Abstract: A local oscillator suitable for integrated circuit construction in a radio receiver maintains low level voltage oscillations across a tank circuit which may include a varactor diode. An emitter-coupled pair of transistors with a small switch-over voltage has the collector of the second transistor connected to the base of the first. Third and fourth matching transistors have emitters connected to the bases of the second and first transistors, respectively, and grounded collectors. The base of the third transistor is connected through a diode to ground; while the base of the fourth transistor is connected through a matching diode and the tank circuit to ground. A source of electric power having a voltage greater than two diode drops above ground is effective to supply current through resistors to the bases of the first and second transistors.

Abstract: A radio receiver includes apparatus for attenuating the audio signal derived from weak and noisy radio frequency signals to render the resulting noisy output audio signals less objectionable. Apparatus is provided to attenuate the AGC audio frequency signal in a predetermined constant attenuation, linearly mix the AGC regulated and attenuated audio frequency signals in a proportion controlled by an attenuation control signal and generate the attenuation control signal from the difference between the radio AGC signal and a predetermined constant reference.