RU2344430C1 - Device for frequency measurement of input system of panoramic radio receiver - Google Patents

Abstract

FIELD: physics, radio.

SUBSTANCE: device presented relates radio measuring equipment and can be used for passive radio control during the solving of problems of hidden characterisation of impulse signals with increased interference immunity and secrecy. Device for frequency measurement of input signals of a panoramic radio receiver contains a reception antenna, input circuit, high frequency amplifier, first and second asynchronous detectors, heterodyne, first and second video frequency amplifier, differentiating circuit, first and second observation oscilloscope, which have vertical-deflecting and horizontal-deflecting plates, forming unit of frequency analysing, 90° phase changer, pulse former and first - third keys, control unit, switch, frequency width gauge, time-interval counter, time-and-frequency matrix former, comparing unit and memory block and analysis, accordingly connected in between themselves.

EFFECT: increase in the functionality of the device.

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Description

The proposed device relates to a radio engineering technique and can be used for passive radio monitoring in solving the problems of covertly determining the characteristics of pulse signals with increased noise immunity and stealth (short-term burst signals, signals with frequency-hopping and other pulse signals).

Known devices for measuring the frequency of the input signal of a panoramic radio receiver (ed. Certificate of the USSR No. 1.000.930, 1.272.266, 1.354.124, 1.406.506, 1.531.018, 1.557.532, 1.661.661, 1.742.741, 1.832 .215; RF patents ı2.010.245, 2.025.737, 2.030.750, 2.279.097 and others).

Of the known devices, the closest to the proposed one is “A device for measuring the frequency of the input signal of a panoramic radio receiver” (RF patent No. 2.279.097, G01R 23/10, 2004), which is selected as a prototype.

It should be noted that to represent any signal, it is enough to know its carrier frequency and the two-component vector process - the complex envelope. Although the carrier frequency may be large, the complex envelope remains a relatively low frequency signal that can be digitized.

Any signal in the most general form can be represented as follows:

- комплексная огибающая сигнала;Where

- complex envelope of the signal;

U (t) is the envelope (amplitude varying in time) of the signal;

φ (t) = φ _n (t) + φ _o - phase of the signal;

φ _n (t) is the nonlinear component of the phase;

φ ₀ is the initial phase;

ω _c t is the linear component;

ω _с - carrier circular frequency (ω _с = 2πf _c ).

Given the Euler formulas, the complex envelope of the signal is written as follows:

In this case, the signal u _c (t) is expressed as the real part of the complex signal

We consider the complex envelope of the signal at certain values of the phase φ (t).

If the phase of the signal φ (t), changing at some points in time, takes the values either 0 or π, then

where the plus sign corresponds to the phase value φ ₁ = 0, and the minus sign corresponds to the phase value φ ₂ = π.

Thus, in this case, the complex envelope of the signal is a real function of time, and the original signal can be written as

whence it follows that the signal has amplitude modulation (AM) and phase shift keying (QPSK). In this case, the amplitude modulation is determined by the envelope of the signal U (t), and the phase shift is determined by the factor cosφ (t), which takes the value ± 1.

If the phase of the signal φ (t) takes the value ± π / 2, then the complex envelope of the signal is an imaginary function of time

The signal in this case is described by the expression

and also has amplitude modulation and phase shift keying determined by the factor sinφ (t) = ± 1.

In the general case, the complex envelope of a signal can be represented as the sum of two components, i.e.

where the index "c" means the real (real) part, and the index "m" is imaginary.

It follows from the last expression that

содержит действительную U_в(t) и мнимую U_м(t) составляющие, то фаза сигнала φ(t) является произвольной функцией времени и, следовательно, сигнал u_c(t) обладает частотной (угловой) модуляцией.So if the complex envelope

contains the real U _in (t) and imaginary U _m (t) components, then the phase of the signal φ (t) is an arbitrary function of time and, therefore, the signal u _c (t) has frequency (angular) modulation.

