GROSS STRUCTURE

• The frame adopted in all television systems is rectangular with width/height ratio, i.e., aspect  ratio = 4/3. There are many reasons for this choice.
•  In human affairs most of the motion occurs in the horizontal plane and so a larger width is desirable.
•  The eyes can view with more ease and comfort when the width of a picture is more than its height.
•  The usage of rectangular frame in motion pictures with a width/height ratio of 4/3 is another important reason for adopting this shape and aspect ratio. 
• This enables direct television transmission of film programmes without wastage of any film area                     .
• It is not necessary that the size of the picture produced on the receiver screen be same as that being televised but it is essential that the aspect ratio of the two be same, otherwise the scene details would look too thin or too wide.
•  This is achieved by setting the magnitudes of the current in the deflection coils to correct values, both at the TV camera and receiving picture tube.
•  Another important requirement is that the same coordinates should be scanned at any instant both by the camera tube beam and the picture tube beam in the receiver.
•  Synchronizing pulses are transmitted along with the picture information to achieve exact congruence between transmitter and receiver scanning systems.