The block diagram of a TV communication system consists of a TV transmitter and a receiver. In this section we will understand the working of block diagram of TV communication completely.
The below figure shows the TV broadcast transmitter.
- There are two sections of the transmitter unit.
- One unit is responsible for generation of video signals. This unit receives pictures and based on them it generates the video signals.
- This video signal then helps to modulate the Radio frequency signal. The antenna further transmits this signal.
- The other unit generates an audio signal which contains information in the form of sound. This signal then modulates another RF signal.
- We use only one antenna for both transmission and reception of signals.
- Now there mixing of these two video and audio signals.
- We require an amplifier to amplify these audio and video signals before they could modulate their respective RF carriers.
- The audio and video amplifiers help in amplification.
- We use an AM transmitter for Amplitude Modulation of video signals.
- Whereas we use FM modulators for frequency modulation of sound information.
- The scanning of electron beam from the actual picture through a scanning circuit which produces corresponding video signals.
- At the receiving end also the same process is used.
- Hence, we need synchronizing circuits at both transmitting as well as receiving ends,
- The transmission section of the broadcast unit is has two main sections.
- One which modulates the amplitude (video) and another which modulates frequency (audio).
- For generating RF signal frequency we use Master oscillator. This master oscillator generates sub multiple carriers.
- These carriers then drive frequency multipliers for obtaining the correct value of carriers.
- The Class C tuned amplifiers are harmonic generators.
- A buffer exists between the master oscillator and harmonic generator.
- The carrier of the video transmitter is fed to AM and also to FM in the audio transmitter.
- As the amplification is of low level, linear amplifiers amplify these modulating signals.
- The video and audio signals are separately produced. They are combined and then fed to the transmitting antenna.
- The receiver end produces back the images from the amplified signals received at the receiving antenna.
- The receiver circuit amplifies and converts video and audio RF signals into visual images with their audios.
- The images generated can be colored or black and white.
- To fulfil this purpose the superheterodyne receivers which simultaneously amplifies and converts audio and video RF signals.
- The tuner picks up the required signal and then converts it to a lower frequency.
- This frequency is in between the intermediate frequency pass band.
- An amplitude detector, video amplifier and intermediate frequency amplifier forms a signal processing unit.
- There is a color processing circuit for chrominance signals.
- The control electrodes of the kinescope receive a brightness signal and color difference signals.
- The extraction and decoding of chrominance signals is in color processing circuits.
- The horizontal and vertical scanning circuits form a scanning generator unit.
- For exciting purposes, an electron gun kinescope interface has static and dynamic white balance controls. They also regulate the focusing beam.
- There are different amplifiers for amplifying frequency in the audio section.
- The power supply section will convert the main supply voltage into the supply voltage for the TV set.