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DC and is typically about 60V. The power can be introduced
at either end of the transmission line or anywhere along the
way. All that is needed is a small cord and a plug-connected
AC-powered transformer connected to the coax.
If this power is out, the good news is that AC voltage can be
used for troubleshooting the line using a standard multimeter.
Many users, especially residential, receive television
programming via a satellite dish. Large hotels and similar
facilities, often with multiple buildings some distance apart,
are also good candidates for this technology.
The troubleshooting techniques mentioned for coaxial cable
are relevant because the signal has to be conveyed to the
receiver in the building. However, installation, maintenance
and overall troubleshooting are somewhat more complex.
Satellite dishes are generally used in remote locations. They
function well, with video and audio quality equal to, or better
than, those of cable – notwithstanding occasional weather-
related outages.
The defining feature of a satellite system is the parabolic
metal antenna. A parabola is one of Euclid’s conic sections, and
BY
DAVID
HERRES
reflectors conforming to that particular curve are widely used.
Light bulb reflectors and remote listening devices are other
examples.
The dish gathers the signal contained in electromagnetic
energy coming from the satellite and focuses it at the input
end of the feedhorn, which is mounted at the dish’s focal point.
This segment of the signal path provides lots of passive
amplification, the amount determined by the diameter of the
dish. (With higher power transmission in recent years, it has
become possible to reduce the size of the dish.)
The dish must be precisely aimed so as to pick up the signal
from the satellite, which occupies a fixed position in the sky
directly over the equator. The satellite must be at a specific
altitude – 35,786km – to avoid crashing into the earth or flying
off into space. Small on-board rockets maintain the position.
There are thousands of satellites in geostationary orbit, and
additional satellites are launched as needed.
Satellites contain transponders, typically numbering 24.
Each of these is a semi-autonomous transmitter/receiver
connected to a power supply and antenna. Programming
EMONA
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