satellite television first hit the market, home dishes were
expensive metal units that took up a huge chunk of yard space.
In these early years, only the most die-hard TV fans would
go through all the hassle and expense of putting in their own
dish. Satellite TV was a lot more difficult than broadcast and
Today, you see compact satellite dishes perched on rooftops
all over the United States. Drive through rural areas beyond
the reach of the cable companies and you'll find dishes on
just about every house. The major satellite television
companies are bringing in more customers every day with the
lure of movies, sporting events and news from around the
In this edition of HowStuffWorks,
we'll find out what satellite television is all about, from TV
station to TV set.
What is Satellite TV?
satellite television is a lot like broadcast television. It's
a wireless system for delivering television programming
directly to a viewer's house. Both broadcast television and
satellite stations transmit programming via a radio signal
Radio Works for information about radio broadcasting).
Broadcast stations use a powerful antenna to transmit radio
waves to the surrounding area. Viewers can pick up the signal
with a much smaller antenna. The main limitation of broadcast
television is range. The radio signals used to broadcast
television shoot out from the broadcast antenna in a straight
line. In order to receive these signals, you have to be in the
direct "line of sight" of the antenna. Small obstacles
like trees or small buildings aren't a problem; but a big
obstacle, such as the Earth, will reflect these radio waves.
If the Earth were perfectly flat, you could pick up
broadcast television thousands of miles from the source. But
because the planet is curved, it eventually breaks the
signal's line of site. The other problem with broadcast
television is that the signal is often distorted even
in the viewing area. To get a perfectly clear signal like you
find on cable, you have to be pretty close to the broadcast
antenna without too many obstacles in the way.
Satellite television solves both of these problems by
transmitting broadcast signals from satellites
orbiting the Earth. Since satellites are high in the sky,
there are a lot more customers in the line of site. Satellite
television systems transmit and receive radio signals using
specialized antennas called satellite dishes.
Satellites are higher in the sky than TV
antennas, so they have a much larger "line of sight"
The television satellites are all in geosynchronous
orbit, meaning that they stay in one place in the sky
relative to the Earth. Each satellite is launched into space
at about 7,000 mph (11,000 kph), reaching approximately 22,200
miles (35,700 km) above the Earth. At this speed and altitude,
the satellite will revolve around the planet once every 24
hours -- the same period of time it takes the Earth to make
one full rotation. In other words, the satellite keeps pace
with our moving planet exactly. This way, you only have to
direct the dish at the satellite once, and from then on it
picks up the signal without adjustment, at least when
everything works right. (See How
Satellites Work for more information on satellite orbits.)
At the core, this is all there is to satellite television.
But as we'll see in the next section, there are several
important steps between the original programming source and
The Overall System
Early satellite TV
viewers were explorers of sorts. They used their expensive
dishes to discover unique programming that wasn't necessarily
intended for mass audiences. The dish and receiving equipment
gave viewers the tools to pick up foreign stations, live feeds
between different broadcast stations, NASA activities and a
lot of other stuff transmitted using satellites.
Some satellite owners still seek out this sort of
programming on their own, but today, most satellite TV
customers get their programming through a direct broadcast
satellite (DBS) provider, such as DirecTV or the Dish
Network. The provider selects programs and broadcasts them to
subscribers as a set package. Basically, the provider's goal
is to bring dozens or even hundreds of channels to your
television in a form that approximates the competition, cable
TV. Unlike earlier programming, the provider's broadcast is
completely digital, which means it has much better
picture and sound quality (see How Digital
Television Works for details). Early satellite television
was broadcast in C-band radio -- radio in the
3.4-gigahertz (GHz) to 7-GHz frequency range. Digital
broadcast satellite transmits programming in the Ku
frequency range (12 GHz to 14 GHz ).
