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JPS4913402

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DESCRIPTION JPS4913402
■ FM FM stereo broadcast receiver No. 45-48820 [phase] Application No. 45 (1970) June 6 @
inventor Nakamura Tadashi-Kadoma city Ogata Kadoma 1006 Matsushita Electric Industrial Co.,
Ltd. Naohiro Natona Dokdo Dojo Okubo Toshio The same office ■ Applicant Matsushita Electric
Industrial Co., Ltd. Kadoma city Oji Kadoma 1006 [Fa] Agent patent attorney Yoji Yoshizaki
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram of an embodiment of the
present invention.
DETAILED DESCRIPTION OF THE INVENTION The present invention provides an FM stereo
broadcast receiving apparatus in which a stereo display lamp is turned on only when a stereo
signal is received, and the stereo display lamp is not turned on by inter-station noise. It is. The
outline of the present invention is for stereo display using a positive feedback amplifier which is
turned on or off according to the presence or absence of a DC component contained in a half
wave signal obtained by half wave rectifying a 19 KHz FM stereo broadcast pilot signal. In a
circuit for turning on or off the lamp, a switching transistor is connected in parallel with the
input circuit of the positive feedback amplifier, and the output voltage of the FM muting circuit is
applied to the switching transistor, and the switch is used when the receiver is tuned. By turning
off the transistor and turning it off when not tuned, the lamp for stereo display is turned on only
when a stereo signal is received, and the lamp is not turned on when there is a large amount of
inter-station noise. [111111] Next, the embodiment shown in the figure will be described in more
detail. First, the schematic configuration and operation of the FM stereo broadcast receiving
apparatus of the present invention will be described. In the figure, an FM stereo broadcast signal
is received by an FM tuner 2 via an antenna 1 and detected there once. Among the stereo
synthetic signals obtained after detection, the 19 KHz pilot signal is converted to 38 KH 2 by the
38 KHz forming circuit 4. On the other hand, the synthesized signal is amplified by the
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synthesized signal amplifier circuit 3 and then separated into the left signal and the right signal
by the switching type demodulation circuit 6 utilizing the above-mentioned 38KH2 and taken out
from the output terminals 7 and 8. At this time, the operation for turning on and off the stereo
display lamp is performed as follows. That is, in the 38 KH2 forming circuit 4, the 19 KHz pilot
signal is selectively amplified by the amplifier of the transistor T1, the 19 KHz tuner consisting of
the coil 11 and the capacitor 12. The pilot signal is then followed by two Darlington-connected
transistors T2. It is half-wave rectified by a 19 KH2 half-wave rectifier circuit consisting of T3. In
the figure, 13 is a diode for providing an appropriate bias to the pace of the transistor T2. A DC
voltage is generated across the diodes 16 to 19 connected to the emitter of the transistor T3 by
this half-wave rectified signal, and this DC voltage is applied to the base of the transistor T4 to
activate the transistor T4. A 38 KH 2 tuner including a coil 20 and a capacitor 21 is connected to
the collector of the transistor T 4, and 38 KH 2 is selectively amplified by the amplifier including
the transistor T and the coil 20 and a tuner including a capacitor 21. And is supplied to the
switching system demodulation circuit 6 from the coil 22 coupled to the coil 2 o.
On the other hand, the resistor 25 and the electrolytic capacitor 26 are connected to the emitter
of the transistor T4, and the pilot [111111] EndPage: 1 signal is transmitted to the transistor T2.
After being half-wave rectified by T3, a DC voltage is generated across the resistor 25 and the
capacitor 26 through the diodes 16 to 19 and the transistor T4. The step 100 is turned on or off
via the transistor T6 by using the positive feedback amplifier 5 whose presence or absence of the
direct current voltage corresponds to on or off. Thus, when a stereo signal is received, the stereo
display lamp is configured to light. [-2] However, in a receiver with a large number of FM
intermediate frequency steps, noise generally increases sharply when tuning is canceled, and this
inter-station noise causes a disadvantage that the lamp for stereo display is lit. That is, even
during monaural broadcast reception, the stereo display lamp is turned on due to inter-station
noise, resulting in a disadvantage that the listener feels wrong. SUMMARY OF THE INVENTION
The present invention provides a receiver which eliminates such a drawback that the interstation noise causes the lamp for stereo display to light. In the present invention, the output
voltage of the FM muting circuit 9 is connected in parallel to the resistor 25 and the resistor 77,
and the required transistor T5 is used in parallel. That is, as shown in the figure, the output of the
muting circuit 9 obtained by rectifying a part of the intermediate frequency output is connected
via the resistor 27 to the base of the switch transistor T5 connected in parallel with the human
power of the positive feedback amplifier 5. In addition, transistor T when the receiver is tuned to
the incoming signal. Is turned off, and when not tuned, the transistor Ts is turned on to make it
short. In this case, the DC voltage across the resistor 25 and the capacitor 260 becomes almost
zero because the transistor T5 is short-circuited when the inter-station noise is thick 5 o'clock
when not tuned, so that the positive feedback amplifier 5 is off, so the stereo display lamp 10
does not light. On the other hand, at the time of tuning, the transistor T5 is in the off state, so
that when a stereo signal is received, a DC voltage is generated across the resistor 25 and the
capacitor 260, the positive feedback amplifier 5 is turned on, and the stereo display lamp 10 is
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lit. Do. As described above, according to the present invention, the stereo display lamp is turned
on only when the stereo signal is received, and the stereo display lamp is not turned on when the
monaural signal is received or when the inter-station noise is large. Will not give a false
indication.
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