Patent
1974-07-10
1976-03-16
Olms, Douglas W.
325 36, H04H 500
Patent
active
039447499
ABSTRACT:
Amplitude modulation (AM) stereophonic transmission receivers for reception of a radiant energy carrier wave with two stereo related signals, each appearing as a first order single-sideband, the carrier wave preferably being also modulated with an infrasonic frequency (e.g. 15 Hz) signal indicating stereo signal presence (with such infrasonic frequency modulation being either amplitude modulated or phase modulated). The upper sideband and the lower sideband portions of the received signal are separately detected and through voltage comparison means are applied to the development of automatic switching control of the detector outputs to deliver as receiver outputs either stereophonically related audio signals in the presence of different upper and lower sideband detector outputs or to deliver monophonically related (i.e. combined) detector outputs in the instance of reception of a monophonically modulated carrier wave. Such voltage comparison means, operating on the respective upper and lower sideband detector outputs, is advantageously activated (i.e. gated) by the presence in at least one detector output of the infrasonic modulation signifying the presence of stereo related modulation of the carrier wave, the output from such voltage comparison means also providing, in addition to the automatic switching of the detector outputs to stereophonically related audio receiver output mode as above indicated, a visual output (suitably in the form of a stereo presence/tuning light) directly and visually indicating to the receiver operator the presence of a stereo signal, and also providing the operator with a means to tune the RF portion of the receiver accurately to the carrier frequency, the proper RF tuning being indicated by maximal intensity of the visual output. Modified forms of receiver circuitry are presented wherein, in a first instance, the IF passband is defined by a double sideband filter and the intelligence is separated into upper sideband and lower sideband portions by separate upper sideband and lower sideband filters, and, in the second instance, the IF passband is defined simply by upper sideband and lower sideband filters with a portion of the filter outputs summated and the envelope thereof separately detected to provide a monophonic audio output and an AGC signal.
REFERENCES:
patent: 3167614 (1965-01-01), Holt et al.
patent: 3206550 (1965-09-01), Fink
patent: 3218393 (1965-11-01), Kahn
patent: 3350645 (1967-10-01), Kahn
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