Noise reducing

A noise reducing AM receiver comprising,

• a receiving stage for receiving an AM signal of carrier frequency separated from that in an adjacent channel by a predetermined spacing,
• a quadrature detector coupled to said receiving stage for detecting a quadrature signal from said received AM signal,
• an in-phase detector coupled to said receiving stage for detecting an in-phase signal from said received AM signal,
• a band-reject filter coupled to said quadrature detector for providing a filtered version of said quadrature signal, said band-reject filter characterized by a center frequency corresponding to said predetermined spacing,
• a full-wave rectifier coupled to said band-reject filter for rectifying said filtered version of said quadrature signal,
• a comb filter coupled to said full-wave rectifier, said comb filter including a recirculating delay line and being tuned to a local AC line frequency and its harmonics,
• a noise detector coupled to said comb filter for detecting the presence of a predetermined amount of noise in the signal passed by said comb filter for providing a blanking control signal in the presence of at least said predetermined amount of noise, said noise detector including a source of a threshold signal representative of said predetermined amount of noise and a comparator coupled to said comb filter and to said source of a threshold signal, and
• a first noise blanker responsive to said blanking control signal to process said in-phase signal, said first noise blanker including an all-pass filter and a low-pass filter coupled to said in-phase detector, and a switch for selecting between said low-pass filter and said all-pass filter in response to said blanking control signal in order to process said in-phase signal by providing a reduced bandwidth output signal in the presence of at least said predetermined amount of noise.

A noise reducer, comprising

• a signal input for receiving an input signal,
• a control input for receiving a blanking control signal,
• an all-pass filter coupled to said signal input and including an all-pass output, said all-pass filter being adapted to filter said input signal and provide a resulting all-pass-filtered signal on said all-pass output,
• a low-pass filter coupled to said signal input and including a low-pass output, said low-pass filter being adapted to filter said input signal and provide a resulting low-pass-filtered signal on said low-pass output, and
• a switch coupled to said control input, said low-pass output and said all-pass output, said switch being adapted to select between said all-pass and said low-pass outputs in response to the blanking control signal to provide a reduced bandwidth output in the presence of said blanking control signal.

A noise blanking AM receiver comprising,

• a receiving stage for receiving an AM signal of carrier frequency separated from that in an adjacent channel by a predetermined spacing,
• a detecting stage coupled to said receiving stage for detecting at least a first portion of the received AM signal that may have noise,
• a noise discriminator coupled to said detecting stage for providing an indication of the presence of noise in at least a first portion of said received AM signal, and
• an adjustable filter coupled to said noise discriminator for filtering at least a second portion of the received AM signal to reduce the bandwidth of at least said second portion in response to the level of noise present in at l east said first portion.

A method of processing a received AM signal comprising the steps of:

• providing a low-pass-filtered version of the received AM signal,
• providing an all-pass-filtered version of the received AM signal, and
• selecting said all-pass-filtered version during normal operation,
• and selecting said low-pass-filtered version in the presence of a predetermined amount of noise during abnormal operation.