Television

A television of

television is the transmission, by cable or radio waves, of images or animated and generally wired for sound scenes which are reproduced on a called receiving set television set, progressively with the reception. The first stages of the remote vision by electricity are it télectroscope then television.

The following text is a summary of articles published in the "Bulletin of the Committee of history of television", N° 23 (June 1991) and 24 (March 1992) : Television is a means of diffusing by an electrical current (line) or by a wave (hertzian way), in a sequential way, the elements of an image analyzed point by point, line after line.

At the origin, a mechanism allowed the exploration of a whole of electric eyes (mosaic). Later, the sweeping (scanning) of the mosaic will be carried out by a mean electron beam (analyzes cathodic).

First mosaic made up of elements of selenium was described, in , by George R. Carey, one American of Boston.

The principle of sweeping appears in , in a project of "télectroscope" of Constantin Senlecq, notary in : a mechanism of pantograph explore the back face of dulled glass on which the image of an object is projected.

A portable television

In , a German engineer deposits a patent of "electric telescope" (Elektrische Teleskop). A disc, bored with its periphery of holes laid out according to a centripetal spiral, analyzes while turning the brightnesses of a line of the image transmitted by an objective. The shift of the holes makes it possible to pass from one line to the other.

In these various cases, the reversible character of each process must ensure the reproduction of the image.

In , one , Boris Rosing deposits a patent which proposes to use a sophisticated cathode ray tube in by Ferdinand Braun, to reproduce an image analyzed by electromagnetic means.

The following year one , Campbell-swinton, proposes the use of the cathode ray tube to the analysis and the reproduction of the image.

None of these projects mentions the reproduction of the movement.

These projects will lead a Russian emigrated to the United States, Wladimir Zworykin, to deposit in a "very electronic" patent of television (all electronic). The difficulty of showing the use of it practises will differ fifteen years approval from it.

History

: First transmission of images (fixed) per electric way carried out by Caselli with a baptized apparatus pantélégraphe.

: The German Paul Nipkov invent it Disc of Nipkov. This system of analysis of the image was based on a disc perforated turning with 25 turns a second. Each hole, 30 to 200, is placed at a decreasing distance of the center, which makes it possible to analyze the image line by line. The image is then made up of as many lines as the disc is bored holes.
- One photocell recover light who passes by the holes of the disc to transform it into signal electric ;
- With the reception, an identical system, a tube with neon replacing the electric eye and a revolving disc at the same speed restores them images.

But they are progress in which will allow the transmission of images of quality.

: Invention by Lee de Forest first electron tube, triode, device at the base of any sophisticated electronic circuit.

: The Russian Boris Rosing invent it cathode ray tube, which makes it possible to post an image by the sweeping of one electron beam on a surface phosphorescent.

: The Russian Wladimir Kosma Zworykin invent itviewfinder. It acts of the first electronic analyzer of image allowing a high definition. This type of sensor was used until the generalization of sensor CCC.

: , itScottish John Logie Baird carry out the first public demonstration of television in a store of by using a sensor by disc of Nipkov. The definition is of 30 lines and the image measures 3,8 out of 5 centimetres. The inventor shelled had completed his work in its laboratory in October .

: John Logie Baird carry out the first tests of television in color.

: First regular emissions of television in .

: First regular emissions of television in on 30 lines.

: There are 400 to 500 television receivers in .

: First emission in 180 lines since Eiffel Tower.

: First television receiver with cathode ray tube.

: Regular emissions of television since the Eiffel tower.

: Emissions in 445 lines since the Eiffel Tower.

: First experimental system of television color.

: Beginning of the emissions in 819 lines since the Eiffel tower.

: First emission of télévion color in public with in NTSC.

: Television receiver Premièr color The "CT-100", left it of the workshops of RCA and equipped with a screen with 30 cm.

: First professional apparatuses ofvideo recording.

: Launching of satellite Allowing TELSTAR 1 of the retransmissions TV deck chairs.