The known device allows to increase the accuracy of measuring the carrier frequency of pulsed signals and eliminates the inherent ambiguity of superheterodyne receivers in determining the frequency due to reception through additional (mirror, Raman and intermodulation) channels, and also provides the opportunity for visual analysis of the complex envelope of pulsed signals.

It should be noted that to ensure reliable communication in the conditions of organized and unintentional interference, multipath propagation of radio waves, as well as multiple access when working in packet radio networks, the best results can be obtained using signals with pseudo-random tuning of the operating frequency (MFC).

Among the signals with frequency manipulation, these signals have high noise immunity, energy, structural, information, temporal and spatial stealth and are widely used in single-channel radio communication systems with frequency hopping (Fig. 5).

An object of the invention is to expand the functionality of the device by determining, recording and analyzing the grid of used signal frequencies with pseudo-random tuning of the operating frequencies.

The problem is solved in that the device for measuring the frequency of the input signal of the panoramic radio receiver, containing in accordance with the closest analogue a series-connected receiving antenna, an input circuit, a high-frequency amplifier, a first asynchronous detector, the second input of which is connected to the local oscillator output, the first video amplifier, a differentiating circuit and vertically deflecting plates of the first oscilloscope indicator, horizontally deflecting plates of which are connected to the output of the cha forming unit a frequency sweep, a 90 ° phase shifter connected to the local oscillator output, a second asynchronous detector, the second input of which is connected to the high-frequency amplifier output, a second video amplifier and horizontally-deflecting plates of the second oscillographic indicator, a pulse shaper and a first switch connected in series to the output of the differentiating circuit, the second input of which is connected to the output of the first video amplifier, and the output is connected to the vertically-deflecting plates of the second oscillographic indicator at the same time, the control inputs of the input circuit, high-frequency amplifier, local oscillator and the frequency sweep generation unit are connected to the corresponding outputs of the control unit, differs from the closest analogue in that it is equipped with a switch, second and third keys, a bandwidth meter, a time interval meter , a shaper of the time-frequency matrix, a comparison unit, and a memory and analysis unit, and a switch, a second key, and a second are connected in series to the output of the first asynchronous detector the input of which is connected to the output of the pulse shaper, a bandwidth meter, a frequency-time matrix shaper, the second input of which is connected to the output of the second key through a time interval meter, a comparison unit, the second input of which is connected to the output of the memory and analysis unit, and a third key the second input of which is connected to the output of the shaper of the time-frequency matrix, and the output is connected to the input of the memory and analysis block.

The structural diagram of the proposed device is presented in figure 1. A view of the possible waveforms is shown in FIGS. 2 and 3. Timing diagrams explaining the principle of operation of the device are shown in FIG. 4. A fragment of the time-frequency matrix of a signal of a single-channel radio communication system with pseudo-random tuning of the operating frequency is shown in Fig. 5.

A device for measuring the frequency of the input signal of a panoramic radio receiver includes a receiving antenna 1 connected in series, an input circuit 2, a high-frequency amplifier 4, a first asynchronous detector 6, the second input of which is the output of the local oscillator 5, the first video amplifier 8, the differentiating circuit 9, and the vertically-deflecting plates of the first oscillographic indicator 10, the horizontal deflecting plates of which are connected to the output of the frequency sweep generating unit 7, connected in series to the output of the 5 phase oscillator a splitter 11 by 90 °, a second asynchronous detector 12, the second input of which is connected to the output of the high-frequency amplifier 4, the second video amplifier 13 and the horizontally-deflecting plates of the second oscilloscope indicator 16 connected in series to the output of the differentiating circuit 9 of the pulse phase shifter 14, the first key 15, the second input of which is connected to the output of the first video amplifier 8, and the vertically-deflecting plates of the second oscilloscope indicator 16, connected in series to the output of the first asynchronous detector 6 in the switch 17, the second key 18, the second input of which is connected to the output of the pulse shaper 14, the bandwidth meter 19, the frequency-time matrix shaper 21, the second input of which is connected to the output of the second key 18 through the time interval meter 20, the comparison unit 22, the second the input of which is connected to the output of the memory and analysis unit 24, and a third key 23, the second input of which is connected to the output of the frequency-time matrix driver 21, and the output is connected to the input of the memory and analysis unit 24. In this case, the control inputs of the input circuit 2, the high-frequency amplifier 4, the local oscillator 5 and the frequency sweep generating unit 7 are connected to the corresponding outputs of the control unit 3.

