Synchronous and Exalted-Carrier Detection in Television Receivers

In the conventional envelope detector, shown in Fig. 1a, the picture information contained in the sidebands is demodulated by rectification of the envelope formed by the carrier and the sidebands. As the signal strength falls, the signal becomes progressively lost in the continuous noise spectrum characteristic of galactic, antenna, and tuner noise. The rectification of this noise produces a d-c component which prevents the detection of white picture information below this d-c level.