SU375802A1 - DEVICE FOR DEMODULATION OF FREQUENCY MODULATED SIGNALS - Google Patents

Description

one

The invention relates to the field of reception of frequency-modulated (FM) signals, namely, devices for demodulating FM signals with increased noise immunity.

A device for demodulating FM signals is known, comprising an anomalous noise pulse detection and compensation circuit connected between the frequency discriminator output and the low-pass filter input. This circuit consists of a matched filter, two threshold blocks connected to the output of a matched filter, a pulse driver, the inputs of which are connected to the outputs of threshold blocks, and an adder, one of the inputs of which is connected to the output of the driver of pulses. However, this device has low noise immunity.

The aim of the invention is to improve the noise immunity of the device.

This is achieved by the fact that the device is equipped with n series-connected detection and compensation circuits for anomalous noise pulses (where n I, 2, 3, ...), and in each detection and compensation scheme the second adder input is connected to the filter input, the frequency characteristic of which is matched with an energy spectrum of abnormal pulses.

The drawing shows a block diagram of the device.

The device contains a filter / intermediate frequency, limiter 2, frequency discriminator 3, n series-connected detection and compensation circuits 4 for abnormal noise pulses and a low-pass filter 5.

Each of the schemes for detecting and compensating abnormal noise pulses consists of a matched filter 6, threshold blocks (for positive pulses 7 and for negative pulses 8), a driver 9 for compensating pulses, and an adder W.

The device works as follows.

An input signal representing the sum of the frequency modulated signal and noise is fed to the input filter / intermediate frequency. From the output of this filter, the signal is fed to the input of limiter 2 and then to the input of frequency discriminator 3. The output signal of frequency discriminator 3 is fed to circuit 4 for detecting and compensating for abnormal pulses, a matched filter 6 passes, the output of which is fed to threshold block 7 to detect positive anomalous pulses and a threshold block 8 for detecting negative anomalous pulses. When the threshold blocks 7 and S are triggered, the compensating pulse driver 9 generates a pulse, the polarity of which is determined by which of the threshold blocks has tripped. The output slots of the frequency discriminator 3 and the pulse driver 9 are added to the adder 10.

After the first stage of detection and compensation, the signal from the output of the adder enters for further processing into such a further detection and compensation scheme several times. The signal from the output of the last adder 10 is filtered by low pass filter 5.

As a result of adding to the output signal of the frequency discriminator of the compensating pulses, the energy of the anomalous pulses is transferred to the high-frequency region and eliminated by a low-pass filter.

Two to three detection and compensation stages are sufficient for the efficiency of the proposed device, since the probability of occurrence of n closely spaced anomalous pulses rapidly decreases with increasing n.

When cascade detection and compensation of abnormal pulses for normal operation of the device, the energy spectrum of the compensating pulses must be equal to the energy spectrum of the abnormal pulses. When using only one cascade of detection and compensation, the shape of the compensating pulses is not significant. In that

In this case, it is only important that the pulse duration be significantly shorter than the pulse response time of the low-pass filter.

The threshold for triggering threshold blocks 7 and 8 is chosen from the condition that the probability of missing abnormal pulses of probability is equal;

Subject invention

A device for demodulating frequency-modulated signals, comprising an anomalous noise pulse detection circuit between an frequency discriminator and a low-pass filter, which consists of a matched filter switched on at its input, two connected to it

the output of the threshold blocks, the pulse generator, the inputs of which are connected to the outputs of the threshold blocks, and an adder connected by one of its inputs to the output of the pulse generator, characterized in that

that, in order to improve the noise immunity of the device, it is equipped with serially connected analogous schemes for detecting and compensating abnormal noise pulses, where n 1,2, 3, ... and in each detection and compensation circuit of abnormal noise pulses the second input of the adder is connected to the input of the matched filter.

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