Contents
TELEVISION SIGNAL BROADCASTING IN SATELLITE
by
SHANTANU RAJWADE
SHANTANU REGE
DEEPAK RAMINEEDI
Introduction:
Traditional forms of communication i.e. using cables, require physical connectivity of the transmitter and receiver. Besides, this is also hindered due to geographical limitations. eg. Having a trans-Atlantic cable to connect the North America and Europe would be economically and physically unviable. Similarly, communication with ships at sea, aeroplanes or for that matter any moving object, would pose a problem for this form of communication. All these problems are easily overcome if we make optimal use of natural resource that is freely available to us – SPACE.Using Geo-stationary satellites which orbit 35,700 kilometres above the earth’s surface give us the freedom to communicate without above limitations and also has the unique advantage that the cost of communication is independent of distance. Today they are used in a wide variety of applications ranging from television broadcasting, mobile telephony, radiometry and weather forecasting.
In our future discussion we focus our attention on use of satellites in television broadcasting.
BASIC EARTH STATION - SATELLITE LINK MODEL
Broadcasters uplink scrambled or encrypted signals(audio and video) to a satellite at a particular frequency. The signals are encrypted to prevent their unauthorized reception before retransmission.The signal received by the satellite is rather weak. Therefore, it is first amplified by the receiver antenna, filtered and further amplified by a low noise Tunnel Diode Amplifier (TDA). The output of the satellite is the frequency displaced and processed version of the input. This frequency translator is required to prevent interference from the high power satellite input to the output. All the tasks mentioned above can be thought of as being performed by a single device within the satellite namely, the TRANSPONDER.
After traveling 22,000 miles to a ground-based antenna, the signals are again very weak and must be amplified. Therefore, satellite “dishes” focus the signals onto the actual antenna. The signals from the antenna are then fed to a “low-noise block,” or LNB, amplifier which amplifies signal and converts them to a lower frequency. The lower the power of the satellite, the larger the antenna required to focus the signals. A C-Band satellite, with power ranging between 10 and 17 watts per transponder, typically has an antenna between 5 and 10 feet in diameter; whereas a highpowered Ku-Band satellite, with a range of 100 to 200 watts per transponder, only requires an antenna 18 inches in diameter. The downlink path of the signal comprises of a receiving station, and a network of descramblers\decoders.
Each integrated receiverdecoder (IRD) is assigned a unique address code. The authorization center uses this code to turn individual decoders on or off and even selectively control large groups of decoders, thus enabling them to receive the signal.
