Multiplex signal receiver

• US 4,361,728 A
• Filed: 04/09/1980
• Issued: 11/30/1982
• Est. Priority Date: 04/13/1979
• Status: Expired due to Term

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Tanabe, Kenzo
• Primary Examiner(s): Masinick, Michael A.
• Assistant Examiner(s): COLES, EDWARD L
• Application Number:
  US06/138,515
• Time in Patent Office: 965 Days
• Field of Search: 179/1 GS, 329/110, 329/146, 329/50, 329/121
• US Class Current: 370/204
• CPC Class Codes: H04H 20/49 for AM stereophonic broadcast systems
• CPC Class Codes: H04H 40/36 specially adapted for stereophonic broadcast receiving

Abstract

A superheterodyne type multiplex signal receiver for multiplex signal transmission systems for receiving two independent signals transmitted by amplitude modulation and angle modulation of single carriers, and for detecting an intermediate frequency by an intermediate frequency detector when changing the local oscillating frequency by a dial operation to select the received signal. The receiver has a switching circuit so composed that it operates a demodulation circuit which demodulates, from the modulated carrier, the two independent signals, which are then transmitted to two independent audio amplifiers provided at a later stage of an intermediate frequency amplifier for driving two speakers for reception of the multiplex signal, when the intermediate frequency is extremely close to a normally determined frequency. The switching circuit also transmits to the two independent audio amplifiers the demodulated signals obtained from an envelope detection circuit when the intermediate frequency is remote from the normally determined frequency.

Claims

1. A multiplex signal receiver used for multiplex signal transmission systems which transmit two independent signals by amplitude modulation and angle modulation of a single carrier, said receiver comprising:

a switching circuit;

an angle demodulator for demodulating an angle modulated signal component of a signal received by said receiver;

an envelope detector for demodulating an amplitude modulated signal component of said received signal;

an intermediate frequency detector for detecting an intermediate frequency and for outputting a control signal for controlling said signal switching circuit; and

a matrix circuit for modifying an output signal of said angle demodulator and an output signal of said envelope detector by addition and subtraction thereof so as to obtain two output signals for driving a two channel amplifier through said signal switching circuit;

wherein said signal switching circuit is supplied with said two output signals of said matrix circuit and the output signal of said envelope detector and selects as its output signals either said two output signals of said matrix circuit or said output of said envelope detector according to said control signal;

and wherein said selection of the output signals of said signal switching circuit is dependent upon the closeness of said intermediate frequency to a predetermined frequency, and wherein the frequency range of said intermediate frequency for selecting said two output signals of said matrix circuit as the output signals of said signal switching circuit is set according to the characteristics of an intermediate frequency filter included in said intermediate frequency detector.

2. A multiplex signal receiver according to claim 1, wherein means are provided for adding hysteresis characteristics to said signal switching circuit.

3. A multiplex signal receiver according to claim 1, wherein a display element is connected to said signal switching circuit for indicating a state of exact tuning.