JPS631483Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a tuner for receiving broadcast radio waves, and particularly to noise reduction.

Generally, audio equipment includes a tuner section that receives and demodulates radio waves such as AM and FM, a preamplifier section,
The main amplifier section or the integrated amplifier section, which is a combination of a preamplifier and a main amplifier, are divided and housed in separate housings. When transmitting a signal between each housing, a shielded cable is used to connect the housings, that is, between the ground potentials of the housings, using the shielded cable.

However, when transmitting and receiving signals between a plurality of electronic devices in this way, there is a problem in that noise is generated due to the current flowing due to the difference in ground potential between the devices. In particular, when receiving AM radio waves using a tuner for receiving broadcast radio waves, there was a problem in that the radio waves were easily affected by noise and the sound quality deteriorated significantly.

On the other hand, in professional audio equipment, for example, the first
As shown in the figure, an output signal from a first device 1 is inputted via a cable 3 to an input transformer 2a of a second device 2 via an output transformer 1a. In this case, the secondary side of the output transformer 1a and the primary side of the input transformer 2a are floated relative to the casings of the devices 1 and 2, that is, their respective ground potentials, to prevent noise due to the potential difference. . However, such a device requires an extremely expensive transformer in order to transmit signals with high fidelity, and the tuner section itself cannot cope with noise that enters through its ground potential.

In other words, an AM/FM tuner that is generally used as an audio device, that is, a tuner for receiving broadcast radio waves, uses a dedicated external antenna for receiving FM radio waves, and a built-in loop antenna or a coil in a rod-shaped ferrite core for receiving AM radio waves. A wrapped bar antenna is used.

Figures 2 and 3 show the antenna circuit of the FM receiving section of such a tuner. In the one shown in Figure 2, the primary side of the antenna coil 4 is wound to an impedance of 300Ω, and the midpoint is connected to the ground potential. (for example, Chuyuna chassis), and connect both ends to 300
It is connected to terminal 5 for parallel feeder of Ω. One end of the primary coil 4a is connected to a terminal 6 for a 75Ω coaxial cable. Further, a variable capacitor 7 is connected to the secondary coil 4b to form a tuned circuit.

In the case shown in Fig. 3, a 300Ω parallel feeder terminal 5 is connected to a tap derived from a 75Ω impedance point of the antenna coil 4 via a balun 8 that converts the impedance to 4:1, and a coaxial cable is connected to this tap. Terminal 6 for this purpose is also connected.

Therefore, in both of the devices shown in FIGS. 2 and 3, the voltage induced in the external FM antenna is connected to the ground potential of the tuner via the primary side 4a of the antenna coil 4 or the balun 8. That will happen. However, since the impedance of the coil, balun 8, etc. on the primary side 4a is low for the low frequency of AM broadcasting, the above-mentioned induced voltage flows to the ground potential of the tuner with almost no attenuation, and is generated when receiving AM radio waves. This causes noise.

The present invention was developed in view of the above circumstances, and the purpose is to provide a tuner for receiving broadcast waves that can prevent noise especially when receiving AM radio waves and thereby perform reception with high fidelity. That is. An embodiment of the present invention is shown in Figures 4 to 6 below.
This will be explained in detail with reference to the drawings. Figure 4 shows the antenna circuit of the FM receiver.Antenna coil 1
The primary side of 1 is wound with an impedance of 300Ω, and both ends are connected to a 300Ω parallel feeder terminal 12. Further, the center tap and one end of this primary coil are connected to a terminal 13 for a 75Ω coaxial cable. That is, this primary coil is in a floating state from the ground potential of the tuner. The secondary side of this antenna coil 11 is connected to the primary side of the tuning coil 14, and one side is connected to the ground potential of the tuner. A variable capacitor 15 is connected in parallel to the secondary side of this tuning coil 14, one end of which is connected to the ground potential of the tuner, and a tap is derived from an appropriate position and applied to a high frequency amplification stage (not shown). . In this way, the voltage induced in the external FM antenna connected to the terminal 12 or 13 will be floated from the tuner's ground potential and will not become a noise source.

