Abstract: A digital to analog converter utilizes a digital missing pulse detector as a time interval measuring means in which the detector includes a programmable counter, the count of which is set to correspond with the digital number or word to be converted. Clock pulses at a high frequency are applied to advance the programmable counter from a reset condition to a terminal or output condition, and the time interval produced depends upon the binary word or number set into the programmable counter. Pulses at a second lower frequency, equal to the repetition rate of the system, are applied to the input of the time interval measuring circuit; so that the output is a series of pulse width modulated pulses having a duty cycle corresponding to the binary word originally set into the programmable counter.

Abstract: Auxiliary signals suitable for conveying additional audio signals for stereophonic television broadcasts, bilingual sound, and the like, are transmitted in the form of modulated bursts of such auxiliary signal placed on the front porch of the composite video signal and continued through the vertical synchronization pulse intervals. At the receiver, a transmission gate is connected to receive the composite video signal and has an output coupled to an auxiliary signal demodulation circuit. The transmission gate is operated to pass only the auxiliary signal bursts in response to control signals obtained from the sweep circuit of the television receiver. By utilizing composite AM/FM modulation of the auxiliary signal or by employing quadrature modulation, dual or stereophonic sound signals may be obtained for reproduction with corresponding output utilization circuitry.

Abstract: An improved vertical synchronization system for a television receiver provides both good noise immunity and improved interlace. This is achieved by employing two parallel vertical synchronization circuits between the synchronizing signal input of the vertical oscillator and synchronizing signal source. One of these vertical synchronizing circuit paths comprises a standard integrator circuit adjusted for optimum noise immunity and the other is a cascaded digital circuit adjusted for improved interlace but having poorer noise immunity than the first circuit. The digital circuit produces a synchronizing pulse slightly ahead of the pulse produced by the conventional circuit so that the digital circuit normally controls the operation of the oscillator. Whenever extreme noise conditions exist, the digital circuit is disabled and the conventional synchronizing signal circuit takes over the synchronizing task.

Abstract: A four channel FM system is described. In one embodiment the usual 19 kHz pilot signal is employed to switch between front and rear information, while in another, a 76 kHz switching signal is employed for this purpose.