SU1548851A1 - Device for suppression of interface with angular modulation - Google Patents

Abstract

The invention relates to radio engineering. The purpose of the invention is to increase the ratio of the power of the useful signal to the power of interference with angular modulation, as well as reduce the distortion of the useful signal in the absence of interference with angular modulation. The device contains band stops 1 and 6, narrowband amplifier 2, amplitude detectors 3 and 7, compensation block 4, balanced modulator 5, key 8, threshold element 9 and correlator 10. The interference suppression device operates in two modes: when the signal and interference, and also when only the useful signal is active. In the first mode, the parasitic modulation of the interference is eliminated with the help of the introduced limiter 1, as a result of which the voltage of the reconstructed useful signal and interference residues is generated at the output of the device. In the second mode, in the absence of powerful broadband frequency-modulated interference, the useful signal passes through the device without distortion, which is ensured by the introduction of the key 8, the threshold element 9 and the correlator 10. 1 Cp. f-ly, 2 ill.

Description

1

The invention relates to radio engineering and can be used in radio receivers when receiving signals under the influence of wideband interference with angular modulation.

The purpose of the invention is to increase the ratio of the power of the useful signal to the power of interference with angular modulation, reduce the distortion of the useful signal in the absence of interference with angular modulation.

Fig. 1 shows the structural electrical circuit of the interference suppression device with angular modulation in Fig. 2, voltage plots explaining the operation of the device.

The angular modulation interference suppression device includes a second bandpass limiter 1, a narrowband amplifier 2, a first amplitude detector 3, a compensation unit 4, a balanced modulator 5, a first band limiter 6c a second amplitude detector 7, a key 8, a threshold element 9, a correlator 10 a broadband amplifier 11.

The device works as follows.

Consider the operation of the interference suppression device in two modes. In the first mode, when the signal and interference is acting (left family of diagrams a, b, c, d, d on), the envelope of the output of the wideband amplifier 11 (Fig. 2a) is constant and equal to the amplitude of the interference A0 "on the time intervals where the signal missing. At time intervals where the signal and interference overlap, beats appear (signal fluctuations) of amplitude, which is indicated by the hatching on the plot of Fig. 02a and other plots. In the main channel, the desired signal passes through the band-pass amplifier 2 without distortion, and the wideband interference acquires parasitic amplitude modulation (frequency-amplitude conversion). Moreover, the spectral width of the parasitic amplitude modulation is a significant fraction or even equal to the spectrum width of the useful signal. After linear amplitude detection in the detector 3, the voltage (Fig. 26) is fed to the first input of the compensation unit 4. This voltage contains a constant component equal to the average value

interference amplitudes, and a variable made up of signal and spurious fluctuations. The oscillation from the output of the wideband amplifier 11 is subjected in the first bandpass limit ™ to 6 to a rigid two-sided limitation, with the result that the signal amplitude fluctuations are eliminated,

and band-pass filtering. The frequency characteristics of the bandpass filter are chosen identical to the frequency characteristics of amplifier 2. Therefore, at the output of the second amplitude detector 7, the time function of the voltage (Fig. 2c) is identical to the function (Fig. 26). in which there are no signal fluctuations. Strictly speaking, with the passage of a useful signal with interference

Q through a band-pass limiter, there is a parasitic phase (frequency) modulation of the interference with the desired signal. However, with strong interference, the parasitic phase modulation is small and causes

5 signal fluctuations at the output of the amplitude detector 7 (Fig. 2b), the relative magnitude of which is from the signal fluctuations at the output of the detector 3 (Fig. 26)

0 value equal to approximately the signal-to-noise ratio at the device input. Thus, the variable voltages at the outputs of the detectors 3 and 7, caused by powerful interference,

 correlated. Therefore, at the output of the correlator 10, a high level of constant voltage is established. In addition to this voltage, a noise component is always present, the value of which is determined by the constant time of the averaging filter of the correlator 10. When the response of the correlator (fig.2g) exceeds the threshold level Uh, the threshold elec

5 ment 9 and key 8 closes. In this case, the voltage from the output of the second amplitude detector 7 is fed to the input of the compensating signal of the compensator 4. In block 4 of the voltage f, the components of the voltage correlated with it are compensated at the signal input of the compensating signal. As a result, the output of block 4 (Fig .2d) there is a selection of signal fluctuations, and the obstruction components are strongly suppressed. The voltage from the output of the limiter 6 is subjected to strict two-sided limiting and band-pass filtering in the second band-limited limiter 1. As a result, the parasitic interference modulation is eliminated, and a high-frequency input of the balanced modulator 5 receives a quasi-harmonic voltage with a constant amplitude and an instantaneous phase equal to the instantaneous phase | interference from the output of the first band limiter 6. In a balanced modulator 5, signal fluctuations (Fig. 2e) are multiplied with a quasi-harmonic reference oscillation, as a result of which the voltage of the recovered useful signal and interference residuals are generated at the device output.

Consider the operation of the device in the second mode, when only the useful signal is valid (the right family of diagrams a, b, c, d, d in figure 2). A low-power useful FM or AM radio signal whose envelope is shown in Fig. 2a is amplified in amplifier 2. After linear amplitude detection by detector 3, the envelope voltage (Fig. 26) is fed to the inputs of the correlator 10 and block 4. In the first band limiter 6, the useful signal subjected to strict two-sided limitation and bandpass filtering with a bandwidth equal to or slightly greater than the width of the signal spectrum. Then, at the output of the limiter 6, a quasi-harmonic voltage with a constant amplitude and an instantaneous phase coinciding with the instantaneous phase of the signal is formed. At the output of the detector 7, a constant voltage (Fig. 2b) is formed, which is uncorrelated with the voltage at the output of the detector 3 (Fig. 26). Then, at the output of the correlator 10 (Fig. 2d), the voltage will be less than the threshold level Un, the threshold element 9 does not work and key 8 is in the open state. The voltage of the envelope of the useful signal from the output of the detector 3 passes almost without distortion through block 4 (FIG. 2d) to the signal input of the balancer of modulator 5, where it is multiplied by the quasi-harmonic voltage from the output of the second band limiter 1. The instantaneous phase of this voltage wives

 equal to the instantaneous phase of the useful input signal. Thus, in the absence of powerful broadband FM interference, the useful signal passes through the device without distortion.

Claims (2)

1. An angular modulation interference suppression device comprising a serially connected narrowband amplifier whose input is an input of the device and a first amplitude detector, a balanced modulator whose output is an output of the device connected in series by a first band stop and a second amplitude detector, unit compensation, the input of the compensating signal of which is connected to the output of the second amplitude detector, and the output is connected to the input of the low-frequency signal of the balanced modulator, about 5 hours Moreover, in order to increase the ratio of the power of the useful signal to the interference power with angular modulation at the output of the device, a second band limiter is inserted in it, the input of which is connected to the output of the first band limiter, and the output is connected to the input of a high-frequency signal of the balanced modulator , the input of the first band stop is connected to the input of the device, and the output of the first amplitude detector is connected to the signal input of the compensation unit. five 2. The device according to claim 1, characterized by the fact that, in order to reduce the distortion of the half-wave signal in the absence of interference with angular modulation, a key is entered into it and a series-connected correlator, the first and second inputs of which are connected to the outputs of the first and second amplitude detectors, respectively, and the threshold element, output The second amplitude detector is connected to the input of the compensating signal of the compensation unit through a switch, the control input of which is connected to the output of the threshold element. interference signal but s s s s s s s s s ABOUT Signal FIG. 2