The principle of operation of the proposed device is based on the use of an asynchronous method for receiving and measuring the carrier frequency of pulse signals during a quick search in frequency. In this case, asynchronous detectors 6 and 12 ensure the transfer of the carrier frequency envelope to zero with decomposition into the real (in-phase) and imaginary (quadrature) components, respectively.

For the visual display of the complex envelope, several different formats are provided.

In-phase and quadrature components at the outputs of asynchronous detectors 6 and 12, representing respectively the real U _in (t) and imaginary U _m (t) parts of the complex envelope of the input signal, can be visually displayed as waveforms in Cartesian coordinates. If the oscillogram is synchronized by the clock frequency of the received signal with discrete manipulation, then the visual display takes the form of the so-called “eye diagram”.

More informative for signals with digital modulation is the vector format representation of the complex envelope in polar coordinates on the complex plane. The vector module reflects the instantaneous amplitude (envelope) of the signal, and the angle represents the current phase value. An analysis of the trajectories of the complex vector in measuring time allows one to recognize the type of modulation and evaluate its parameters.

The device operates as follows.

The search for pulsed signals in a given frequency range Df is carried out using the control unit 3, which periodically with a period T _p linearly changes the frequency of the local oscillator 5 (figure 4, a)

u _g (t) = U _g cos (ω _g t + πγt ² + φ _g ), 0≤t≤T _p ,

where U _g , ω _g , φ _g , T _p - amplitude, initial frequency, initial phase and the repetition period of the local oscillator frequency;

- скорость изменения частоты гетеродина (скорость перестройки).

- rate of change of the local oscillator frequency (tuning rate).

The received pulse signal, for example, at a frequency of ω ₁ (figure 4, a)

u ₁ (t) = U ₁ cos (ω ₁ t + φ ₁ ), 0≤t≤τ ₁ ,

where U ₁ , ω ₁ , φ ₁ , τ ₁ - amplitude, carrier frequency, initial phase and signal duration,

after passing the receiving antenna 1, the input circuit 2, and the high-frequency amplifier 4, it simultaneously enters the first inputs of the asynchronous detectors 6 and 12, the second inputs of which supply the voltage u _g (t) of the local oscillator 5 directly and through the phase shifter 11 by 90 °, respectively.

The nature of the change in the frequency of the local oscillator 5 is set by the control unit 3, which simultaneously performs the rearrangement of the input circuit 2, the high-frequency amplifier 4, the local oscillator 5 and the frequency sweep generating unit 7, while the condition U _g >> U ₁ is observed. Asynchronous detectors 6 and 12 transfer the envelope of the carrier frequency to zero with the location on the real U _in (t) and imaginary U _m (t) components, respectively.

At the outputs of asynchronous detectors, frequency-modulated oscillations with a difference frequency Ω (t) are generated (Fig. 4, b)

which are highlighted by video amplifiers 8 and 13, respectively.

When calculating the time from the moment when Ω (t) passes through the zero value (ω _and t + πγt ² -ω ₁ ), the oscillations at the output of the asynchronous detectors 6 and 12 can be represented by the expressions:

U _in (t) = U _m (t) cos (φ _o -πγt ² ),

U _m (t) = U _m (t) sin (φ _o -πγt ² ), 0≤t≤τ ₁ ,

where φ ₀ is the random initial phase of the difference oscillation at time t = 0;

U _m (t) is the envelope of the pulse signal at the output of asynchronous detectors 6 and 12.

