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JPS4913403

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DESCRIPTION JPS4913403
■ FMFM stereo receiver Akira Akira 45-48821 [phase] Application Akira 45 (1970) June 6 @
inventor Nakamura Tadashi-Kakushin type large letter Kadoshin 1006 Matsushita Electric
Industrial Co., Ltd. Naohiro Shibata Dosho Okubo Tsuneo Okubo The same office 0 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
receiver in which the lamp for stereo display is lit only when a stereo signal is received and the
lamp for stereo display is not lit due to inter-station noise. The present invention is a circuit for
lighting or extinguishing a lamp for stereo display using a positive feedback amplifier which is
turned on or off by a direct current heat generated by a red light in a half wave signal obtained
by half-wave rectifying a pilot signal of 1'9 KHz. And a switching transistor connected in parallel
to a circuit for extracting a direct current component in the H2 half wave signal and feeding it to
the positive feedback amplifier, a narrow band ceramic filter of 19 KH2, and ON or OFF
depending on the presence or absence of a 19 KHz signal. By switching the switch transistor off
during tuning and turning it on during non-tuning, the lamp for stereo display lights up only
when a stereo signal is received, and inter-station noise is large The lamp does not light up when
it is not synchronized. The embodiment shown in the figure will now be described in more detail
[111111]. In the figure, an FM stereo broadcast signal passes through an antenna 1 and is
received by an FM tuner 2 and detected. Among the stereo synthetic signals obtained after
detection, the 19 KHz pilot signal is converted to 38 KH 2 by the 38 KH 2 forming circuit 4. On
the other hand, the synthesized signal is amplified by the synthesized signal amplification circuit
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3 and then separated into left and right signals by the switching type demodulation circuit 6
utilizing the above-mentioned 38 KHz, and taken out from the output terminals 7 and 8. At this
time, the blinking operation of 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, reference numeral 13 denotes a diode
for providing an appropriate bias to the base of the trans jitter 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. トランジスタT4のコレ。 A 38 KH2 tuner consisting of a coil 20 and a capacitor
21 is connected to the lid, and 38 KH2 is selectively amplified by the amplifier consisting of the
transistor T4 and the tuner consisting of the coil 20 and the capacitor 21.
Thus, a 38 KH 2 switching carrier is formed and supplied to the switching system demodulation
circuit 6 from the coil 22 coupled to the coil 20. On the other hand, a resistor 25 and an
electrolytic capacitor 26 are connected to the emitter of the transistor T4, and the pilot signal is
transmitted from the transistor T2. When half-wave rectified by T3, the DC type [111111]
EndPage: 1 pressure is generated at both ends of the resistor 25 and the capacitor 26 through
the diodes 16 to 19 and the transistor T4. This DC voltage is added to the positive feedback
amplifier 5 which is turned on or off in response to the presence or absence of the DC voltage,
and the circuit of the lamp L for stereo display is turned on or off via the transistor T6. Thus,
when a stereo signal is received, the stereo display lamp is turned on. However, in a receiver with
a large number of FM intermediate frequency steps, noise generally increases suddenly when
tuning is not performed, and this inter-station noise causes a disadvantage that the lamp for
stereo display lights up. That is, even when receiving monaural broadcasts, there is a
disadvantage that the stereo display lamp is turned on by inter-station noise due to inter-station
noise, resulting in erroneous display for the listener. The present invention eliminates such a
drawback that the lamp for stereo display lights up due to the inter-station noise. In the present
invention, the 19KH2 signal taken out from one end of the 19KH2 tuner consisting of the coil 11
and the capacitor 12 is added to the second positive feedback amplifier 10 through the 19KH2
narrow band semifilter 9 and the diode 27, and the output is The switching transistor T5
connected in parallel with the resistor 25 and the capacitor 26 is turned on or off by the positive
feedback amplifier 50 manually, thereby suppressing the lighting of the lamp L due to the interstation noise. That is, at a place where the receiver is in the untuned state and inter-station noise
is large, by using the 19 KH2 narrow band ceramic filter 9, the second feedback rl111 111
feedback amplifier 10 is in the off state, then the switch transistor T , Is shorted, the DC voltage
across the resistor 25 and the capacitor 26 becomes almost zero, and the stereo display lamp L
does not light. On the other hand, at the time of tuning when a stereo signal is received, the
second positive feedback amplifier 10 is turned on since the 19KH2 signal appears at its output
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end through the 19KH2 narrowband ceramic filter 9, and thus the transistor T5 is turned off. A
direct current voltage is generated at both ends of the capacitor 26 and the lamp for stereo
display is lit.
As described above, according to the present invention, the lamp for stereo display is turned on
only when a stereo signal is received, and the lamp is not turned on at the time of non-tuning, ie,
when inter-station noise is large, so erroneous display is not given.
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