Reference pulses of opposite polarity to the horizontal sync pulses are added to the composite television signal just preceeding each horizontal sync pulse. The video portion of the signal is inverted for randomly selected fields. Coding bursts are added to the composite signal to indicate whether subsequent field is inverted. Transmitter clamped to reference pulse level. Reference pulse used for AGC in decoder. Video portion of received signal inverted in accordance with coding bursts. Audio program signals encoded by modulation on suppressed carrier centered above audio range. Barker signals transmitted on normal audio frequencies.