There are five major components involved in a direct to
home (DTH) satellite system: the programming source, the
broadcast center, the satellite, the satellite dish and the
- Programming sources are simply the channels that
provide programming for broadcast. The provider doesn't
create original programming itself; it pays other companies
(HBO, for example, or ESPN) for the right to broadcast their
content via satellite. In this way, the provider is kind of
like a broker between you and the actual programming
sources. (Cable television companies work on the same
- The broadcast center is the central hub of the
system. At the broadcast center, the television provider
receives signals from various programming sources and beams
a broadcast signal to satellites in geostationary orbit.
- The satellites receive the signals from the
broadcast station and rebroadcast them to the ground.
- The viewer's dish picks up the signal from the
satellite (or multiple satellites in the same part of the
sky) and passes it on to the receiver in the viewer's house.
- The receiver processes the signal and passes it
on to a standard television.
In the next few sections, we'll look at each step in the
process in greater detail.
Satellite TV providers get
programming from two major sources: national turnaround
channels (such as HBO, ESPN and CNN) and various local
channels (the NBC, CBS, ABC, PBS and Fox affiliates in a
particular area). Most of the turnaround channels also provide
programming for cable television, and the local channels
typically broadcast their programming over the airwaves.
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.
Most local stations don't transmit their programming to
satellites, so the provider has to get it another way. If the
provider includes local programming in a particular area, it
will have a small local facility consisting of a few racks of
communications equipment. The equipment receives local signals
directly from the broadcaster through fiber-optic
cable or an antenna and then transmits them to the central
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. In the next section, we'll find out how
the signal is compressed.
Compression, Encryption, Transmission
two major providers in the United States 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 5 or 10 Mbps (depending on the type of
programming). This is the crucial step that has made DBS
service a success. With digital compression, a typical
satellite can transmit about 200 channels. Without digital
compression, it can transmit about 30 channels.
At the broadcast center, 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 your house.
The MPEG encoder analyzes each frame and decides how to
encode it. The encoder eliminates redundant or irrelevant
data, and extrapolates information from other frames to reduce
the overall size of the file. Each frame can be encoded in one
of three ways:
- As an intraframe - An intraframe contains the
complete image data for that frame. This method of encoding
provides the least compression.
- As a predicted frame - A predicted frame contains
just enough information to tell the satellite receiver how
to display the frame based on the most recently displayed
intraframe or predicted frame. This means that the frame
contains only the data that relates to how the picture has
changed from the previous frame.
- As a bidirectional frame - To display a
bidirectional frame, the receiver must have the information
from the surrounding intraframe or predicted frames. Using
data from the closest surrounding frames, the receiver
interpolates the position and color of each pixel.
This process occasionally produces "artifacts" --
little glitches in the video image -- but for the most part,
it creates a clear, vivid picture.
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 other sorts of
programming, such as action movies and music videos, things
change very quickly from one frame to the next, so the encoder
has to create more intraframes. As a result, something like a
newscast generally compresses to a much smaller size than
something like an action movie.
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 decryption algorithm and security
keys. (See How
Encryption Works for more information.)
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 a another dish to beam the signal back to
Earth, where viewers can pick it up.
In the next section, we'll see what happens when the signal
reaches a viewer's house.
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 dish reflects energy from the feed
horn, generating a narrow
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
The curved dish focuses incoming radio waves
onto the feed
In this case, the point is the dish's feed horn, which
passes the signal onto the receiving equipment. 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 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. 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 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 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
- 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.
Many receivers have parental lock-out options, and some have
built-in digital video
recorders (DVRs), which let you pause live television or
record it on a hard
While digital broadcast satellite service is still lacking
some of the basic features of conventional cable (the ability
to easily split signals between different TVs and VCRs, for
example), its high-quality picture, varied programming
selection and extended service areas make it a good
alternative for some. With the rise of digital cable,
which also has improved picture quality and extended channel
selection, the TV war is really heating up. Just about
anything could happen in the next 10 years as all of these
television providers battle it out.
For much more information on satellite television and other
broadcast systems, check out the links on the next page.
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