Abstract: Method and apparatus for determining loss of a received frequency modulated carrier wherein the receiver includes a limiter and discriminator and generates an AGC voltage for controlling the gain of the receiver and producing an output signal from the discriminator having an output bandwidth in excess of that required for the information channel. The unused portion of the output bandwidth is used to sample the noise level voltage through a narrow band filter which upon reaching a selected magnitude provides an indication of the loss of the carrier. The invention, in another aspect, includes a gate control of the AGC voltage which for high signal values interrupts the action of the video networks deriving the noise level voltage.

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.