Vestigial sideband modulation
The vestigial sideband modulation is a variant of the amplitude modulation . It allows transmission with a small bandwidth with higher signal quality and little circuit complexity for the demodulator. For this purpose, one of the two sidebands is suppressed except for a remainder in the transmitter via a filter after the modulator . The carrier oscillation is only transmitted with reduced power and the second sideband is not attenuated. It can thus be described as "partial" single sideband modulation (with single sideband modulation, one sideband and the carrier are completely filtered out).
The main reason for this variant are the simpler filters behind the modulator , because they do not have to have a rectangular transmission curve in order to "cut off" the undesired sideband exactly.
The remaining sideband modulation is used, for example, when transmitting analog television signals, since the sidebands are very close to the carrier frequency. This occurs when the signal modulated onto the carrier frequency contains components of low frequency or DC components (for television: medium brightness of the picture) are to be transmitted.
In interaction with a bandpass filter with a special flank shape ( Nyquist flank ) used in the receiver , signal processing can be simplified , especially at low modulation frequencies . One application is e.g. B. the amplitude-modulated video signal in television broadcasting .