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Knowledge Is Key
For Intelligent Decisions
Satellite Logic is a leading,
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To receive high quality satellite TV you need to be connected to one of
the main satellite TV providers and of course a good TV set. But let's
have a look at the technical process of the satellite TV reception.
At the broadcast center, the high-quality digital stream of video goes
through an MPEG encoder, which converts the programming to MPEG-4
video of the correct size and format for the satellite receiver in your
house. Encoding works in conjunction with compression to analyze each
video frame and eliminate redundant or irrelevant data and extrapolate
information from other frames. This process reduces the overall size of
the file.
This process occasionally produces artifacts, which are glitches in the
video image. One artifact is macroblocking, in which the fluid picture
temporarily dissolves into blocks. Macroblocking is often mistakenly called
pixilating, a technically incorrect term which has been accepted as slang
for this annoying artifact. Graphic artists and video editors use "pixilating"
more accurately to refer to the distortion of an image. There really are
pixels on your TV screen, but they're too small for your human eye to
perceive them individually, they're tiny squares of video data that make
up the image you see.
The rate of compression depends on the nature of the programming. If
the encoder is converting a newscast, it can use a lot more predicted
frames because most of the scene stays the same from one frame to the
next. In more fast-paced programming, things change very quickly from
one frame to the next, so the encoder has to create more intraframes.
As a result, a newscast generally compresses to a smaller size than
something like a car race.
After the video is compressed, the provider encrypts it 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 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 with an
onboard dish, amplifies the signal and uses another dish to beam the
signal back to Earth, where viewers can pick it up.
When the signal reaches the viewer's house, it is captured by the
satellite 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 curved satellite dish reflects energy from the feed horn, generating
a 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 point. In an ideal setup,
there aren't any major obstacles between the satellite and the dish, so
the dish receives a clear signal.
In some systems, the dish needs to pick up signals from two or more
satellites at the same time. The satellites may be close enough together
that a regular dish with a single horn can pick up signals from both. This
compromises quality somewhat, because the dish isn't aimed directly at
one or more of the satellites. A new dish design uses two or more horns
to pick up different satellite signals. As the beams from different
satellites hit the curved dish, they reflect at different angles so that one
beam hits one of the horns and another beam hits a different horn.
The central element in the feed horn is the low noise blockdown
converter, or LNB. The LNB amplifies the radio signal bouncing off the
dish and filters out the noise (radio signals not carrying programming).
The LNB passes the amplified, filtered signal to the satellite receiver
inside the viewer's house.
The end component in the entire satellite TV reception 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.
The provider can communicate with the chip, via the satellite signal, to
make necessary adjustments to its decoding programs. The provider
may occasionally send signals that disrupt illegal de-scramblers as an
electronic counter measure (ECM) against illegal users.
* It takes the digital MPEG-2 or MPEG-4 signal and converts it into an
analog format that a standard television can recognize. In the United
States, receivers convert the digital signal to the analog National
Television Systems Committee (NTSC) format. Some dish and receiver
setups can also output an HDTV signal.
* It extracts the individual channels from the larger satellite signal. When
you change the channel on the receiver, it sends just the signal for that
channel to your TV. Since the receiver spits out only one channel at a
time, you can't tape one program and watch another. You also can't
watch two different programs on two TVs hooked up to the same
receiver. In order to do these things, which are standard on
conventional cable, you need to buy an additional receiver.
* It keeps track of pay-per-view programs and periodically phones a
computer at the provider's headquarters to communicate billing
information.
Receivers have a number of other features as well. They pick up a
programming schedule signal from the provider and present this
information in an onscreen programming guide.
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