: First emissions of television in Tunisia.

: First emissions of television color SECAM in France.

: First video tape recorders with cassettes.

: Experiments of the system of teletext Antiope.

: Arrival of the video tape recorders in France.

: Creation of the standard MAC by the British.

: Adoption of the format of image 16/9.

: First receivers D2-MAC for general public.

: Diffusion of the OJ ofAlbertville in HD-MAC.

: First numerical bouquet of TV by satellite in the USA.

: Numerical television by satellite in France.

2004 : Numerical television by ADSL.

2005 : Startup of Terrestrial numerical television (TNT) in France. March 31, 2005: 35 % of the French population are covered.

Reception

Work completed within the framework of the TPE in 2005 in a college of Aisne by a group of Terminal S Ing (of which Leonsulivan)

Principle

The guiding principle of the reception of the television set is extremely simple: it is enough to an antenna which will be connected directly to the transformation part of the wave into image, because it is enough in theory to a simple antenna to receive information.

However, this is only theoretical bus indeed many parameters prevent this system simple to function. The first being in addition impossibility of receiving sound.

Demodulator

Treatment of the emitted wave

The first encountered problem is about the emission. Indeed, it is very difficult to send the signal on a long range just as it is.

The second problem is impossibility in this case of receiving several channels.

To solve these two problems simultaneously the method used is to integrate the video signal into a carrier wave.

Signal

<center>+

Carrying

There are two ways of integrating the signal into the carrier wave. First is by amplitude and second is by frequency.

Amplitude modulation

Frequency modulation

The integration of the signal is done by amplitude for the video, whereas it is done by frequency for the sound, which makes it possible to join together these two elements on the same carrier wave.

There is however a tiny difference between France and the rest of the world, namely that France integrates by positive amplitude (a peak on the signal of origin will correspond has a "hollow" on the modulated signal) whereas all the other standards use the negative amplitude modulation. The principal difference in these two techniques intervenes at the time of appearance of parasites. For example, in France a parasite will be white whereas in the rest of the world it is black. At the present time, none of the two systems is better than the other thanks to the progress of electronics.

Treatment of the emitted wave: the demodulator

Now that the wave is modulated, it is illegible for the image processing part of the television set. It thus should be demodulated.

This stage is extremely simple: it is indeed enough to place a video or audio demodulator.

The diagram becomes: <center>

Tuner

The system seems functional with this stage, however, it is not the case. Indeed, it was specified previously that one of the interests of the modulation was to be able to emit several signals on different carrier waves in order to receive several channels. It is thus necessary to add a system able of to sort the different carrying ones.

For that it is necessary "to remove" all the waves not forming part of an interval defined by the user.

The diagram of this system is as follows:

and it is integrated in the assembly in this way:

It should be noted that a manual tuner has been just created, i.e. the user will have to choose these channels by the means of a serrated roller. Moreover, the tuner is relatively basic because it does not manage amplification.

Technology

Guiding principles

Video

Standards of diffusion

Into analogical: SECAM, STAKE, NTSC, D2MAC
Numerically: MPEG2 and MPEG4 for diffusion by satellite and TNT

Means of diffusion

Various means of diffusion can be used:

Means of reception

antennas
the quality of image TV observed in terrestrial reception Scale of Nueffer
the quality of reception numerically MPEG-2

Bibliography

Erik Barnouw, Tube of Plenty: The Evolution of American Television, Oxford University Press,
Pierre Bourdieu, On television, Reasons to act,
, The Company of the spectacle, Buchet-Chastel Editor,
Jerry Mander, Furnace Arguments for the Elimination of Television, Perennial,

Films

Not considering step taken, 1998 of the realizer Pierre Carles on the relations between the medium of French television and the French political community.

See too

National televisions

Television in France
- Chronology of French television
- History of French television
Television in Belgium
- History of television in Belgium
Television in the United States

Chains of television

Emissions of television

Others

External bonds

Gate Television - Reach the articles of Wikipédia concerning television.