FIG. 5 shows the antenna circuit of the AM receiving section, in which the primary side of the tuning coil 16 is connected to, for example, a loop antenna 18 via the terminal 17, and this primary coil is connected to the ground potential of the tuner. is in a floating state. A variable capacitor 19 is connected in parallel to the secondary side of the tuning coil 16, and one end thereof is connected to the ground potential of the tuner, and a tap is derived from an appropriate position and applied to a high frequency amplification stage (not shown). There is. In this way, it is connected to the terminal 17. For example, since the loop antenna is floated from the ground potential of the tuner, it is possible to prevent noise components from flowing in from this ground potential.

Furthermore, FIG. 6 is a diagram showing the output terminals of the tuner for demodulating signals of FM or AM broadcasting, and in the figure, 20 is the output terminal of the right channel, and 21 is the output terminal of the left channel. Then, the common potential side of this output terminal, that is, the side that is connected to the ground potential of the integrated amplifier when connected to the integrated amplifier via a connection cable (not shown), is connected to the left and right channels in common, and the Connected to the tuner's ground potential. Note that this reactance 22 may be a coil having sufficient impedance to block signals at the frequency of AM radio waves, for example. In this way, the space charge induced by the cable for connecting the tuner and the integrated amplifier, the speaker cable, etc. connected to the output side of the integrated amplifier, and entering through the ground potential of the integrated amplifier can be blocked. Therefore, it is possible to prevent deterioration of sound quality such as generation of noise due to this.

Note that the above output terminals 20 and 21 have been described as output terminals for demodulating signals of received radio waves, but they are common to those connected to the ground electron of external equipment such as FM multipath observation output terminals and FM disk drive output terminals. The potential side is grounded to the chassis of the tuner via an appropriate reactance and floated at high frequency.

By floating the FM antenna, AM antenna, and signal output terminal with respect to the ground potential of the tuner, noise components that circulate through the ground potential are blocked, thereby preventing deterioration of sound quality and increasing the You can receive AM broadcast waves with high quality.

It should be noted that the present invention is not limited to the above-mentioned embodiment. For example, as shown in FIG. may be connected to ground potential.

It is also desirable to short-circuit this reactor 22 when receiving FM broadcasts to improve the slew rate, so for example, as shown in FIG. 8, the collector and emitter of a transistor 23 are connected in parallel, and a switch 24 is connected to its base. When selecting FM, the bias power supply 25 may be connected to conduct and short-circuit. Further, as shown in FIG. 9, a switch 26 which is short-circuited when FM is selected may be connected in parallel to the reactor 22. Furthermore, as shown in Fig. 10, when FM is selected, it is connected to the reactor 22,
A switch 27 may be provided which is directly connected to the ground potential of the tuner when AM is selected.

As detailed above, this invention is an FM antenna,
The common signal output terminal for the AM antenna and external equipment is floated with respect to the tuner's ground potential, which prevents noise components from circulating through the ground potential, thereby allowing AM broadcasts to be received with good sound quality. A tuner for receiving broadcast radio waves can be provided.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an example of the connection between commercial equipment, Figs. 2 and 3 are diagrams showing different examples of the antenna circuit of a conventional FM receiving section, and Figs. Figure 4 shows the antenna circuit of the FM receiver, Figure 5 shows the antenna circuit of the AM receiver, Figure 6 shows the connection terminal for external equipment, and Figures 7 to 10 show an embodiment of the present invention. FIG. 6 is a diagram showing connection terminals of other embodiments of the present invention; 11...Antenna coil, 12, 13, 17...
... terminal (for antenna), 14, 16 ... tuning coil, 15, 19 ... variable capacitance, 20, 21 ... output terminal, 22 ... reactance.

Claims (1)

[Scope of utility model registration request] In a tuner for receiving broadcast radio waves that receives FM radio waves and AM radio waves, an antenna coil of an FM receiving section whose primary side connected to the FM antenna is floated with respect to the ground potential of the tuner, and an antenna for AM. The primary side connected to the tuner is floating with respect to the ground potential of the tuner.
It is inserted between the antenna coil of the AM receiving section, the common potential side connected to the ground potential of the integrated amplifier of the signal output terminal, and the ground potential of the tuner.
A tuner for receiving broadcast radio waves, which is equipped with a reactance that blocks AM radio frequency signals.