Abstract: An improved circuit for producing a signal indicative of an input signal floor level is disclosed for use in determining the noise level of an audio signal in a receiver voting system. An input audio signal which contains noise is amplified by variable gain amplifier circuitry consisting of a constant gain amplifier and a variable attenuator. Detector circuitry then develops a signal which is indicative of the noise level, this signal substantially corresponding to the minimum peak magnitude of the amplified input audio signal. During pauses between audio tones in the input audio signal, this minimum signal magnitude coincides the residual background noise level of the input audio signal. Control circuitry couples the noise level indicative signal to the variable attenuator and constitutes a negative feedback loop for inversely and nonlinearly varying the amplification of the input signal in response to the magnitude of the noise indicative signal.

Abstract: An improved receiver voting system is disclosed in which the lowest noise audio signal produced by a number of different radio receivers is selected and coupled to a monitoring speaker. Each receiver receives signals from a transmitter and produces either corresponding audio signals or squelch indicating status tones which are then transmitted to a voting (selecting) control center by telephone communication lines. The voting control center then selects the unsquelched receiver audio signal having the lowest noise level and couples this signal to a monitoring speaker.The voting center indicates which receiver is supplying the selected signal and therefore identifies the most favorable receiver to transmitter signal path. Parallel squelch circuits in each receiver provide for the initial selection of the strongest received signal while preventing the existence of an irratating "squelch tail.