Transmitter and Receiver Circuit

COLOUR TV TRANSMITTER

The technology development  taken as many changes which we can in many ways  the black and white vision is non colour which describes the no primary colour in TV.

The tv transmitter Now how we can see clour tv in different stimualtion waves 

and how it works in TV, with colour mixing  with colour camera.

TRANSMITTER (tx):

The scene to be televised is separated into R,G,B using camera. The luminance signal  "Y" and chrominance signals R-Y  and  B-Y  are obtained using suitable colour matrix. the two colour difference signals are passed through low pass filters to limit their bandwidth at about 11.5Mhz. in this process the signals experince some dealy compared to Y  signal . therefore a dealy line is inserted inthe luminancw signal "Y" path to compensate this dealy

 Transmitter and Receiver Circuit

The colour surator generates  in 4.4Mhz carrier and fed directly to "B-Y" modular  these signals are added to yield the quadrature  amplitude modulated chrominance signal. the "C" signal is combined with "Y" signal to get composite  colour video signal .

then this signal is processed amplified and modulated using suitable carrier  .this signal after proper amplification  and addition of the sound signal will be radited in to space using antenna.

COLOUR TV - RECEIVER(Rx):

The signal is received using the antenna .the tunner will tune the corresponding channel and gives the video in IF. This IF signal after  amplification fed to video detector and video amplifiers ,from this stage the intercarrier IF is separated  and fed to sound section .here the intercarrier sound IF signal is ampilfied detected and gives to audio amplifier for further amplification .then the sound signal is reproduced using loud speaker.

The video detector  output consists of  Y  signal , c signal  and sync pulses . Y signal is delayed using delay line  and fed to matrix . the C signal is fed to B-Y detector  and R-Y detectors. the colour brust  signal is separated and colour subcarrier is generated .this colour subcarrier is fed to B-Y detector and through phase  reverse switch to the R-Y detector . these colours deference signal  added with Y signal and generates RGB signals  and fed  to tricolour pictures tube.

the sync pulses are separeted  and fed to vertical & horizontal deflection circuit to generate  deflection current to deflect the electron beam .EHT (Extra High voltage Transformer.) generated from

horizantal amplifier  and is given to picture tube.

COLOUR PICTURE TUBES:

Colour picture tubes are based  on the principle of additive colour impression by the eye.The phosphors are exited by three electron beams intensity modulated with corresponding RED ,GREEN & BLUE, Signals . The three beams simultaneously scan the phosphor screen keeping their alignment on to the respective colour phosphors ,during the entire scanning process .there are three basic desgins of colour picture tubes . these are  below :

1) DELTA GUN COLOUR  PICTURE TUBE .

2) THE  THREE GUN IN LINE  TYPE OR PRECISION IN LINE  PICTURE TUBE.

3) SINGLE  GUN OR TRINTRON  COLOUR PICTURE TUBE.

CRT TUBE 

CRT-based VGA displays use amplitude-modulated moving electron beams (or cathode rays) to display information on a phosphor-coated screen.

LCD displays use an array of switches that can impose a voltage across a small amount of liquid crystal, thereby changing light permittivity through the crystal on a pixel-by-pixel basis. 

In a black & white video camera the image comes through the lens and onto the sensor which generates a video signal representing the image. In a colour video camera, after coming through the lens the signal is split into three different colours (red, green and blue) through prisms. These coloured images then each go to a separate sensor, generating three separate video signals, one with the red picture information, one with the green picture information, and one with the blue picture information.  These three separate video signals (Red, Green and Blue) is what is known as RGB video. It is the most pure form of analogue colour video signal.

RGB PRISM 

As well as the three full coloured signals, there also needs to be the timing information to make up picture. We need to appreciate that although a TV picture looks like it is a continuously moving picture, it is actually a series of still pictures (called frames) changing 25 or 30 times a second – and this looks like a continuously moving picture to our eyes. Each frame (still picture) is made up of lots of horizontal lines (525 or 625 lines). All these lines and frames need to be kept in time, or in sync, hence these timing signal are called horizontal sync (H) and vertical sync (V).

Some RGB video signals combine the sync signal with the green coloured picture and some have separate cables for each, requiring 5 signal paths in total.

Cables to Use for RGB Video:

Scart connectors are widely used in Europe. They are convenient as the video and audio are connected through the one plug, reducing the confusion from having to plug in three video cables and two audio cables.

he standard VGA (Video Graphics Array) plug has been used to connect computers to monitors for many years. They have 15 pins and carry the three RGB coloured signals and separate H sync and V sync. 

This is the best quality analogue colour signal that a computer can produce. VGA is now the generic term used for this type of plug and cable – it was originally introduced by IBM.  Good quality VGA cables can be run up to 50 metres (150 feet). Longer cable runs can use 5 seperate RG59 coax cables. Note: VGA cables only carries video signals, separate cables are are required for audio.

Problems with RGB Video:

RGB video may well be the purest form of analogue colour video available, but it is a lot of information to be processed and stored. Remember it is three complete picture waveforms. Therefore it is not easily stored, especially by domestic recorders.

In the next article, we will discuss component video, and see why it is often used in domestic and commercial AV installations.