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A special kind of antenna engineered to focus on specific
broadcast source is the satellite dish. A bowl-shaped or
parabolic surface and central feed horn are the main elements of
the standard dish. For a signal to be transmitted, the dish
focuses the signal into a somewhat fine shaft of light after
which a controller sends the signal through the horn. The
receiving dish works in exactly the opposite direction of that
of the transmitter: it only receives the signal and unable to
transmit information.
The parabolic shape reflects the
radio signal inward to a particular point or the feed horn when
a beam hits the curved dish then passing the signal on the
receiving equipment. Such motion is comparable to a concave
mirror focusing light on particular point.
A satellite dish is very large- as
much as 9 to 12 meters (30 to 40 feet) in diameter. The bigger
the diameter, the more accurate is the positioning and improved
signal reception of the satellite. This dish is directed toward
the satellite where the signal will be transmitted.
Transponders- devices located on-board with which the signal is
transmitted- retransmit the satellite signal back towards the
Earth but at a different frequency.
A parabolic receiving satellite
dish then collects the quite weak signal after traveling through
space and reflects the weak signal to its focal point. The weak
signal is down-converted to a lower frequency band and amplified
by a low-noise block downconverter. The amplified signal then
travels to a satellite receiver box through coaxial cable and
the local oscillator converts the signal to the approximately
L-Band frequency range. The receiver box has a special on-board
electronics that assist in signal tuning then converting it into
a useful frequency that a standard television can make use of.
Full-size satellite dish are being
used by most television and radio channels for the transmission
of C-band satellite transmission frequencies. This provides more
viewing choice including cable with more than 250 channels
regularly transmitted and another 250 occasionally transmitted.
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