Color TV receiver

1. How are signals transmitted

The following 4 signal are included in electric wave of one channel which is transmitted by broadcasting stations.
- Picture signal
- SYNC signal
- Color signal
- Sound signal
They consist of picture sìgnal, which pick up video signal out of transmitted from broadcasting station and catch it by antena, circuits of synchronization and deflection, which compose pictures, circuits of color sìgnal reproduction.

2. Operation of each block
3. Circuit of video signal
》3.1 Tuner
Tuner operates to selec necessary wave out of some TV electric wave , amplify it, and convert it into intermediate frequency signal ( 58.75MHz for video, 54.25MHz for sound ). Tuner of input tuning, high frequency amplification, mixture and local oscilation. And is classified into VHF use according to receiving frequency band.
Assuming that chanel 1 is comes through antena, video carrier is 91.25MHz and sound carrier is 95.75MHz.While chanel 1 is received, local oscillating by 150MHz.
>>150MHz ― 91.25MHz = 58.75MHz
>>150MHz ― 95.75MHz = 54.25MHz

3.2 Automatic frequency setting ( AFS ) circuit
This circuit is to prevent oscillation frequency at local oscillator of tuner from drifting by change of temperature , it operates to detect the deviation of picture intermediate frequency of 58.75MHz, generate control voltage and apply it to variable capacitance diode, consequently correcting oscillation frequency.

3.3 Picture intermediate frequency ( picture IF ) amplification circuit
This is composed of 3 and 4 step tuning amplifier, where most part of gain which is necssery for received is obstainf.
3.4 Picture detection circuit
Is circuit operates to pick up composite video signal out of video intermediate frequency whic amplified by picture IF amplification.Composite video signal is a composite signal consisting video ( brightness ) signal , SYNC signal, chrominance carrier video.

3.5 Video amplification circuit
Is circuit operates to amplify composite video signal and signal for picture tube. It requires wide band characteristic to evenly frequency from direct current to nearly 4MHz.This circuit also has supplementary circuits such as delay element to video signal and chrominance signal in time, contrast, brightness and picture quality.

3.6 AGC ( Automatic Gain Control ) circuit


TV design section