stereofonischer receiver with a device for the production of a anzeigespannung in's dependence on whether or not the empfangssignal stereofonisch

摘要

992,684. Stereophonic radio receiving systems. HAZELTINE CORPORATION. Feb. 5, 1963 [Feb. 26, 1962], No. 4682/63. Heading H4L. A radio receiver for stereophonic or monophonic signals is provided with means for deriving an indication of the presence or absence of stereophonic signals in the received signal whereby the stereophonic circuits are disabled in the absence of a received stereophonic signal. As shown in Fig. 1, in a system in which the L + R signal frequency modulates a main carrier and the L-R signal amplitude modulates a 38 kc/s. subcarrier which is suppressed, a 19 kc/s. pilot signal being transmitted, the output of the frequency discriminator. 13 is supplied to a known type of stereophonic adapter 14 comprising a local oscillator and phase-splitter 18 synchronized by the 19 kc/s. pilot signal to provide a 38 kc/s. switching signal for demodulating and separating the L and R signals at 21. The composite stereophonic signal is supplied via a filter 19 blocking the pilot signal and a filter 20 blocking an additional (storecast) signal, to the demodulator 21, the L and R signals being supplied via a deemphasis network 22 to the respective output circuits. The output from 13 is also supplied via an amplifier 31 having an output circuit 36 tuned to select the 19 kc/s. pilot signal which is supplied to a detector 37 providing one of two voltage levels depending on the presence or absence of the pilot signal. The output of the detector 37 is supplied to a D.C. amplifier 40 which is arranged to be biased negatively when the pilot signal is present so that its rise of anode potential causes a neon indicator 52 to strike. This bias is removed for monophonic signals so that the anode potential of valve 40 is decreased and the neon lamp 52 is extinguished, a potentiometer 50 being adjusted so that the voltage at the movable tap is higher than the anode voltage of the valve 40 but lower than the maintaining voltage of tube 52. Thus diodes 47, 48 will conduct and the tank circuit of oscillator 18 will be heavily loaded by capacitors 51, 45, 46 so that the oscillator will be inoperative. When the stereophonic signal is present, diodes 47, 48 will be reverse-biased due to the increase in anode voltage of the valve 40, thereby removing the loading from the tank circuit of the oscillator 18. Any variation of the reverse bias which could cause a phase shift in the oscillator 18, is prevented by the tube 52 acting as a voltage regulator. In a further modification, Fig. 3 (not shown), in which the stereophonic adapter is of the type comprising a frequencydoubler providing a subcarrier signal for combination with the L-R sidebands, the recombined L-R signal is supplied to a double diode demodulator and matrix circuit together with the L + R signal, the connection between the recombined L-R signal and the demodulator being controlled via a diode switch in a similar manner to that shown in Fig. 1.