SU113909A1 - Compatible color television system - Google Patents

Description

This invention relates to compatible color television systems. The main difficulties arising in the development of existing simultaneous compatible color television systems are associated with the need for precise spatial alignment of three color separation images in transmitting and receiving devices, and also the need to transmit two chroma signals in a common frequency band with a third -frequency signal.

The proposed sequential-offset color television system greatly eases these difficulties.

FIG. 1 is a simplified block diagram of a transmitter; in fig. 2 is a block diagram of a receiver.

The system works as follows.

The lens projects the transmitted image onto the photocathode of the transmission tube 2 and simultaneously through the translucent mirror 3 and the drum 4 with light filters onto the photocathode of the second transmission tube 5. The scan in tube 2 is performed in accordance with the parameters of the standard black and white television system (625 lines 50 fields across USSR standard) using a diverting system i. The sweep in tube 5 is carried out in rows with the same frequency as in tube 2, and in half a meter with double frequency. The power of the deflection systems of both tubes is supplied from the sync generator 7, which also generates a voltage of the subcarrier frequency, the value of which is described below. The video signals from tube 2 are amplified by amplifier 8 and fed to mixer 9. Video signals from tube 5 after amplification in amplifier 10 and limiting the frequency band amplitude modulate the subcarrier in modulator 11 and after filter are shifted in mixer 9 with unmodulated signal from tube 2. Full video signal thereafter, the radio transmitter 12 is normally modulated.

In the receiver, the block diagram of which is shown in FIG. 2, the received signals after the radio 13 itself are supplied to

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video amplifier 14 and after it to a conventional single-tube receiver 15. At the same time, the video signals after the radio receiver 13 are fed to a filter and a detector 16, which extracts and detects the modulated subcarrier frequency band. These dedicated signals modulate the electron beam of the color pickup tube 17 and simultaneously arrive at a scan 18. From the main signal (received from the output of amplifier 14, the clock pulses controlling the sweeps 19 and 20 are extracted in the usual way.

The horizontal coils of the diverting systems 21 and 22 of both tubes are powered from the common horizontal frequency (15625 Hz according to the USSR standard), the personnel rolls of the system 21 from the sweep 20 with the field frequency (50 Hz, and the personnel coils of the system 22 from the sweep 18 with a frequency of 100 Hz For the optical alignment of images reproduced on the screens of the tubes 15 and 17, a translucent mirror 23 is used.

The principle of operation of this system is as follows.

Transmitting tube 2 with the sweep parameters of a standard black and white system provides a green color-separated image signal. Transmitting tube 5 operates at the same horizontal frequency, but with a doubled field frequency. The rotating drum 4 is equipped with a series of two types of light filters — blue and red, alternating in turn. In view of this, the number of lines of decomposition in the raster of tube 5 is two times less than the standard number of lines (312.5) and at the same line frequency, the frequency band of the video signal is equal to the frequency band of the signal of the standard system. With the same unsharpness of the image horizontally and vertically (2 elements), the frequency band of the signal from the tube 5 can be made two times smaller than the standard one. In order to confidently separate the frequency spectra after modulation, the frequency band of the blue-red signal is reduced to 0.4 / Mlt., Where the maximum is the standard frequency band of the video signal.

After reducing the bandwidth, the blue-red signal modulates the subcarrier produced by the sync generator 7. This subcarrier is synchronized (in phase or frequency) with the line frequency in one of the known ways in order to ensure its antiphase in adjacent frames and thereby reduce its visibility in black white reception.

The subcarrier frequency is selected in the range of 0.85-0.9 from the value of the highest frequency of the standard black and white signal.

In the receiving device, the tube 15 has a screen of white luminescence, and the observation when receiving color images is conducted through a green light filter 24 shifted when receiving black and white transmissions. The operation of all devices associated with handset 15 is no different from the operation of a conventional black and white TV. The pickup tube / 7 performs a two-color, electrically controlled glow color with color change over the floor m (with a double field frequency compared to the standard black and white television field frequency). It is essential that this tube can have two times less clarity than the tube. / 5 and changing (blue and red) colors.

In the receiving device, the projection principle can be applied. Mirrors 3 transmitting and 23 receiving devices can be both translucent and interference beam-splitting.

The system provides full clarity in green and reduced in two vertical and horizontal clarity in blue and red with full forward and backward compatibility with the standard black and white television system.

The advantages of this color television system compared to purely simultaneous systems are as follows:

Claims (1)

1) in both the transmitting and receiving devices, two rather than three color-separated images are optically combined; 2) the sharpness of the alignment is less critical, since it is not three equally sharp images that are combined, but one clear with the other less clear; 3) the transfer chamber contains two, not three tubes; 4) not three signals are transmitted in the communication channel, but two. Due to this, there is no need for quadrature or two-way modulation of one subcarrier or the use of two subcarriers; 5) due to the use of subcarrier amplitude modulation it is possible ALMOST a complete suppression of the upper sideband and the location of the subcarrier frequency near the upper limit of the channel transmission; 6) subcarrier visibility is reduced on typical black and white TVs due to the high subcarrier frequency; 7) there is no need for synchronous detection of the subcarrier and all subcarrier restoration devices in a color television receiver; 8) the production technology of the color receiving tube is simplified, since it is made two-color, not three-color, and with a definition twice as low; 9) due to the fact that the colored receiving tube works with changing colors across the floor, it can be made single-ended and all the difficulties of combining blue and red images in it disappear; 10) when receiving black-and-white programs on color TVs, only one tube works and there is no loss of clarity inherent in a three-beam tube with a mosaic screen and mask; 11) when receiving in accordance with claim 10, there can be no parasitic staining of a black and white image, characteristic of reproduction on three-beam tubes; 12) the entire system can be synchronized with the frequency of the power supply network and thus provides better compatibility than the system with quadrature subcarrier modulation; 13) it becomes possible to manufacture set-top boxes for black-and-white TVs containing nodes (circled in dotted lines in Fig. 2), which allow receiving color programs on these TVs in colors. Subject invention A compatible color television system, distinguished by the fact that, in order to simplify the equipment and the method of separating the color components of the image, blue and red fields of the image are transmitted at twice the frequency, with the number of lines reduced by half, while maintaining the number of lines and fields for the green component. images. No. 113909 . 2