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Satellite TV Technology Description for the Non-Expert
Satellites used for television signals are in geostationary orbit 22,300 miles above the earth's
equator.
Echostar, the parent company of Dish Network, owns the majority of the Satellite TV apparatus
currently serving subscribers in the US, Canada, Puerto Rico, and Hawaii. DirecTV also owns a
fleet of satellites which transmit the current channel lineup for the same geographic areas as
Dish Network. In fact, because of its dramatic recent growth, Direct TV actually leases
transponder space in the Echostar 110and 119 satellites.
 Satellite television, like other communications relayed by satellite, starts
with a transmitting antenna located at an uplink facility. Uplink satellite dishes are very
large, as much as 9 to 12 meters (30 to 40 feet) in diameter. The increased diameter results
in more accurate aiming and increased transmission signal strength to the satellite. The
uplink dish is pointed toward a specific satellite and the uplinked signals are transmitted
within a specific frequency range, so as to be received by one of the transponders tuned to
that frequency range aboard that satellite. The transponder 'retransmits' the signals back to
Earth but at a different frequency band. A process known as 'translation', used to avoid
interference with the uplink signal. The leg of the signal path from the satellite to the
receiving Earth station is called the downlink.
A typical satellite carries up to 32 transponders for Ku-band satellites, and up to 24
transponders for a C-band only satellites. Typical transponders each have a bandwidth
between 27 MHz and 50 MHz. Each geo-stationary C-band satellite needs to be spaced 2 degrees
from the next satellite (to avoid interference). C-band transmission is susceptible to
terrestrial interference, while Ku-band transmission is affected by rain, since
water is an excellent absorber of microwaves at this particular frequency.
The downlinked satellite signal, which is quite weak after traveling more than 22,300 miles,
is collected by a typically small parabolic receiving dish,
 which reflects
the weak signal to the dish's focal point (a point in space in front of the dish, where the
reflected signal is concentrated). Mounted at the end of a bracket at the dish's focal point
is a device called a size=2> low-noise block downconverter (LNB).
 The LNB amplifies
the relatively weak signals, filters the block of frequencies in which the satellite TV signals
are transmitted, and converts the block of frequencies to a lower frequency range that can be
'piped' into low impedance cable.
The advantage of using an LNB are that cheaper cable could be used to connect and route the
signal to an indoor satellite receiver. The shift to less expensive cheaper 75 Ohm technology
allows for use of digital transmission of signals, instead of the more expensive, and clunky,
analog signals.
Direct broadcast satellite dishes today are mostly fitted with one or more LNBF's.
An LNBF is just a feedhorn integrated into the LNB. This is the technology currently used by
all the satellite services providers. Hughes Satellite uses and additional low power transmitter
element on their Hughesnet Satellite Internet product. This technology will be described at a
later point in this web page.
 The satellite receiver
demodulates and converts the signals to the desired form (outputs for television, audio, data,
etc..). Almost all the time, the receiver includes the capability to unscramble or decrypt the
incoming signal, which is usually scrambled at the uplink. This is what both DirecTV and Dish
Network include in their programmable receiver lineup, in order to protect their investments,
and to ensure that few, if any, pirate their signals for private use, or profit. This type of
receiver is called an Integrated Receiver/Decoder (IRD).
The FTA (Free To Air) technology (based on the MPEG-2 video standard), is mostly unscrambled,
but it too is slowly converting over to using scrambled trasmit of signals. It makes sense that
satellite tv providers charge for their services, considering the costs involved in launching
one of these satellites up more than 22,000 miles, and the ground resources needed to use build
and maintain all these systems.
The cable connecting the receiver to the LNBF or LNB must be of the low loss type RG-6, quad
shield RG-6 or RG-11, etc. It cannot be standard RG-59 due to the cable impedance capabilities
insofar as its digital data portability, or lack thereof.
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Copyright 2009 MeridianSatelliteTV.com Colorado Springs, Colorado All Rights
Reserved
Dishnetwork is a trademark of EchoStar Communications Corporation.
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