23-11-2012, 01:02 PM
Television Broadcasting In Doordarshan
Television Broadcasting.ppt (Size: 4.22 MB / Downloads: 74)
Introduction
Doordarshan is one of the largest organizations in the world
It makes available television over 87% of population
Came into existence on Sept. 15, 1959
In visakhapatnam, TV transmissions got started in 1984 with 100w BEL transmitter operating on VHF band ,channel-7
In 2004, another transmitter called NEC was introduced for DD news services
Which type of antenna is used and why?
An Antenna is metallic device which radiate and receive radio waves…
Basic Properties that an antenna should possess…
Various types of antennas…
The antenna being used in Doordarshan Kendhra-HPT
Benefits of using Parabolic antenna…
Parabola Dish antenna as a Reflector
Geometry of a Parabolic dish antenna
As a reflector for reception and transmission
Exhibits very high gain and sharp directivity
Satellite Communications
Satellite communications are comprised of 2 main components
They are of a Space segment and an earth segment
Satellite is a space segment which composes of 3 separate units called fuel system, controls and a transponder
In communications, satellite is used as a repeater
VSB Modulator
It generates the amplitude modulated vision IF signal at 38.9MHz
Video signal is fed to boot strap buffer circuit where the signal is inverted and then fed to darlington pair
And further the video signal is clamped
The balanced modulator has both clamped video signal and IF carrier
The modulator output is filtered and amplified by the IF amplifier
IF synthesizer is tuned to 38.9MHz