Transmission of signals from the Satellite to the Satellite DISH
In a nutshell, Satellite TV transmits video and audio signals from satellites in space to satellite dishes on the Earth’s surface. However, these satellites are geostationary satellites. These satellites are placed in a geostationary orbit and are perpetually at a constant position relative to the earth’s surface. This is achieved by orbiting at a height of 22,300 miles above the equator in the Clarke Belt. The latitude of the satellite is always zero and the longitude is constant. On every such satellite there are several transponders. A transponder is a combination of a transmitter and a receiver. Signals from the earth reach the transponder and it reflects those back on the earth’s surface.
Generally, the frequency of the received and transmitted signal is different. This frequency differentiates the signals into bands. The signals are generally on the Ku Band, Ka Band or C Band. These signals traverse these 22,300 miles and are received by the satellite dish. The satellite dish may be as large as nine feet or more or as small as 18 inches. The function of the dish is to collect the signals transmitted by the transponders and reflect them to the feed horn.
The feed horn is a component of the satellite dish system that receives the signal from the satellite dish and passes it to the Low Noise Block or Converter (LNB). This LNB is attached in or on the satellite dish. The function of the LNB is to amplify and convert a wide band of frequencies.
The signal loss which occurs in coaxial cables at high frequencies does not occur in case of LNB. Thus, the signal is amplified by the LNB and converted to a frequency that can be transmitted over a cable. This cable is called IFL or Intra-Facility Link. Often, this is a shielded coaxial cable that has BNC connectors on either side. It is a connection between the Outdoor Unit and the Indoor Unit. The signal passes from the LNB through the IFL and reaches the satellite receiver. The satellite receiver passes the signal to the TV set.
Satellite TV vendors
In the United States, DISH Network and DirecTV are the largest satellite TV vendors. Both of these are concerned with the Ku and Ka bands. The National Programming Service and Superstar are related to the C Band. If the Satellite TV is digitalized, then the satellite broadcasters can provide more television channels in the same bandwidth. Satellite TV may be in the standard resolution as well as the new ATSC High Definition format.
Journey of the signals
The data is converted to microwave signals in the Broadcast Station on the earth. The signals are transmitted from the broadcast station to the geostationary satellite. Further, the signals are then transmitted to the satellite dish. This satellite dish converts the signals to a receiver. This has broadband antenna and can collect electromagnetic energy. Depending on the type of receiver, the signal may be converted to analog, digital or High-definition frequency.
The Broadcast Station
Satellite TV is related to two major sources – the national turnaround channels like ESPN, HBO and CNN as well as local channels like ABC, CBS, NBC, PBS and Fox. The broadcast station converts all this programs into high quality and uncompressed digital stream. This stream consists of a tremendous amount of data – nearly 270 Mbps – for each channel. As this data is too large to be handled by the satellite, the broadcast station compresses it. Using MPEG-2 compression technique, the 270 Mbps is diminished to 5 to 10 Mbps. In the absence of compression, a satellite can transmit 30 channels. This number is raised to 200 channels, if compression is used. After the process of compression, the signal undergoes another process called Encryption. This is done to avoid free access by people and for security reasons.
The Satellite DISH
This encrypted signal is picked by an onboard dish on the satellite. After this signal is amplified, another dish is used to focus it back to the earth. On the surface of earth, the satellite dish has a parabolic or bowl-shaped surface. When the beam of the signal hits it, the beam is reflected inward to a specific point. Due to the parabolic shape, the satellite dish acts similar to a concave mirror. The feed horn is fitted exactly where the beam converges. When there aren’t substantial blockages between the satellite and the dish, a clear signal is received. The satellite dish is aimed directly at the satellite. In case, the satellite dish has to pick up signals from two or more satellites, then two or more feed horns are fitted on the satellite dish. Each of these feed horns relate to different satellites. The beams from the satellites get reflected from the satellite dish and converge on the different feed horns. LNB is the central component of the feed horn. The radio signals that do not carry programs are called as Noise. These are filtered and removed by the LNB and an amplified and filtered signal is passed to the satellite receiver.
The Satellite Receiver
This satellite receiver has four functions – the encrypted signal is de-scrambled, the MPEG-2 signal is converted to an analog signal (called as a NTSC format or an HDTV signal), the individual programs are extracted from the large satellite signal, a track is maintained on the pay-per-view programs and the billing information is conveyed to the computer at the provider’s headquarters. Since the receiver can extract a single program from the overall satellite signal, it is not possible to watch two different programs on two television sets connected to a single receiver. Also, it is not practical to record one program and view the other. Some receivers have in-built Digital Video Recorders. These allow pausing live television and recording it on a hard drive.
Setup of the Satellite DISH
Direct Broadcast Satellite can be availed by using a small dish that is 19 to 24 inches in circumference and installing it outside the house. The major advantage is that Satellite TV offers more number of channels as compared to cable network at very competitive prices.
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