Digital Signal Processing Reference
In-Depth Information
negative modulation. Positive modulation is only used in the French Stan-
dard L.
The sound subcarriers are frequency modulated in most cases. To save
bandwidth, the vision carrier is VSB-AM (vestigial sideband amplitude
modulation) modulated, i.e. a part of the spectrum is suppressed by band-
pass filtering. The principle is shown in Fig. 2.10. and 2.11. Because of the
nonlinearities and the low signal/noise ratio on the transmission link, fre-
quency modulation is used in satellite transmission.
Since these analog transmission paths are losing more and more in
significance, they will not be discussed in greater detail in this topic and
the reader is referred to the appropriate literature, instead.
Power =
sync peak power
Mod.
CVBS
10% Residual
picture carrier
Vision
carrier
Fig. 2.11.
Vision modulator
2.5 Distortion and Interference
Over the entire transmission link, an analog video signal is subjected to in-
fluences which have a direct effect on its quality and are immediately visi-
ble in most cases. These distortions and interferences can be roughly
grouped in the following categories:
•
Linear distortion (amplitude and phase distortion)
•
Non-linear distortion
•
Noise
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