Abstract: Controllable bandwidth IF filter circuit for radio receivers generally, but having particular application to quadraphonic radio receivers intended for use in a quadraphonic system that is compatible with existing monophonic and biphonic equipment, said filter circuit being automatically adjusted in a digital manner to exhibit one of several different bandwidths in response to a pair of transmitted control signals present in the quadraphonic transmission so as to provide optimum receiver operation for the particular mode of broadcast being received, especially in terms of an improved protection ratio and signal to noise ratio for the received signal. The noted bandwidth adjustments are accomplished by modifying the values for certain of the component in the filter's tuned circuit and coupling sections through their selective connection into the circuit by means of semiconductor switching devices operated in response to said pair of control signals.

Abstract: A broadcast system capable of transmitting and receiving a broadcast signal containing four discrete stereophonically related audio frequency inputs in which there is produced within the transmitter four matrix outputs, each of which is a function of one or more of the inputs. A main carrier wave is then frequency modulated with the first matrix output, with the sidebands of a suppressed first and second subcarrier which has been amplitude modulated with the second and third matrix outputs in quadrature relationship with each other, and with the lower sideband and a relatively small portion of the upper sideband of a depressed third subcarrier that has been amplitude modulated with the fourth matrix output. The modulation of the third subcarrier is limited to a maximum voltage level substantially below the highest level otherwise possible. The first, second, and third subcarriers are regenerated in the receiver and the four matrix outputs are detected.

Abstract: An intermediate frequency amplifier stage includes a tuned circuit which is shunted by a transistor utilized as an emitter follower, the emitter follower being responsive to the amplitude of a detected signal to lower the "Q" of the tuned circuit as the amplitude of the detected signal increases and to increase the "Q" of the tuned circuit as the amplitude of the detected signal decreases, thus effecting the gain of the intermediate frequency amplifier stage inversely respective the amplitude of the detected signal.