SU1748268A1 - Method of transmission and reception of stereophonic signal broadcasts - Google Patents

Description

fully submits, and to ensure the possibility of its subsequent restoration, a special pilot tone is introduced into the KCC spectrum with a frequency twice as low as the subcarrier frequency, and tightly coupled with the last one in phase.

The disadvantage of these methods is the possibility of interference through the pilot-tone channel.

In the method closest to the proposed one, the difference signal directly modulates the amplitude of the subcarrier signal, but instead uses partial subcarrier suppression. Together with the subcarrier, the components of the KCC spectrum are attenuated in amplitude and adjacent to it. The characteristics of the circuits implementing this attenuation are strictly standardized. The system can be used both in VHF broadcasting and in television.

The disadvantages of this method are the high level of noise and interference; the coverage area of the transmitter is small (compared to monodivision).

The purpose of the invention is to increase the noise immunity while ensuring compatibility with the stereo system with polar modulation.

This goal is achieved by the fact that in the method of transmitting stereo broadcasting signals, where from the signals of the left and right stereo channels a total signal is generated which modulates the carrier signal in frequency and a difference signal in amplitude in the subcarrier signal frequencies close to it are attenuated in amplitude and the resulting supersonic signal, which is part of a complex stereo signal (CSC), is additionally modulated in frequency by the carrier signal; The signal is transmitted to the communication channel, after which the received signal is demodulated, extracting the signals from the left and right stereo channels, the supersonic signal on the transmitting side is obtained by summing two quadrature components, one of which is a normal supersonic part of the complex stereo signal with a partially suppressed signal. subcarrier in a system with polar modulation, and the other is obtained by pre-compression of the dynamic range of the difference signal and the subsequent attenuation in it of the amplitudes of low-frequency components, and this attenuation is performed according to the same law as for the normal, non-compressed, differential component, as well as adding to the compressed signal an infrared identification signal and performing the balanced modulation of the quadrature subcarrier component, and on the receiving side, the sum and difference signals are separated, and the amplitudes of the low-frequency components of the difference signal are successively restored and which by means of sum-difference conversion, from the obtained sum and difference signals, the signals of the left and right stereo channels are extracted.

FIG. Figure 1 shows the KCC spectrum modulating a carrier in a system with polar modulation; in fig. 2 shows the KCC spectrum formed with the proposed method for transmitting stereo broadcasting signals: FIG. 3 - an example of the implementation of the proposed method.

From the comparison of FIG. 1 and 2, in the second case, the modulating frequency spectrum contains all the components of the traditional KCC and, in addition, the additional components — the products of amplitude modulation by the compressed difference signal Us1 of the quadrature subcarrier component. At the same time, the quadrature component itself is suppressed completely, and the supersonic components nearby to it — the products of its modulation — are partially attenuated in amplitude. The law of this attenuation is chosen the same as the law of attenuation of the corresponding components in the traditional CIL. This makes it possible to simplify the construction of a stereo decoder at the receiving end, improve compatibility with the usual method of stereo broadcasting, and unify a number of nodes in traditional and prospective stereo decoders.

When transmitting stereo broadcasting signals, the signals Ua of the left and UB of the right stereo channels from the input of the stereo module 1 are sent to the summing-subtracting unit 2, from one of the outputs of which the difference signal Us is fed to the input amp-. of the modulator 3 and the compressor 4. From the output of the latter, the compressed signal Us1 is fed to the input of the balanced modulator 5. The amplitude 3 and balanced 4 modulators are controlled by the signals of the subcarrier frequency and 90 ° shifted in time with each other relative to each other by a quarter subcarrier period, taken from the two outputs of the generator b subcarrier. The modulated signals 11am and 1) bm of the subcarrier from the outputs of amplitude 3 and balanced 5 modulators are fed to two inputs of adder 7, to the third input of which

from the output of the summing-subtracting device 2 comes the signal UM. To the fourth input of the adder, an identification signal from the generator 8 is applied. From the output of the adder 7, the signal arrives at the input of the suppressor 9 subcarrier. similar to the corresponding device in a system with polar modulation. The complex stereo signal UK, which is formed at the output of block 9, is fed to the input of the radio transmitting exciter to the radio station 10, frequency-modulates the carrier of the transmitter and is transmitted by means of the antenna 11.

