US 4,358,638 A · Apparatus for receiving an AM stereophonic signal

Abstract

Apparatus for receiving an AM stereophonic signal of the type having monaural information represented by amplitude modulations of a signal carrier and stereophonic information represented by phase modulations of the signal carrier. A reference signal generator generates a reference signal that is synchronized with the signal carrier of the received AM stereophonic signal. In one embodiment, the reference signal generator is a phase-locked loop which generates a reference carrier whose frequency is substantially equal to the signal carrier frequency and whose phase is locked to a predetermined signal carrier phase. An amplitude limiter limits the AM stereophonic signal to remove amplitude modulations of the signal carrier and thereby produce an amplitude-limited signal carrier. A demodulator demodulates the information represented by the AM stereophonic signal, and a detector is provided to detect if the stereophonic information will be properly demodulated. A switching arrangement is controlled by the detector to supply the reference signal to the demodulator, whereby the stereophonic information is demodulated, or to supply the amplitude-limited signal carrier to the demodulator, whereby the monaural information is demodulated.

Claims17

Dependent claims

amplitude limiter means for limiting said AM stereophonic signal to remove amplitude modulations of said signal carrier and thereby produce an amplitude-limited signal carrier;
demodulating means for demodulating the information represented by said AM stereophonic signal;
means for supplying said AM stereophonic signal to said demodulating means;
switch means having a first state for supplying said reference signal to said demodulating means, whereby said stereophonic information is demodulated, and a second state for supplying said amplitude-limited signal carrier to said demodulating means, whereby said monaural information is demodulated;
detecting means for detecting when said stereophonic information will not be properly demodulated to produce a control signal;
and switch control means responsive to said control signal for changing over said switch means from said first state to said second state.

3 more elements

Apparatus for receiving an AM stereophonic signal of the type carrying monaural information and stereophonic information, said apparatus comprising an IF stage for producing an IF AM stereophonic signal;

phase-locked loop means supplied with said IF AM stereophonic signal to generate a reference carrier whose frequency is substantially equal to the frequency of the IF signal carrier and whose phase is locked to a predetermined phase of the IF signal carrier;
amplitude limiter means for limiting said IF AM stereophonic signal to remove amplitude modulations of said IF signal carrier and thereby produce an amplitude-limited signal carrier;
synchronous detecting means for demodulating the information carried by said IF AM stereophonic signal;
phase-lock detecting means for detecting if said phase-locked loop means is phase-locked with said IF signal carrier;
and switch means operative to supply said reference carrier to said synchronous detecting means if said phase-locked loop means is phase-locked with said IF signal carrier, whereby said stereophonic information is demodulated, and operative to supply said amplitude-limited signal carrier to said synchronous detecting means if said phase-locked loop means is not phase-locked with said IF signal carrier, whereby said monaural information is demodulated.

2 more elements

phase-locked loop means supplied with said IF AM stereophonic signal to generate a reference carrier whose frequency is substantially equal to the frequency of the IF signal carrier and whose phase is locked to a predetermined phase of the IF signal carrier;
amplitude limiter means for limiting said IF AM stereophonic signal to remove amplitude modulations of said IF signal carrier and thereby produce an amplitude-limited signal carrier;
synchronous detecting means for demodulating the information carried by said IF AM stereophonic signal;
signal level detecting means for detecting the intensity level of said IF AM stereophonic signal;
and switch means operative to supply said reference carrier to said synchronous detecting means if the intensity level of said IF AM stereophonic signal exceeds a threshold, whereby said stereophonic information is demodulated, and operative to supply said amplitude-limited signal carrier to said synchronous detecting means if the intensity level of said IF AM stereophonic signal is less than said threshold, whereby said monaural information is demodulated.

2 more elements

Dependencies are inferred from the claim text.

Apparatus for receiving an AM stereophonic signal

Life of this patent

Apparatus for receiving an AM stereophonic signal

Life of this patent

Abstract

Claims17