A brief History of Television

Television 

Television much of our future depends on the way we use this medium of communication for its influence on thinking and action is tremendous suppose we were privileged to enter the inner sanctum of a television station here in the control room.

How is all this done what causes this the almost instantaneous transmission of sight and sound, it is an electron beam that paints the picture on your receiver tube, you can see the mark of this beam when you turn your receiver off let's look at one of these receiver tubes.

The men who at the touch of a button control the picture going to our homes where we at the touch of a button select from a variety of programs news stories entertainment-education sports and advertising for in a few short years television has become one of the greatest merchandising media.

Find out how television works this is known as a cathode ray tube because under high voltage electricity the cathode gives off a beam or ray of electrons, you might call this an electron gun.

Which shoots a stream of tiny negative particles at the face of the fuel, the fluorescent coating on the face glows where the electron beam strikes it now.

Let's look into a tv camera through one of its lenses, an image is formed not on film but on another tube a tube which costs more than a thousand dollars this type is called the image orthicon.

Tool in it is another electron gun that sends out a steady stream of electrons now this target is made to pick up a series of electrical charges when the lens forms an image on the sensitive plate and these charges vary the magnitude of the returning electron beam to understand this let's imagine that.

We want to televise a single dot, not a white dot not a black dot but something in between in the camera tube the lens forms an image of the dot on the plate set up a charge on the target.

According to the brightness of the image, the electron beam is changed when it returns from the target this the changed beam is amplified and sent out by the fuel in the television transmitter this picture signal is amplified.

Combined with a very high-frequency the carrier wave with the fluctuation caused by the image of the grey dot goes to the transmitter antenna and is radiated from the top of the tower the receiver the antenna picks up the wave and sends it down the lead-in wires to the receiver here the signal control the electron beam so that it strikes.

The fluorescent face is just hard enough to make a gray dot on the receiver of the screen thus the basis of television is an image of life.

Which controls electricity which regulates transmitter waves which again control electricity and finally is turned back into the light but television is more than a great art it's a whole picture and it moves to understand.

How television makes pictures that move think of this when you read a book you don't read the whole page at once you read a little bit at a time swinging your eye across the line after line in the tv camera tube the beam of electrons.

                         

Can do much the same electrons are affected by magnetic fields of deflecting coils these coils make the electron beam sweep back and forth across the target, these coils make the beam swing up and down together they swing the beam across one line then back to cross another lower down.

Still another lower thus in effect the beam looks at each point of the picture and it varies according to the brightness of each point the movement of the beam in the camera is accurately timed in the tv transmitter by a sync generator.

which generates synchronizing pulses these pulses are also sent out over the air as part of the video signal in your receiver these pulses synchronize the sweep of the electron beam to the station being received.

As the beam sweeps back and forth line after line the strength of the beam keeps changing modulated by the video signal where the beam is strong the tube glows brightly.

Where it's weak the tube remains dark thus the camera and the receivers watching it is electronically linked together and the signal from each point in the camera.

 The tube is transmitted and turned into a picture of the same point on the receiver tube so on your receiver tube pictures are painted by an invisible beam darting back and forth at speeds thousands of miles per hour in the most common forms of television.

The beam scans every other line then goes back to fill in this is called interlaced scanning with 60 interlaced pictures per second or 30 full pictures per second it assures a steady image with no flicker and because your eye has a persistence of vision this series of pictures gives the illusion of motion.

 Add sound through FM radio and you have a television in today's airwaves television occupies the very high and ultra-high frequencies these waves cannot normally be received beyond the horizon.

So the area of tv reception is limited television transmitters are linked sometimes by coaxial cable a special wiring tube arrangement to carry tv signals and sometimes by relay stations located usually.

On high ground, they receive a signal through one of the horn-shaped antennas boosted stronger and transmitted on to the next station thus television is sent from coast to coast images picked up by cameras and turned into radio wave signals which tell a fleeting invisible beam.

Pictures in your home wouldn't you like to know more about television the cameras the lights the production techniques for those who understand television, there are many vocational opportunities let this is only the beginning of your study of television.

The End