GB1007314A - Receiver for a stereo fm multiplex system - Google Patents

Abstract

1,007,314. Stereophonic radio receiving systems. LOEWE OPTA A.G. July 9, 1962 [Aug. 11, 1961], No. 26169/62. Heading H4L. Relates to a receiver for the reception of stereophonic broadcast signals of the type in which an (L-R) signal is transmitted as an amplitude modulation of a subcarrier, the subcarrier being suppressed and a pilot signal at half the subcarrier frequency transmitted. As shown in Fig. 1, after demodulation of the L+R signal, the combined L+R signal, suppressed carrier L-R signal and pilot signal are supplied to the control grid of a valve 1 thus energizing a frequency-doubling circuit 2 tuned to the frequency of the pilot signal. Frequency doubled half-waves are fed to the control grid of a valve 7 and energize a circuit 8 tuned to the subcarrier frequency, feedback circuits 9, 10 being adjustable so that this stage can operate either as a synchronized oscillator or a selective amplifier. Alternatively it may be adjusted so that the stage only oscillates when the frequency doubled signal is applied to the control grid. The reconstituted subcarrier is supplied via capacitors 14, 15 to respective deflecting plates 16, 17 of a beam deflecting tube 18, the multiplex signal from the cathode circuit of valve 1 being supplied to the control grid of the tube 18. The demodulated, L - R signal appears in antiphase at the respective anodes of the tube 18 while the L + R signal is in phase at both anodes, the resultant signals at the respective anodes being the L and R signals respectively. A portion of the multiplex signal from the cathode of the tube 18 is combined with the output signals via potentiometers 25, 26 to compensate for crosstalk. A potentiometer 27 provides an adjustment for correct balance between the two channels. In an alternative arrangement, Fig. 2 (not shown), two pairs of oppositely poled diode switches are used instead of the beam deflection tube and are switched alternately by the subcarrier to produce the left and right signals. The subcarrier regenerator also is modified in that positive feedback is supplied via the screen grid instead of the control grid of valve 7.