Denoting the moment of zero beats by t ₀₁ , the oscillation at the outputs of the asynchronous detectors 6 and 12 can be represented as follows:

U _in (t) = U _m (t) cos [φ ₀ -π (tt ₀₁ ) ² ],

U _m (t) = U _m (t) sin [φ ₀ -π (tt ₀₁ ) ² ], 0≤t≤τ ₁ .

The indicated vibrations at | πγ (tt ₀₁ ) ² | >> 1 have a shape that is close to sinusoidal within one cycle, and at | πγ (tt ₀₁ ) ² | <1 the waveform is strongly distorted, and the nature of the distortion is determined by the initial phase φ ₀ .

The minimum value of Ω (t) is

The duration of this oscillation region is approximately equal

The oscillation of U _in (t) from the output of the video amplifier goes to the input of the differentiating circuit 9, at the output of which a voltage is generated (figure 4, c)

, 0≤t≤τ₁.

, 0≤t≤τ ₁ .

This shows that at the moment of zero beats after the differentiating circuit 9, the voltage is zero.

Denote φ (t) = φ ₀ -πγ (tt ₀ ) ² , then

Using this feature, it is possible to determine more precisely the instantaneous frequency of the frequency-modulated signal. The report of the indicated frequency is carried out by visual observation on the screen of the oscilloscope indicator 10 with a linear scan of the voltage U '(t) (figure 2) and calibrated time stamps. In this case, the error in measuring the frequency is (0.5-1%) of the entire working range Df.

At the moment of zero beats, the shaper 14 generates a pulse (Fig. 4, d), which arrives at the control input of the key 15 and opens it. In the initial state, the key 15 is always closed. In this case, the low-frequency voltages from the outputs of the video amplifiers 8 and 13 are supplied to the vertically-deflecting and horizontally-deflecting plates of the oscilloscope indicator 16, forming an image on its screen, the features of which are used by visual observation to determine the type of modulation of the received signal.

It should be noted that the task of determining the type of modulation of the received signal is considered as the task of determining the nature of the functions U _m (t) and φ (t), which, depending on the encoding method of the transmitted information, can be either continuous or discrete.

A possible type of waveform for signals with different types of modulation (manipulation) is shown in Fig.3.

The operation of the device described above corresponds to the case of receiving a pulse signal at a frequency of ω ₁ (Fig. 4, a).

If the pulse signal is received at a frequency of ω ₂ , for example, then the operation of the device occurs in a similar way.

If the signal from the frequency hopper is fed to the input of the device, then a lot of bright points are formed on the screen of the oscilloscope indicator 16 (Fig. 3, FSK), observing which the operator closes the switch 17.

At the moment of zero beats, the shaper 14 generates a pulse (Fig. 4, d), which arrives at the control input of the key 18 and opens it. In the initial state, the keys 18 and 23 are always closed.

In this case, the received signal from the frequency hopper from the output of the first asynchronous detector 6 through the closed switch 17 and the public key 18 is fed to the inputs of the meters of the frequency band 19 and time intervals 20, where the width Δf _c of the frequency band of each frequency channel and the time t _{c of} operation on one frequency respectively. The measured values are fed to the inputs of the formation of the 21 time-frequency matrix (figure 5).

The time interval between frequency switching is called the duration of the frequency element and characterizes the operating time at one frequency t _c .

To compare different radio communication systems with frequency hopping, one of the distinguishing features is the frequency jump rate per unit time. On this basis, radio communication systems are distinguished with a slow, medium and fast speed of tuning of frequency elements.

Since this speed is not standardized, conventionally, tuning is considered slow at 100 ... 300 jumps per second (cps), and at 1000 cps and more, fast tuning takes place; the frequency hopping between these two values is considered average. Although the frequency hopping frequency is used when comparing radio communication systems, however, it is of indirect importance.

The most important parameter of any radio frequency communication system with frequency hopping in terms of noise immunity is the actual operating time at one frequency t _c . This parameter characterizes the ability of radio communication systems with frequency hopping to "move away" from organized interference.

