05-07-2012, 02:37 PM
TV Transmission Principles
TV Transmission Principles.ppt (Size: 1.37 MB / Downloads: 67)
Problem Statement
Efficient transmission of color information in a TV signal
Type of modulation appropriate for signals that have a strong low-frequency component, such as video signals
Image/Picture transmission in TV signals
Baseband vs. Passband Transmission
Baseband signals:
Voice (0-4kHz)
TV (0-6 MHz)
A signal may be sent in its baseband format when a dedicated wired channel is available.
Otherwise, it must be converted to passband.
Modulation & Demodulation
TV broadcast
The audio signal
symmetrical signal
without continuous current
frequency does not exceed 20 kHz.
The video signal
consists of a logical component, the sync and an analogue part according to the line picture scanning
unsymmetrical signal
continuous component
frequency bandwidth extends from 0 to 5 MHz.
Modulation Type
In television though positive modulation was adopted in initial stages, negative modulation is generally adopted (PAL’B uses negative modulation) now a days, as there are certain advantages over positive modulation.
Advantages of Negative Modulation
The peak level representing the blanking or sync level may be maintained constant, thereby providing a reference for AGC in the receivers.
In negative modulation, the peak power is radiated during the sync-tip. As such even in case of fringe area reception, picture locking is ensured, and derivation of inter carrier is also ensured.