Abstract: An FM receiver as used in communciations systems includes a blanking switch for deleting noise pulses and a delay device for delaying the detected pulses so that blanking can occur at the correct time. The circuit receives and detects noise pulses and amplifies them at several gain levels simultaneously. Each amplified pulse which passes a predetermined level causes a trigger signal pulse to be coupled to a ramp generator. The trigger signal pulses are coupled through a combination of flip-flops and voltage controlled switches, and each noise pulse enables a ramp signal of a predetermined maximum but having a rise time which is a function of the detected noise pulse amplitude. The ramp signal length is used to provide blanking switch control signals of an appropriate length to blank out substantially all significant noise pulses.

Abstract: A mobile radio receiver employs an SAW filter to provide an appropriate time delay to enable an extender to effectively blank the recovered signal thereby preventing noise from entering the IF section of the radio. The SAW filter allows long signal delays without significant pulse stretching while also allowing narrow IF bandwidths. The control pulse to the blanker switch is shaped to reduce the coupling of noise generated within the blanker switch from the received signal path. The operation of the extender is controlled by the main receiver through an AGC signal to determine when, and to what extent, the extender is enabled.