Page 192 - CITS - Electronic Mechanic - TT - 2024

ELECTRONICS MECHANIC - CITS

The Components
There are five major components involved in a direct to home (DTH) or direct broadcasting (DBS) satellite system:
the programming source, the broadcast center, the satellite, the satellite dish and the receiver.
a The programming source
Satellite TV providers get programming from two major sources: International turnaround channels (such as HBO,
ESPN and CNN, STAR TV, SET, B4U etc) and various local channels (SaBe TV, Sahara TV, Doordarshan, etc).
Turnaround channels usually have a distribution center that beams their programming to a geostationary satellite.
The broadcast center uses large satellite dishes to pick up these analog and digital signals from several sources.
b The broadcast center
The broadcast center converts all of this programming into a high-quality, uncompressed digital stream. At this
point, the stream contains a vast quantity of data — about 270 megabits per second (Mbps) for each channel.
In order to transmit the signal from there, the broadcast center has to compress it. Otherwise, it would be too big
for the satellite to handle. The providers use the MPEG-2 compressed video format — the same format used to
store movies on DVDs. With MPEG-2 compression, the provider can reduce the 270-Mbps stream to about 3 or
10 Mbps (depending on the type of programming).
With digital compression, a typical satellite can transmit about 200 channels. Without digital compression, it can
transmit about 30 channels.
c Encryption & Transmission
After the video is compressed, the provider needs to encrypt it in order to keep people from accessing it for free.
Encryption scrambles the digital data in such a way that it can only be decrypted (converted back into usable
data), if the receiver has the correct decoding satellite receiver with decryption algorithm and security keys. Once
the signal is compressed and encrypted, the broadcast center beams it directly to one of its satellites. The satellite
picks up the signal, amplifies it and beams it back to Earth, where viewers can pick it up.
d The Dish
A satellite dish is just a special kind of antenna designed to focus on a specific broadcast source. The standard
dish consists of a parabolic (bowl-shaped) surface and a central feed horn. To transmit a signal, a controller
sends it through the horn, and the dish focuses the signal into a relatively narrow beam. The dish on the receiving
end can’t transmit information; it can only receive it. The receiving dish works in the exact opposite way of
the transmitter. When a beam hits the curved dish, the parabola shape reflects the radio signal inward onto a
particular point, just like a concave mirror focuses light onto a particular pointThe curved dish focuses incoming
radio waves onto the feed horn.
e The Receiver
The end component in the entire satellite TV system is the receiver. The receiver has four essential jobs: It de-
scrambles the encrypted signal. In order to unlock the signal, the receiver needs the proper decoder chip for that
programming package. It takes the digital MPEG-2 signal and converts it into an analog format that a standard
television can recognize.
Some receivers have a number of other features as well. They pick up a programming schedule signal from the

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CITS : E & H - Electronics Mechanic - Lesson 108 - 117