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NOT 461-2002-en

GHOSTING.- SHIELDING

Description: 

in many big cities the tv signal is transmitted from a tower placed in the middle of them (see figure).

in this case there is usually a line-of-sight from most of the buildings to the broadcasting antennas, and thereby the power of the tv signal is rather strong.

in situations like this it must be observed certain precautions to avoid the interference between the direct signal captured by the antenna and the one that can ingress into the distribution network through factors like:

  1. defective or corroded connections
  2. use of poor shielded coaxial cables

non loaded inputs with the corresponding 75 ohms terminator


as illustrated in the figure, the signal broadcasted from the tower might ingress into the distribution network following different paths than the off-air antenna reception pattern.

as a result, the picture in the tv screen will be affected by several lead and delayed signals that originate ghosts on both sides of it.

to overcome this problem it would be necessary either dismantling the network to install good cable&components or make use of channel converters.

a well done new distribution network will eliminate reflections because of both mismatching and ingress of external signals due to poor shielding:


the idea of the second solution is, maintaining the existing tv distribution network, translate the frequency of the tv programme (e.g. ch.55) to another frequency (e.g. ch.21) and tune the tv set to this new frequency.

hereby the channel (e.g. ch.55) being transmitted never will be of concern because now we only allow ch.21 going through the distribution network whilst the tv tuner rejects ch.55.

Id Anrterior: 
17
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