At the receiving side, a high-frequency signal received by the antenna 12 is processed by the receiving device 13, from the output of the frequency detector of which a dedicated complex stereo signal is fed to the input of the stereo decoder 14. In the KCC stereo decoder, through the restorer 15, the subcarrier enters one of the inputs of the synchronous detectors 16 and 1 simultaneously to the synchronization input of the generator 17 subcarrier. the signal-forming subcarrier frequency 0C 0, and shifted in time with respect to each other by a quarter of the subcarrier period. From the outputs of the generator 17, these signals are fed to the other inputs of the synchronous detectors 16a and 16. At the output of the detector 16a, an uncompressed difference signal is released and $ ordinary. transmitted on the in-phase subcarrier component and used in normal stereo transmission. Via key 19a, the signal is normally transmitted to one of the inputs of summing-subtracting device 20. At the output of synchronous detector 16, a compressed difference signal Us1 is extracted. Through the expander 18, restoring the initial dynamic range of the signal Us, due to which the noise level and noise of the difference signal are attenuated, this signal goes to the identification signal extraction circuit 19 and through the key 19a to one of the inputs of the summation-subtractor 20 . The second input of the last from the input of the stereo decoder receives the signal UM. part of the KCC. The UA and UB signals, taken from the outputs of the summing-subtracting device, through the filters of the 21 lower frequencies are fed to the amplifiers of 22 audio frequencies.

When conducting stereo transmissions according to the proposed method, the difference input of the summing-subtracting device 20 must be switched from the output and the $ ordinary synchronous detector 16a to the output Us of the expander 18 using a key 19a, controlled either manually or with

using the identification signal UH allocated by the node 19. The same signal can also serve to identify the transmission mode (indicator 19 b).

All blocks, except for compressor 4, expander 18, identification signal generator 8, and identification signal extraction device 19 on the receiving side, included in a stereo module (2, 3, 5-7) or a decoder (5, 16, 17, 20), performed traditionally.

The identification signal generator 8 can be performed by any of the known schemes, for example, the Winn Bridge.

The identification signal extractor 19 is a conventional narrowband filter (or low pass filter) and a rectifier. Compander noise reduction devices are widely used in broadcast and consumer radio equipment. The compressor 4 and the expander 18 used in the proposed method do not have fundamental differences from those used in other systems. In order to suppress and restore the subcarrier signal in the proposed method of transmitting stereo broadcasting signals, any schemes and devices suitable for generating and decoding a CSS in a polar modulation system can be used. Transmitting and receiving devices, antennas (10-13), as well as terminal devices (21, 22) are built according to known schemes.

The technical effect of using the proposed method is to significantly reduce the level of noise and noise during stereo reception. In the existing stereo system, this level is mainly determined by the reception quality of the component Us and exceeds the corresponding level for mono reception by 20-24 dB. With the proposed method, this difference will be no more than 2-4 dB, respectively, the area of high-quality stereo reception signals will expand several times.

Claims (1)

Invention Formula The method of transmitting and receiving stereo broadcasting signals, which consist of summing up and difference signals from the left and right channels on the transmitting side, the last of which amplitude modulating the subcarrier frequency signal, forming the supersonic part of the complex stereo signal by attenuating the amplitude modulated signal in the subcarrier, the supersonic part of the complex stereo signal is summed with the sum signal and the received signal The carrier signal is transmitted in frequency, which is transmitted over the communication channel, and at the receiving side, the received signal is demodulated in frequency, the total signal and the supersonic part of the complex stereo signal, which is demodulated to form a difference signal, are extracted, and together with the total signal, the total difference signal is performed. conversion, extracting left and right channel signals, characterized in that, in order to increase noise immunity while ensuring compatibility with the stereo broadcast system with polar modulation, on the transmitting side the differential signal is subjected to compression followed by attenuation of the low-frequency components, summed with the infrasonic tonal signal and the resulting signal is balanced by modulating the quadrature component of the subcarrier frequency signal, after which the demodulation is entered into the supersonic part of the complex stereo signal by summing it with the latter signal on the receiving side the quadrature component of the supra-sonic part of the complex stereo signal is carried out by synchronous detection, and the formation of difference The signal is accomplished by restoring the amplitudes of the low frequency components, expansion and synchronous detection. U U Sh tar. I tor. 2 Fig.Z