Abstract: A number of remotely mountable transmitting heads each has a transducer driven by a sweep frequency ultrasonic signal for generating an ultrasonic field. A number of remotely mountable receiving heads each processes incident doppler shifted energy reflected by a disturbance by developing therefrom a constant amplitude received signal and multiplying this signal by the ultrasonic signal to generate a pair of noise cancelling differential signals. A processor for generates the ultrasonic signal and further processes the received signals so as to detect the disturbance or system tampering.

Abstract: An equalizer in which an input signal is double differentiated without introducing phase shift. First and second differentiating circuits are provided at the input electrode and one of the output electrodes of a transistor. A further circuit is provided at the other transistor output electrode, the circuit having the same time constant as the time constant of the first differentiating circuit. Low pass filters and noise suppression may be included in embodiments particularly useful in video and audio recording and reproducing systems.

Abstract: Apparatus, including an injection lock and voltage controlled oscillator, generates a signal that follows the average frequency variations and instantaneous phase variations of a repetitive non-continuous signal. The oscillator injection lock input receives the repetitive signal and its DC control input receives an error signal generated in an AFC loop which derives the difference between the oscillator output and the repetitive signal average frequency. In one particular application, the appartus is useful in a color television signal processing or reproducing system for generating a television color subcarrier signal. The apparatus is further disclosed in connection with a demodulation-remodulation type color corrector in a video reproducing system.