Block Diagram of Black and White Television
According to the Block Diagram of Black and White Television Sets In a typical black and white television receiver, the signal from the antenna is fed to the tuner. Two channel selector switches – one for the VHF (very-high-frequency) channels 2-13 and the other for the UHF (ultra-high-frequency) channels 14-69 -are used. They connect circuits that are tuned to the desired channels and, also discriminate against signals from undesired channels. These circuits also form part of an amplifier, designed to add as little snow to the signal as possible.
The amplified signals from the desired channel are then passed to the mixer, which transposes all the signal frequencies in the channel to different values, called intermediate frequencies. The output of the tuner consists of all the signals in the desired channel, but the intermediate channel is fixed in the frequency band from 41 to 47 MHz, no matter what channel is tuned in. This is kind of like those cable television "set top" converters, that, regardless of what channel you’re watching, always convert it to "channel 3" for your TV set.
From the tuner, the 41-47 MHz channel with all picture and sound information present is passed successively through several additional amplifiers (from two to four intermediate frequency, or IF, amplifiers), which provide most of the amplification in the receiver. Their amplification is automatically adjusted, being maximum on a weak signal and less on a strong signal. So far the receiver handles the signals in the channel just like they would be received from the transmitter, except for the shift to intermediate frequencies and the amplification.
The next stage is the video detector, which removes the high frequency carrier signal and recovers the video signal. The detector also reproduces (at a lower frequency) the sound carrier and its frequency variations. The sound signal is then separated from the picture signal and passes through a frequency detector, which recovers the audio signal. This signal is amplified further and fed to the loudspeaker, where it re-creates the accompanying sound. The picture signal from the video detector is used in the normal fashion for display on the CRT of the television receiver.