Figure 5 shows a fragment of the time-frequency matrix of the signal of a single-channel RF communication system with frequency hopping, where squares with oblique hatching indicate the frequency channels occupied by the signal elements. In such a radio communication system, in the interval between frequency switching, there is only one carrier frequency and a corresponding transmission channel.

The measured values of the width Δf _{c of the} strip of each frequency channel and the time t _{c of} operation in digital form are transmitted to the shaper 21 of the time-frequency matrix, where the time-frequency matrix is digitally generated (Fig. 5). The latter enters the first input of the comparison unit 22, the second input of which is supplied with the codes of the previously measured values Δf _c and t _c from the memory unit 24. In the initial state, in the block 24 of the memory information is missing.

If the compared codes of the indicated time-frequency matrices are not equal, then the comparison unit 22 generates a constant voltage, which is supplied to the control input of the key 23, opening it. In this case, the code of the generated time-frequency matrix via the public key 23 enters the memory and analysis unit 24, where it is recorded in its memory.

When the signal is repeatedly received from the frequency hopping system of the same radio communication system, the compared time-frequency matrix codes will be equal and there is no voltage at the output of the comparison unit 22, the key 23 is closed.

Therefore, the re-registration of the signal parameters with the frequency hopping of the same radio communication system does not occur.

The device allows to increase the accuracy of measuring the carrier frequency of pulsed signals, to eliminate the ambiguity in determining the frequency inherent in superheterodyne panoramic radio receivers by eliminating reception through additional (mirror, Raman and intermodulation) channels and visually determine the type of modulation (manipulation) of the received pulse signal. This is achieved by the fact that the spectrum of the received high-frequency pulse signal is transferred to the region of zero frequency with the expansion of the envelope into real and imaginary components, respectively. Therefore, the reception of false signals (interference) through mirror, Raman and intermodulation channels is excluded.

In addition, the device acts as a vector analyzer and, unlike meters that operate with scalar (one-dimensional) processes, processes complex envelopes representing the amplitude and phase of the received pulse signal. This allows you to study the amplitude and phase spectra, as well as simultaneously select the amplitude, phase and frequency of the received pulse signal and display them in the form of spectral, time or vector diagrams.

Thus, the proposed device in comparison with the prototype allows you to determine, record and analyze the grid of the used frequencies of the received signal with pseudo-random tuning of the operating frequencies. These signals have high noise immunity, structural, energy, information, temporal, spatial secrecy and are widely used in radio communication systems with frequency hopping. Thus, the functionality of the device is expanded.

Claims (1)

A device for measuring the frequency of the input signal of a panoramic radio receiver, comprising a receiving antenna, an input circuit, a high-frequency amplifier, a first asynchronous detector, the second input of which is connected to the local oscillator output, a first video amplifier, a differentiating circuit and vertically-deflecting plates of the first oscillographic indicator, horizontally the deflecting plates of which are connected to the output of the frequency sweep forming unit, connected in series to the output of the phase local oscillator 90 ° switcher, a second asynchronous detector, the second input of which is connected to the output of the high-frequency amplifier, a second video amplifier and horizontally-deflecting plates of the second oscilloscope indicator, a pulse shaper and a first key, the second input of which is connected to the output of the first video amplifier, in series and the output is connected to the vertically-deflecting plates of the second oscilloscope indicator, while the control inputs of the input circuit, high-frequency amplifier , the local oscillator and the frequency sweep generation unit are connected to the corresponding outputs of the control unit, characterized in that it is equipped with a switch, second and third keys, a bandwidth meter, a time interval meter, a time-frequency matrix shaper, a comparison unit and a memory and analysis unit, moreover, to the output of the first asynchronous detector, a switch, a second key, the second input of which is connected to the output of the pulse shaper, a bandwidth meter, f a frequency-time matrix shaper, the second input of which is connected to the output of the second key through a time interval meter, a comparison unit, the second input of which is connected to the output of the memory and analysis block, and a third key, whose second input is connected to the output of the time-frequency matrix shaper, and the output is connected to the input of the memory and analysis unit.

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