Abstract: An FM detection system receives an FM input signal containing a plurality of carrier bands, including a tuned carrier band. The tuned carrier band is separated from side carrier bands by a frequency guard band. A detected, demodulated output signal is fed back to at least one local oscillator, which generates corresponding local FM signals having a deviation which is in phase with the deviation of the tuned carried. The FM input signal and the local FM signal are inputs to a guard band expansion device. The guard band expansion device includes a harmonics generator which produces an output spectrum which is a multiple of its input spectrum. In one embodiment, the harmonics generator operates directly on the FM input signal, its output signal then being beat by a mixer with the local FM signal. In another embodiment, the operations of harmonics generation and mixing are reversed.

Abstract: Disclosed is a Class A power amplifier circuit which includes means for controlling the quiescent bias current of the output devices of the amplifier and providing absolute overload and short circuit protection without the need of extra protective devices of any kind. The circuit includes a driver stage which amplifies an input signal and provides two outputs which are out of phase with respect to each other by 180.degree.. One output of the driver stage provides a drive signal to the control input of a first output device, while the other output of the driver stage provides a drive signal to the control input of a second output device. Power is provided to the driver stage by a standard grounded center-tapped power supply.