Specifications

[
StarServe Installers Guide
]
page 29
The MATV Head-End
The Head End of a MATV system usually consists of an
antenna which receives broadcast signals, processing
equipment to filter the signals and a distribution amplifier to
amplify the signals to compensate for distribution losses.
Antennas, amplifiers, taps, filters and attenuates are used in
this portion of the system.
The MATV Antenna
The quality of TV reception can be no better than the quality
of the signal from the antenna. It is therefore vital to select
the correct antenna for the intended location.
Antenna manufacturers produce geographic maps detailing
preferred antenna types based on the geographic location.
In addition, professional antenna installers carry test equipment
to optimise antenna placement and orientation.
The quality and strength of any signal received is determined
by the following:-
• Proximity to the transmission tower.
• Power of the transmitter.
• Quality of the transmission.
• Line of sight to the transmission tower.
• Weather conditions.
• Interference from power lines.
• Directional characteristics and orientation of the antenna.
• Level of gain of the antenna.
Antenna Selection
The antenna installation should provide at least 0 dB (1000
µV) of picture signal per channel at the amplifier input.
In strong signal areas this will be relatively easy to obtain. In
weak signal areas a larger antenna with a high gain will usually
be necessary. It may also be necessary to “stack” two or
more antennas. Stacking two antennas will provide an
additional 3 dB of gain above the gain of a single antenna.
Although a pre-amplifier may be used, stacking before
pre-amplification is preferable, as it delivers a cleaner signal
to the system.
Antenna directivity is important. Directivity is a measure of
how well an antenna will reject signals from any direction
other than the front. The front-to-back ratio is one way of
measuring an antenna’s directivity. This is the ratio of the
amount of signal received by the front of the antenna to the
amount of signal received by the rear. A highly directional
antenna will generally have a high front-to-back ratio.
Signal Survey
Determining signal levels is one of the most important steps
in Head-End design and a signal survey before installing the
system will avoid many potential problems.
An antenna, several sections of mast, a field strength meter
and a portable colour TV is the equipment required for a signal
survey. The field strength meter measures the amount of signal
received on each channel. Carefully selected antennas can
also do much to overcome certain types of interference. The
portable TV allows the quality of the signal received on each
channel to be determined.