 |
 |
|
|
|
|
What is Satellite TV ?
Satellite television can be defined
as a television system in which a signal is sent to a satellite
situated almost 37,000 km away from the Earth’s surface; this
satellite after the receiving the signal, amplifies it and then
transmits it back to the Earth. All these satellites are placed
in such a way that they appear to be fixed in one position
relative to that of the Earth. This is known as geosynchronous
orbit. Each of the satellite is sent out to space with a speed
of about 7,000 mph. With this speed, they attain a distance of
almost 22,200 miles above the Earth’s surface. The objective is
that after reaching this distance, it starts orbiting the earth,
and completing it once in every 24 hours- the same time that the
earth takes in completing one rotation. Since the satellite
moves at the same pace as that of the Earth, it can pick up the
transmitted signal without much difficulty.
Thus the satellite theory is: if a signal is sent out to space
at the right speed and on the right path, it stays there
orbiting the Earth for many years. It was the in the year 1962,
that the first TV signal was relayed-from Europe to the Telstar
satellite over North America. The average life span of this
satellite does not exceed more than 10 years. It must be noted
that even though the satellite revolves round the Earth at the
same speed, its orbit becomes unmanageable if not monitored
regularly. Thus the satellites have small rockets which are
responsible for the adjustment of their positions. However,
their fuel gets exhausted after about 10 years and the satellite
starts showing signs of wearing out by “wobbling up and down” in
the orbital plane. A new satellite is then launched and the old
one is sent off to a “higher parking orbit”.
|
|
|
|
|
|
|
|
|
|
In the year 1969, with the launch of
Intelsat 3 satellites, there was a spurn in the worldwide
television and speech communications network and it spread all
across the Atlantic, Pacific and Indian Ocean. Today though
there are quite a few satellites that are completely dedicated
to television broadcasting, most perform multifunctional tasking
like video conferencing, international voice and data
communications, and even data broadcasting for the retail
industry. A large number of companies are also seeking the help
of satellites for accessing broadband internet by the means of
spot beams.
When Satellite TV entered the consumer market, the home dishes
that were available were not only expensive but also had a
clumsy look - a huge metal unit occupying a big place in the
backyard. Thus it was not widespread and was only found in the
homes of the “die-hard” fans that were willing to go through all
the pains of having a dish TV at home. |
|
These early satellite TV viewers
experimented a lot with their instruments. They tried to
discover the programs that were not accessible to the mass
audience. The dish and receiver gave them the opportunity to
select from a wide range of programs – from various foreign
stations to the NASA actions and a lot more. Till date there are
customers who prefer to choose their own programs in this method
but most of the users prefer to select from a DBS or a direct
broadcast satellite (more commonly known as Direct-to-Home)
provider like the DirecTV or the Dish Network. The provider
chooses a set of programs and then broadcasts them to
subscribers as a set package. In fact his intention is to
provide as many channels as possible to compete against the much
popular, Cable TV.
The present day Satellite TV
transmission is completely digital which means a much superior
and picture quality as compared to the earlier programming. The
earlier satellite television transmitted programming in the
C-band radio -- radio in the 3.4-gigahertz (GHz) to 7-GHz
frequency range. The present digital broadcast transmits
programming in the Ku frequency range (12 GHz to 14 GHz)!
DBS is a relatively new discovery in the field of Television
network. The DBS equipments are also known as the “mini dish”
systems.
The key mechanisms involved in the direct to home (DTH)
satellite system are: the programming source, the broadcast
center, the satellite, the satellite dish and the receiver.
Programming sources are the channels that provide programming
for broadcast. The DBH providers pay the companies and broadcast
their shows (for e.g. HBO, ESPN). Thus he acts as a negotiator
between the viewer and the programming sources. The cable
providers use the same principle.
The broadcast center can be defined as the nucleus of the
system. All the signals received at this centre are transmitted
to the satellite in the geostationary orbit. The satellites
receive these signals and after amplification send them back to
the Earth. These signals are then collected by the viewer's dish
from the satellite and sent to the receiver. The receiver
processes these signals and then transmits them to the
television for viewing.
|
|
The providers receive their programs
from the national turnaround channels (such as HBO, ESPN and
CNN) and the local channels. The turnaround channels also
provide programs for cable the television, and the local
channels broadcast their programs over the airwaves. The
turnaround channels have a distribution centre that transmits
the programs to a geostationary satellite. The broadcast centre
takes the help of these satellites to receive the digital
signals from the various sources. The local stations on the
other hand do not transmit their programming to satellites.
Hence in order to include local programs the provider needs to
install a small local communication equipment. This equipment
receives the local signals through the antenna or a fiber optic
cable and then relays them to the broadcast centre for
transmission.
|
|
|
|
The broadcast center, after
receiving all these programs, converts them into a high-quality,
uncompressed digital stream. The stream contains a vast amount
of data-- about 270 megabits per second (Mbps) for each channel.
This is too big for the satellite and hence needs to be
compressed. Thus the high-quality digital stream of video goes
through an MPEG-2 encoder, which converts the programming to
MPEG-2 video of the correct size and format for the satellite
receiver in the consumers’ house.
It is to be noted that with the help of MPEG-2 compression, a
270-Mbps stream can be reduced to about 5 or 10 Mbps (depending
on the type of programming). This is one of the most important
things that have made DBS service a great success. Without
digital compression, a satellite can transmit about 30 channels
whereas with the compression about 200 channels! The common
parabolic shaped satellite dish is actually a special kind of
antenna that is designed to focus on a particular transmission
source. The dish also consists of a central feed horn. To
transmit a signal, a controller first sends it through the feed
horn, and the dish converts it into a narrow beam. The dish is a
receiver and cannot transmit signals. It operates exactly
opposite to the transmitter. When a signal hits the curved dish,
the parabola shape reflects it inward onto to the central feed
horn which in turn transmits the signal to the receiving
equipment. The low noise block-down converter, or LNB is the key
element in the feed horn. The LNB amplifies the radio signal
that is reflected by the dish and filters out the noise. It then
passes this amplified, filtered signal to the satellite receiver
inside the viewer's house.
|
|
Article Contributed By: Sukanaya
Banerjee
|
|
|
|
|
