3
Polarisation
In order to increase the number of channels in each satellite slot the signals are
transmitted with different polarisation. Two kinds of polarisation are used in TV
transmissions: linear and circular.
Linearly polarised signals propagate with their wavefronts aligned either horizontally
or vertically. The receiving LNB can then separate the two polarisations if it is aligned
properly.
Circularly polarised signals propagate with their wavefronts rotating either clockwise
or counter-clockwise
The main advantage with linear polarisation over circular is that the isolation between
the two modes is better. The main advantage with circular polarisation is that the
feedhorn doesn't need to be aligned.
Chapter 1: General information
Polarisation
