JPS61116429A - Am stereo receiver - Google Patents

Abstract

PURPOSE:To use effectively an operation panel by changing over automatically the passing band width of an intermediate frequency amplifier to the wide band when a stereo broadcasting is received, and to the narrow band when the monoral broadcasting is executed, with the information obtained by the output of the stereo indicator. CONSTITUTION:An intermediate frequency band change-over device 4 selects one side input side 4A of the intermediate frequency band change-over device 4 when an intermediate band changeover control input 4c is a low level, and other side input side 4B when the input is a low level, and either of the wide band intermediate frequency or the narrow band frequency is outputted to the output 4D. A stereo demodulator 5 demodulates a stereo composite signal to the right and left sound signals, and at the time of receiving the stereo signal, an stereo indicator 6 lights up. The output of the stereo indicator 6 goes to the intermediate frequency band change-over control input 4C, and at the time of receiving the stereo signal, a low level is obtained and at the time of receiving the monoral signal, the high level is obtained and an intermediate frequency band width is automatically changed over. Thus, a malfunction and change-over forgetting are removed, the receiving can be always executed in the best condition and the operation panel can be made simple.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an automatic switching device for the passband width of an intermediate frequency amplifier in an AM stereo receiver, which is suitable for use in a car stereo or the like that receives AM radio broadcasts. It is.

Conventional AM radio broadcast frequencies are every 9 KHz or 1 OKH2, and in order to avoid reception interference due to adjacent broadcasts, the channel plan is designed so that there are no adjacent broadcast stations within the same service area. However, due to the characteristics of broadcast radio waves that are affected by the ionosphere, reception interference due to adjacent channels outside the service area often occurs at night.
6 KHz (hereinafter referred to as narrowband IP) to avoid reception interference. However, in reception using a narrow band IF, the high range of audible frequencies is cut, so in the case of stereo reception, the stereo effect is of course significantly impaired. In order to avoid such inconvenience and obtain a stereo effect, the intermediate frequency amplifier should be used with a wide band (hereinafter referred to as
It is necessary to use a wideband IF with a passband width of 10KH2 or more. For this reason, conventional AM stereo receivers are equipped with a changeover switch to deal with conflicting IP bands: narrowband IP to deal with reception interference caused by broadcast waves from adjacent broadcasting stations, and wideband IF to obtain a good stereo effect. By manually operating the switch, the listener can select the intermediate frequency amplifier to be narrow band or wide band.

Problems to be Solved by the Invention As mentioned above, switching using the changeover switch is done manually regardless of the presence or absence of stereo broadcasting, so listeners sometimes forget to switch, or listeners have to judge whether it is stereo broadcast or monaural broadcast and then perform the switching operation. It is very inconvenient as it is very complicated. Also, adding more switches to a small space on the control panel of a car stereo, etc.
This poses an extremely inconvenient problem in that parts placement is difficult.

Means for Solving the Problem The present invention calculates the passband width of an intermediate frequency amplifier using information on stereo reception or monaural reception obtained from the output of a stereo indicator included in a stereo demodulator of an AM stereo receiver. , wideband when receiving stereo broadcasts,
The above-mentioned problems are solved by using a reception method that automatically switches to a narrow band during monaural broadcasting. Fig. 1 shows an overview of the automatic intermediate frequency bandwidth switching method of the present invention. An illustrative block diagram is shown.

In the figure, reference numeral 1 denotes an intermediate frequency amplifier, which includes a wide band intermediate frequency filter 2 and a narrow band intermediate frequency filter 3 inside.

The respective outputs of the two types of filters become inputs 4A and 4B of the intermediate frequency band switch 4. When the intermediate frequency band switching control input 4C is, for example, low level, the intermediate frequency band switching device 4 switches one input side ψ of the intermediate frequency band switching device 4 to one input side ψ of the intermediate frequency band switching device 4; The input side 4B is selected, and either a wideband intermediate frequency or a narrowband intermediate frequency is outputted at its output 4D.

-3=The stereo demodulator 5 demodulates the stereo composite symbol into left and right audio signals, and lights up the stereo indicator 6 when receiving a stereo signal. The output of the stereo indicator 6 becomes an intermediate frequency band switching control input 4C, which becomes a low level when receiving a stereo signal and a high level when a monaural signal is received, so that the intermediate frequency band width is automatically switched.

Embodiment FIG. 2 shows a specific example of a circuit for implementing the present invention. Each part will be explained below with reference to FIG. I is A consisting of IC-1
This is an intermediate frequency amplifier including an M tuner system, and the peripheral circuits of the IC-1 will be omitted.

As shown in the figure, a wide band intermediate frequency filter 2 and a narrow band intermediate frequency filter 3 connected in series are connected to pin A of the IC-1. Moreover, the wideband intermediate frequency filter 2 includes a wideband IPT2A and a wideband ceramic filter 2B.
Therefore, the narrowband intermediate frequency filter 3 is a narrowband IFT3A.
and a narrow band ceramic filter 3B.

