Abstract: A scrambler for a television system alternately inverts the phase of the carrier which is modulated by the television signal. A binary coding signal controls the manner of the carrier-phase inversion. Phase inversion is obtained by combining the modulated normal carrier with an out of phase carrier having a maximum peak amplitude greater than the peak amplitude of the modulated carrier. The coding signal also frequency modulates the carrier for the scrambled television signal thereby providing a key for decoding at the television receiver. The decoder at the receiver reproduces the coding signal from the scrambled signal, removes the frequency modulation and combines the scrambled signal with a reproduced normal carrier at the time intervals corresponding to the presence of the phase-inverted carrier.

Abstract: An improved scrambler and decoder for a television signal is described wherein a television carrier is inverted in phase and subjected to low frequency amplitude modulation to obtain enhanced channel security. The carrier amplitude modulation is obtained with a coding signal which is transmitted as a pilot signal in the form of frequency modulation of the carrier. The coding signal is recovered at the decoder with a phase lock network and used to regenerate an unscrambled carrier. The coding signal provides information for special functions such as subscriber access control, program selection and the like.