Television principle
Television is mainly composed of tuner, audio head, audio channel, common channel, synchronous scanning channel, color control display and power supply. It works as follows.
The signal received from the antenna passes through the tuner, selects the high-frequency TV signal, amplifies it, and then sends the fixed intermediate-frequency TV signal.
The common channel consists of an IF amplifier, a video detector, a video amplifier and a picture tube. The IF amplifier amplifies the IF signal from the tuner to a sufficient amplitude, which is detected by the video detector, removes the IF carrier, recovers the image signal, and converts the second audio IF signal.
After the video is amplified, the image signal is sent to the cathode emitting electrons in the picture tube to control the aggravation of the electron beam emitted by the picture tube, and the image can be displayed on the screen.
The second audio intermediate frequency signal enters the audio channel for amplification, and the audio synchronous scanning channel released by the speaker mainly produces field scanning and line scanning signals. The line scanning signal makes the magnetic field generated by the deflection coil sleeved on the picture tube control the electrons emitted by the cathode of the picture tube to scan the screen from the upper left corner to the upper right corner, scan the first line, then scan the next line, and scan the whole screen for 625 lines.
The field scanning signal controls the deflection yoke, so the image has 25 fields per second. Because there are actually 2×25=50 interlaced scans per second, and the scanning positions of line and field light spots are the same as when the TV camera tube is facing the scene, the outline of the scene and the brightness of each part of the scene can be presented on the screen.