to the second input of the synchronous detector 48, at the output of which a low-frequency voltage is generated
u _n (t) = U _n [1 + m (t)], 0 ≅ t ≅ T _c , where U _n = 1/2 · K ₃ U _pr U _ogre ;
To ₃ - the transfer coefficient of the synchronous detector 48.

 This voltage is supplied to the vertical electrode of the CRT 49, the horizontal electrode of which is connected to the output of the sawtooth voltage generator 24. On the screen of a CRT 49 a low-frequency voltage is generated (Fig. 5e), by visual analysis of which it is possible to determine the law of amplitude modulation m (t).

The delay time τ _{s of} the delay line 6 is selected so that it is possible to visually evaluate the main parameters of the detected AM-LFM-FMN signal by observing the oscillograms on the CRT screens 7, 25, 32 and 49. After this time, the voltage from the output of the delay line 6 is supplied to the inputs reset threshold elements 43-45 and resets their contents to zero. In this case, the sweep generator 1 is transferred to the tuning mode, and the key 8 is closed, i.e., it is transferred to its original state. From this point in time, viewing the specified frequency range D and searching for AM-LFM-PSK signals continues. In case of detection of the next AM-LFM-PSK signal, the analyzer operates in a similar manner. (56) Copyright certificate of the USSR N 1626241, cl. G 01 R 25/00, 1988.

Claims (1)

SPECTRA OSCILLOGRAPHIC ANALYZER ANALYSIS, comprising a series-connected sweep generator, local oscillator, mixer, intermediate-frequency amplifier, a detector, the second input of which is connected to the output of the delay line, and the output is connected to the inputs of the scan line delay generator and to the second input of the key, the first input of which is connected to the output an intermediate frequency amplifier, and the key output is connected to the vertical electrode of the first cathode ray tube, the horizontal electrode of which is connected to the second output of the generator scanning a series connection of a generator of reference voltage, phase shifter 90 ^o, a first amplifier and a horizontal electrode of the second cathode-ray tube, the vertical electrode which through a second amplifier connected to the output reference voltage generator, and a modulating electrode connected to the output of the rectifier in series-connected first frequency multiplier by eight, the first frequency divider by eight, the first band-pass filter, an adjustable delay unit, the first multiplier, the second band-pass filter and the second hour a total detector, a first amplitude detector, a differentiating unit and a sawtooth voltage generator connected in series with an output connected to the horizontal electrodes of the third cathode ray tube, the second input of the mixer connected to the input of the device, the second input of the multiplier connected to the inputs of the amplitude detector and the second frequency detector, the output of which through the second differentiating unit is connected to the vertical electrode of the third cathode ray tube, the output of the first band-pass filter h A second frequency multiplier is eight, a second frequency divider is eight, a narrow-band filter, a phase detector and a control unit are connected to the second input of the adjustable delay unit, the second input of the phase detector is connected to the output of the reference voltage generator, and the input of the multiplier is connected to the input of the first frequency multiplier by eight, characterized in that, in order to expand the functionality by visually assessing the main parameters of the signal with combined amplitude modulation, linear frequency modulation phase shift keying, an amplitude limiter, a synchronous detector, and a fourth cathode ray tube are introduced into it, the input of the amplitude limiter connected to the key output, and the output to the input of the first frequency multiplier by eight, to the first input of the synchronous detector, the second input of which is connected with the key input, and the output is connected to the vertical electrode of the fourth cathode ray tube, the horizontal electrode of which is connected to the output of the sawtooth voltage generator.

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