CABLE TELEVISION (CABLE TV):
Cable television is a type of CCTV in which users
get regular channel television signals over coaxial cables in exchange for a
monthly fee. Master Antenna TV (MATV) is needed, when a common
antennal system is utilized to transmit a strong signal to every TV set
connected to the system through coaxial cable.
The cable television system is used to broadcast
high-quality television signals to a large number of people. Subscribers that
pay a charge for this service get access to more TV programming through this
arrangement. The cable system might have more active channels (VHF
and UHF) than a receiver can directly select. This necessitates the
employment of a unique active converter in the head end.
Cable TV's primary signal source is a constellation of satellites. Satellite transmissions are received using high power parabolic dish antennas. Most communication satellite downlink communications are in the C-band (3700-4200 MHz) frequency range.
Figure:
The block diagram of a cable television system
The block diagram of cable television is shown
above. Dish antenna signals are first transformed into a lower frequency using
a Low Noise Block Converter (LNBC). Conventional antennas erected on high-rise
buildings receive VHF and UHF terrestrial broadcast transmissions. Local sports
and cultural programming might be broadcast through the cable TV network. Cable
network also distributes programmes such as popular movies and music that have
been already recorded.
The combining network applies signals from numerous
TV stations. The LNB converter converts the signal received by the dish antenna
into low frequency signals. Similarly, a translator converts the signal
received by a UHF antenna into low-frequency impulses. The combining network
combines all of the signals and allocates each channel to a different carrier
frequency.
Through a broadband distribution amplifier, the
outputs of the combining network are routed to a number of trunk lines. The
purpose of a distribution amplifier is to boost the signal amplitude to a
higher level in order to compensate for distribution system losses. Through
co-axial trunk lines, the distribution amplifier's output is sent to the
splitter. Signals are carried by trunk cables to the utilization sites, which
may be several kilometres away. Feeder amplifiers are installed at various
places along the line to compensate for signal attenuation caused by cable
loss.
The signal attenuation that happens as a result of
cable failure. Multicore coaxial cables are used to distribute signals from splitters
to tap-off locations. A splitter is a resistive-inductive device that offers
impedance matching and trunk line isolation. Transformer-coupled,
capacitive-coupled, or resistive-pad subscriber taps are all possibilities.
They avoid mutual interference by providing
separation between receivers on the same line. Normally, taps are positioned on
the wall. Wall taps are available with 300 Ω, 75 Ω, or dual outputs. Standing
waves will form as a result of poorly terminated lines. Each 75 Ω distribution
cable is terminated by a 75 Ω resistor called a terminator to prevent
standing waves.