Stereo presence signal for an AM stereo system

Details Stereo presence signal for an AM stereo system Stereo presence signal for an AM stereo system

1977-09-27

1979-06-26

Olms, Douglas W.

H04H 500

Patent

active

041593987

ABSTRACT:
In an AM broadcast transmitter, an infrasonic tone is added to the difference channel of a compatible AM stereo system to provide a stereo presence signal. In a stereophonic receiver, the corrected output of a synchronous detector in the difference signal channel is coupled to an infrasonic detector for control of a mono/stereo mode switch and a stereo presence indicator. When the received signal is weak, the infrasonic tone is effectively stronger, because the phase angle is increased. Since the s
ratio is proportional to the phase angle, the stereo presence signal is self-adjusting. The mode switch and indicator are enabled for all values of L and R. The infrasonic tone could also be removed from the transmitted signal whenever the difference signal goes above a predetermined level during stereo broadcasting, in which case a comparator at the receiver would enable the mode switch and indicator upon detection of either a difference signal or the infrasonic tone.

REFERENCES:
patent: 3068475 (1962-12-01), Avins
patent: 3080453 (1963-03-01), Avins
patent: 3534172 (1970-10-01), Weeda
patent: 3823268 (1974-07-01), Modafferi
patent: 3908090 (1975-09-01), Kahn
patent: 4018994 (1977-04-01), Kahn
patent: 4037057 (1977-07-01), Ogita et al.

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