Abstract: A circuit is described for maintaining an input signal to a limiter used to limit amplitude excursions of a signal to be angle demodulated. Means are provided for detecting a temporary loss in signal to said limiter resulting from the loss of signal due to large negative amplitude modulation or other factors. When the amplitude of the angle modulated wave falls below a predetermined minimum, a substitute intermediate frequency signal is generated to maintain the limiter in a limiting condition during the temporary loss in broadcast signal. The substitute intermediate frequency signal has a frequency substantially equivalent to the intermediate frequency signal developed from the broadcast signal during periods when the amplitude of the broadcast signal is adequate. The substitute signal prevents the occurrence of noise generated from an angle demodulator due to a temporary loss in signal.

Abstract: A superheterodyne receiver is described for demodulating signals containing both amplitude and angle modulation components. An intermediate frequency signal is produced which is simultaneously amplitude detected as well as angle demodulated. Detector means are provided for detecting the occurrence of high negative amplitude modulation peaks of the broadcast signal. During high negative amplitude modulation peaks, the angle demodulator output is held at a fixed level until the amplitude of an input signal is restored to a predetermined minimum level.

Abstract: Apparatus is described for transmitting and receiving stereophonic broadcasts in the low frequency commercial AM broadcast band. A transmitter is described which modulates the phase and amplitude of a broadcast signal with separate information signals. A pilot tone may also be included to identify the transmission as stereophonic. Receiving means for detecting the PM and AM components to derive separate signals for stereophonic reception are included.

Abstract: An improved tuning system for a color television receiver embodying a varactor tuner having a controller functioning as a potentiometer to provide a preselected tuning voltage for channel selection. The system includes a tuning voltage supply having a low impedance drive which is serially connected at its output with the controller. The voltage supply applies a preselected source voltage to the controller which is substantially independent of changes in the resistive value of the controller. The tuning voltage supply is combined with automatic fine tuning correction circuitry connected between the automatic fine tuning system and the varactor tuner. The automatic fine tuning correction circuitry applies a correction voltage to the varactor tuner for temperature compensation, fine tuning errors of 500 KHZ or less, etc.