SU771890A1 - Device for receiving signals with suppressed carrier frequency - Google Patents

Description

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The invention relates to communication and can be used in apparatus for receiving discrete information transmitted by means of phase-shift keyed signals. 5

A device for receiving signals from a suppressed carrier is known, which contains a matched filter, a loop filter and a control: an oscillator, the output of which is connected to the first input 10 of the signal converter in video frequency (quadrature).

However, the known device has a relatively low noise immunity .15

The aim of the invention is to improve noise immunity.

To do this, a device for receiving signals from a suppressed carrier, containing a matched filter, a loop filter and a controlled oscillator, the output of which is connected to the first input of the video signal converter by quadrature components, has two switches, a generator 25, a threshold unit, a frequency error sensor, a frequency error signal extraction unit and an adder. The output of the adder via the control generator is connected to the first input 30

frequency error sensor, the second input of which is connected to the output of the reference generator and one input of the first switch, to the other inputs of which are connected, respectively, the output of the matched filter and the output of the threshold unit connected to one input of the second switch, the outputs of which are connected to the inputs of the loop filter and the signal extraction unit frequency error, the output connected to the first input of the adder, to the second input of which the output of the loop filter is connected, the output of the first switch and the other input second switch are connected correspondingly with the second input transducer and the output signal of the quadrature videochastotny comprised between, and the output frequency error detector connected to the input of the threshold unit.

The drawing shows a structural electrical circuit of the proposed device.

A device for receiving signals from a suppressed carrier contains a matched filter 1, the first switch 2, the reference generator 3, the transducer / 4 signals in the video frequency

The quadrature components software, the second switch 5, the adder 6, the loop filter 7, the frequency error signal extraction block 8, the controlled oscillator 9, the frequency error sensor 10 and the threshold block 11.

The device works as follows.

If the frequency difference between the controlled generator 9 and the reference generator 3 is less than a certain threshold value U о, the threshold unit 11 connects the matched filter 1 to the converter 4; if this difference is greater than the threshold value F., then the threshold unit connects the reference generator 3 to the converter 4, i.e. the input signal is connected to the device only when the detuning between the suppressed carrier and the controlled generator becomes so small (UF) that the false loops of the loops of the phase-locked loop frequency formed by the transducer 4, the loop filter 7, and the controlled oscillator are eliminated.

Initially, when the detuning is greater than d F, 2in sensor 10 generates an error signal greater than the threshold (D Fiin) D threshold block 11, the output of which is a control signal, acting on switches 2 and 5 so that it connects the output of the reference generator 3 to the second the input of the converter 4, and its output to the input of the block 8. The block 8 operates in such a way that at its output a DC signal is generated, the level and polarity of which are determined by the sign and magnitude of the difference of the frequency. The one between the controlled oscillator 9 and the reference oscillator 3. In this case, the input signal of the block 8 is the beat voltage at the output of the transducer 4, This beat voltage contains information about the sign and magnitude of the frequency difference.

Thus, connecting the block 8 through the adder 6 to the controlled oscillator 9 allows forming a frequency-locked loop (CHAP) for the frequency of the reference oscillator 3 and reducing the minimum frequency detuning of the controlled oscillator relative to the reference oscillator to a minimum (less than b). This effect is achieved. Even with very significant frequency instability of the controlled oscillator, since the CHAP ring works without interference and its statism can be quite high.

After the detuning becomes less than Л,, the threshold unit 11 switches the switches 2 and 5 so that the output of the PgServe filter 1 is connected to the second input of the converter 4, and the output of this converter through the loop filter 7 and the adder b to the controlled generator 9. V As a result, the adjustment to the input signal begins at very small detunings of the controlled oscillator relative to the frequency of the reference oscillator 3, i.e., and relative to the suppressed input signal carrier. This ensures the release of the suppressed carrier without any false hooks: the error signal from the output of converter 4 is fed to the loop filter 7, and from its output through the adder b to the controlled oscillator 9. In this case, if block 8 has a time limited memory , the voltage at its output gradually decreases to zero: the time constant of this process can be made very large. However, due to the fact that the phase locked loop is in the hold mode on the input signal, the voltage disappearing from the output of the block 8 is compensated by appearing the corresponding voltage on the output of the loop filter 7. If no useful signal is applied to the device input, the hold mode no, the controlled oscillator 9 is detuned in frequency with respect to the reference oscillator 3, which leads to a difference of frequencies exceeding l F and switching the device to the initial tuning mode for the reference oscillator.

The proposed device allows to provide a constant readiness for signal reception without the occurrence of false captures, which guarantees the work on the signal with increased noise immunity.

Claims (1)

1. Linda, Cymen. Characteristics of the automatic frequency control schemes intended for the coherent detection of signals with a reduced carrier in the presence of detuning in frequency. TSIER, 9, T. 58, M., Mir, 1970, p. 19-26 (prototype).