SU832748A1 - Stereo decoder - Google Patents

Description

(54) STEREODECODER

I

The invention relates to radio engineering and can be used in broadcasting stereo receiving equipment with polar modulation.

A stereo decoder is known that contains a series-connected first signal multiplier, a first low pass filter and a DC amplifier, successively connected second signal multiplier, a second low pass filter, a threshold unit, and a first key whose other input is connected to the first input of the second signal multiplier, and also a stereo detector, the first input of which is connected to the output of the first key, while the first input of the first signal multiplier is connected to the second input of the second signal multiplier signal als and a second input stereodetektora 1 J.

However, the well-known stereo decoder possesses a good channel separation of i-noise immunity. Only when working with PSH1TOTON, when working with

by a polar modulated signal, its noise immunity drops sharply due to the possibility of synchronization of the controlled oscillator to the overtoneff i ie signals that are close in frequency to the subcarrier signal.

The purpose of the invention is the behavior of noise immunity.

This goal is achieved by the fact that in a well-known stereo decoder, containing a serially connected first signal multiplier, a first low pass filter and a DC amplifier, a second signal multiplier connected in series, a second low pass filter, a threshold unit and a first key, the other input of which is connected with the first input of the second signal multiplier, as well as the stereo detector, the first input of which is connected to the output of the first key, with the first

The input of the first signal multiplier is connected to the second input of the second signal multiplier and connected to the second input of the stereo detector, the RC filter and the second and third keys are inserted, while the output of the DC amplifier is connected to the first input of the RC filter, the first output of which is connected to the second input of the first signal multiplier, the output of the threshold unit. connected to the first inputs of the second and third keys, the outputs of which are connected respectively to the second and third inputs of the RC filter, the second output of which is connected to. th entry of the first key the first input of the first multiplier sinalov connected to the second input key has invaded, and the third RC-filter output is connected to the second input of the third switch.

The drawing shows a block diagram of the proposed device.

The stereo decoder contains the first signal multiplier 1, the first low pass filter 2, the amplifier 3 DC, the second multiplier 4 signals, the second low pass filter 5, the threshold unit 6, the first switch 7, the stereo detector 8, RC filter 9, the second switch 10, the third key one.

The stereo decoder works as follows.

In the absence of a stereo signal at the output of the RC-filter 9, there is no signal and therefore the first key 7 is open. The outputs of stereo detector 8 are identical mono signals. ,

When a phon-modulated sig hanai appears at the stereo decoder's input, the resonant frequency of the rc filter 9 is synchronized in frequency and phase with the frequency of the subcarrier signal due to the operation of the phase-locked loop consisting of the first multiplier 1 signal, the first filter 2 of the lower frequencies booster

3 DC current and RC filter 9, the signal from the first output of which is fed to one of the inputs of the first multiplier 1 of signals. After this circuit captures the subcarrier frequency at the inputs of the second multiplier

4 signals are supplied by an input polar-modulated signal and a signal from the second output of an RC filter 9 which differs in phase

90 from the first output signal.

In this case, at the output of the second multiplier 4 signals, a signal appears, which passes through the second low-pass filter 5 re-throws the threshold unit 6, which causes the third key 11 to open and the first and second keys 7 and 10 to close.

 Thus, the input modulated signal is turned off

from the input of RC-FASHI 9, and the filter itself., due to the fact that the second key 10 closes the positive feedback loop, is introduced into the self-excitation mode at the subcarrier frequency

signal without breaking the synchronization mode in frequency and phase with the subcarrier signal. The signal from the second output of the RC-filter 9 is fed to one of the inputs of the stereo detector 8, which directly detects the signals of the stereo channels. ,

Thus, in the proposed stereodecoder, the possibility of capturing the over-tone frequency instead of the subcarrier is practically eliminated, with wide capture and synchronization bands, i.e. noise immunity increases.

Claims (1)

1. M.I.Gay A monolitic phase lock - loop stereo decoder, WEEE on BTR, vol. 17, No. 4, 1971, p. 270-276 (prototype).