How DTH System works

During the eighties, in India, with the launch of INSAT satellite, the TV coverage was increased by installing television receive only (TVRO) stations with low power transmitter (LPT) and high power transmitter (HPT). Here the TV programme was transmitted from Delhi through satellite and is received at various locations using antenna and receive electronics. The receive audio and video is retransmitted Terrestrial in vhf band so that normal television receiver second receive it. LPT coverage is less as the transmitter power is less while HPT coverage is wider television coverage does increased.

With the advent of satellite TV transmission, cable TV became popular in the nineties. Cable TV operators installed Antennas and receivers to receive signals from the satellite. Separate receivers are used to demodulate is TV signal. Each the modulated video and audio signal is modulated onto a separate Frequency for transfer to cable. The channel frequency and modulation plan is such that they can be received by the normal home TV receiver.

The frequencies are in VHF low, VHF high, superband, hyperband and in UHF Band. The cables are routed  to individual household and fade to the antenna circuit of the TV receiver. In the earlier days, analogue transmission was used and only one TV Channel was transmitted par transponder of the satellite. But today with digital transmission approximately almost 15 TV channels can be transmitted per transponder. Thus, from a satellite having 24 transponders, the cable operator can extract 360 channels for distribution.

Amplifiers are installed at appropriate distances along the cable route to maintain adequate signal quality. In the case of free to air channels the cable is directly connected to the antenna circuit of the TV receiver and in the case of pay channels it is connected through a set-top box. The subscriber will be authorised to receive the pay channel by the cable operator.

 Next came direct to Home (DTS) system designed to transmit TV programs directly to home receivers. The broadcaster directly connect to the user and the cable operator does not come into the picture.