Satellites:
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| First off,
A
free-to-air or FTA Receiver is a satellite TV receiver
designed solely to receive unencrypted broadcasts.
Modern decoders are typically compliant with the
MPEG-2/DVB-S standard for digital television, while
older FTA receivers relied on analog satellite
transmissions which have declined rapidly in recent
years. Overwhelmingly, FTA receivers are manufactured
in South Korea and China.
A few high-end receivers feature HDTV. These
usually include an ATSC over-the-air digital
television tuner and MPEG-4 support. A few HDTV units
allow for the addition of a UHF remote control.
However, an 8PSK module can be installed in place of
the UHF remote and allows the receiver to decode the
format used on most Dish Network high definition
programming.
There are different types of dishes you can use.
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Individual dishes serving one dwelling: Direct to
Home (DTH).
Collective dishes, shared by several dwellings:
satellite master antenna television (SMATV) or
communal antenna broadcast distribution (CABD).
VSATs
Automatic Tracking Satellite Dish
A satellite dish is a type of parabolic antenna
designed with the specific purpose of transmitting
signals to and/or receiving from satellites. A
satellite dish is a particular type of microwave
antenna. Satellite dishes come in varying sizes and
designs, and are most commonly used to receive
satellite television. Many of the offset type of
satellite dishes are sections of a larger parabolic
dish.
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Modern dishes intended for home
television use are generally 43 cm (18 in) to 80 cm (31 in) in
diameter, and are fixed in one position, for Ku-band reception
from one orbital position. Prior to the existence of direct
broadcast satellite services, home users would generally have
a motorised C-band satellite dish of up to 3 metres in
diameter for reception of channels from different satellites.
Overly small dishes can still cause problems, however,
including rain fade and interference from adjacent satellites.
In a single receiver residential installation there is
a single cable from receiver to LNB and the receiver uses
different power supply voltages (14/18V) to select
polarization and pilot tones (22 kHz) to instruct the LNB to
select one of the two frequency bands. In larger installations
each band and polarization is given its own cable, so there
are 4 cables from the LNB to a switching matrix, which allows
the connection of multiple receivers in a star topology using
the same signalling method as in a single receiver
installation.
The theoretical gain (directive gain) of a dish
increases as the frequency increases. The actual gain depends
on many factors including surface finish, accuracy of shape,
feedhorn matching.
With lower frequencies, C-band for example, dish
designers have a wider choice of materials. The large size of
dish required for lower frequencies led to the dishes being
constructed from metal mesh on a metal framework. At higher
frequencies, mesh type designs are rarer though some designs
have used a solid dish with perforations.
The dish is a reflector antenna and almost anything
that reflects radio frequencies can be used as a reflector
antenna. This has led to dustbin lids, woks and other items
being used as "dishes". Coupled with low noise LNBs and the
higher transmission power of DTH satellites, it is easier to
get a usable signal on some of these "dishes".
Another common satellite dish is the VSAT. This
provides two way satellite internet communications for both
consumers and private networks for organisations. Today most
VSATs operate in Ku band, C band is restricted to less
populated regions of the world. There is a move which started
in 2005 towards new Ka band satellites operating at higher
frequencies, offering greater performance at lower cost. These
antennas vary from 74cm to 120cm in most applications though
C-band VSATs may be as large as 2.4m.
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