27-09-2012, 11:36 AM
DOORDARSHAN KENDRA , DELHI
DOORDARSHAN.doc (Size: 2.38 MB / Downloads: 82)
ABOUT DOORDARSHAN KENDRA
Doordarshan is the public television broadcaster of India and a division of Prasar Bharti, and nominated by the Government of India. It is one of the largest broadcasting organizations in the world in terms of the infrastructure of studios and transmitters.
Doordarshan Kendra is a milestone in the field of entertainment and education media source.
DDK, Delhi has the Largest Programmes recording Studio in the Asia. They Broadcast 30 channels in 22 languages over the country.
AIR and Doordarshan aims to provide information, education and entertainment for the public. Its network of 1400 terrestrial transmitters cover more than 90.7% of India's population.
INTRODUCTION
An earth station, ground station, or earth terminal is a terrestrial terminal station designed for extraplanetary telecommunication with spacecraft, and/or reception of radio waves from an astronomical radio source. Earth stations are located either on the surface of the Earth, or within Earth's atmosphere. Earth stations communicate with spacecraft by transmitting and receiving radio waves in the super high frequency or extremely high frequency bands (e.g., microwaves). When an earth station successfully transmits radio waves to a spacecraft (or vice versa), it establishes a telecommunications link.
When a satellite is within an earth station's line of sight, the earth station is said to have a view of the satellite. It is possible for a satellite to communicate with more than one earth station at a time. A pair of earth stations are said to have a satellite in mutual view when the stations share simultaneous, unobstructed, line-of-sight contact with the satellite.
Video Signal Generation
Video is nothing but a sequence of pictures. The image we see is maintained in our eye for 1/16sec. So if we see images at the rate more than 16 pictures/sec, our eyes cannot recognize the difference and we see the continuous motion. In movies camera and movie projector it is found that 24 fps is better for human eyes. TV system could also use this rate but in PAL system 25fpm is selected. In TV cameras image is converted in electrical signal using photosensitive material. Whole image is divided into many micro particles known as pixels. These pixels are small enough so that our eyes cannot recognize pixels and we see continuous image.
Thus, at any particular instance there are almost infinite numbers of pixels that need to be converted in electrical signal simultaneously for transmitting picture details. However this is not possible practical because it is no feasible to provide a separate path for each pixel. In practice this problem is solved by method known as Scanning in which information is converted one by one pixel, line by line and frame by frame.
VIDEO CHAIN
The video we see at our home is either pre-recorded in studio or live telecasted. Block diagram shown in fig illustrates different chains of video recording, video playback, news, and live broadcasting. In First chain we will understand studio program recording. Camera output from the studio hall is sent to CCU where many parameters of video signals are controlled. Output signal of CCU after making all corrections is sent to VM in PCR-1 (production control room). Output of 3 to 4 cameras comes here and final signal is selected here using VM according to a director’s choice.