Needless to say, both IFTs are constants that are optimal for the ceramic filter to be combined. Wideband IF
The secondary outputs of T2A and narrowband rFT3A are controlled to be turned on or off by transistors Q1 and Q2, which function as switches. When setting the wideband ■F, the transistor Q2 is turned on by the control signal of the intermediate frequency band switch 4, short-circuiting the secondary winding of the narrowband IFT 3A, and placing the narrowband IFT connected in series with the wideband IFT in an inoperable state. And conversely, when narrowband IP' is used, Q
Turn on l and short-circuit the secondary winding of broadband IFT2A,
Narrowband II? 'The broadband IFT in series with T is made inactive. The output of the wideband IFT is the input of the wideband ceramic filter, and the output of the narrowband IFT is the input of the narrowband 1
'F' are connected to the inputs of T respectively. The outputs of the two ceramic filters become inputs to the diodes DI and D2 of the intermediate frequency band switcher 4. That is, the output of the wideband ceramic filter 2B is connected to the cathode of the diode Di, and the output of the narrowband ceramic filter 3B is connected to the cathode of the diode D2. The diode DI is turned on by the control signal of the intermediate frequency band switcher 4 during wideband IF, and if R1 = R2 = R3, both ends of R3 will be approximately 1/1 of the circuit supply DC power supply voltage (10B). The voltage will be 2. Therefore, the diode D2 is reverse biased and turned off, and a broadband IP output can be obtained on the cathode side, which is the common terminal of the diodes D1 and D2. Conversely, when using narrowband IP, diode D2 is turned on,
The diode D1 is reverse biased, and the output of the narrow band IF can be obtained on the cathode side. By the above operation, a wideband IF or a narrowband IF is output as the output of the intermediate frequency band switcher 4, and this output is input to pin B of IC-1 and amplified by the IC-1, and on the other hand, pin C From IP
Obtain specific power. The output is input to pin D of IC-2 of the stereo demodulator 5.

Although not shown in Figure 2, the output of pin C of IC-1,
If the level is insufficient compared to the specified input level of IC-2, an amplifier may be inserted between the two. The operation of the intermediate frequency band switch 4 can be understood from the level diagram shown in FIG. The output of pin E of IC-2 acts on transistor Q3 as a control input signal for intermediate frequency band switch 4. During stereo reception, pin E of IC-2 becomes low level. Therefore, the transistor Q3 is turned on, and the collector of the transistor becomes high level (approximately +B). The collector of transistor Q3 and the transistor Q
The transistor Q4 is turned off by the diode D3 connected to the base of the transistor Q4, and the collector of the transistor Q4 becomes a low level (ground). The collector output of the transistor Q3 turns on the transistor Q2 and the intermediate frequency band switching diode DI, respectively, and the wide band IF is selected as described above. IC- when receiving monaural
Pin E of No. 2 becomes high level. Therefore, the collector of the transistor Q3 is at a low level, the transistor Q4 is turned on, and the collector of this transistor is at a high level.

The collector output of the transistor Q4 turns on the transistor Q1 and the diode D2, respectively, and the narrow band 1F is selected by the above-described operation. On the other hand, when receiving stereo
Pin E of C-2 is at a low level, which is the same as described above during stereo reception.

Effects Since the present invention is configured and operates as described above, there are no malfunctions or forgetting to switch, compared to receivers using conventional manual changeover switches.
It will always be possible to receive it in the best condition. In addition, since there is no need for a wideband/narrowband switching switch, it helps simplify the operation panel, allowing for effective use of the operation panel.
This can be said to be a very significant invention.

[Brief Description of the Drawings] Fig. 1 is a block diagram showing an overview of the present invention, Fig. 2 is a circuit diagram of an embodiment of the present invention, and Fig. 3 is a block diagram showing the operation of an intermediate frequency band switcher. Level diagram. ■ is an intermediate frequency amplifier, 2 is a wideband intermediate frequency filter, 2
A is wideband IFT, 2B is wideband ceramic filter,
3 is a narrowband intermediate frequency filter, 3A is a narrowband IF'T,
3B is a narrow band ceramic filter, 4 is an intermediate frequency band switcher, 4A and 4B are inputs, 4C is manual intermediate frequency band switching control, 4D is an output, 5 is a stereo demodulator, 6
is a stereo indicator. Patent application: Takara Seisakusho Co., Ltd.-11=

Claims (1)

[Claims] For equipment that can receive AM stereo broadcasts. stereo/mono included in broadcast radio waves. Intermediate frequency amplifier corresponding to the digital information signal A means to automatically switch the passband width of AM stereo receiver characterized by having Shinki.