JPH0345569B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an antenna amplifier for an automobile receiving device that amplifies a received wave from a receiving antenna attached to the automobile and supplies the amplified wave to the receiving device.

In recent years, a heating wire has been attached to the rear windshield of a car, and when the rear window fogs up, electric current is passed through the hot wire to generate heat, raising the temperature of the rear windshield and eliminating fogging. , the above-mentioned hot wire is being used as an antenna for an automotive receiver.

Conventionally, as shown in FIG. 1, this type of automotive receiver described in Japanese Patent Publication No. 56-2444, for example, has been used in a vehicle (not shown).
A plurality of hot wires 2, . , 2 is used as a heating means for the windshield 1 of 2 and as a receiving antenna for AM broadcasting, and an FM antenna wire 5 for receiving FM broadcasting is attached to the top of the heating wires 2, ..., 2, and the heating wire 2 on the top row and the above FM antenna The wire 5 is connected to the wire 7 with a stub 6 formed in the middle in order to prevent high frequency interference between the hot wires 2,..., 2 as an AM receiving antenna and the FM antenna wire 5.
The electrode part 8 drawn out from the FM antenna wire 5 and the receiving device 9 were connected by a wire 10.

Between the power supply section 3 of the hot wires 2, ..., 2 and the defogger switch 11 that turns on and off the power supply from the battery B to the hot wires 2, ..., 2, and between the other power supply section 4 and the ground. The above hot wire 2,...,
In order to prevent the high frequency current received by the antenna wire 2 and the FM antenna wire 5 from leaking to the battery B and the ground side, coils L ₁ and L ₂ having large impedance against the above high frequency current are connected, respectively. The high frequency current leaked to the battery B side is bypassed to the ground by the capacitor C adjacent to the coil _L1 and the ground.

In the above-mentioned automotive receiver, the hot wires 2,...,2 and the FM antenna wire 5 are all attached to the window glass 1, so the hot wires 2,...,2 and the FM antenna wire 5 are connected to the antenna. Therefore, a broadband antenna amplifier 12 was inserted immediately after the electrode part 8 drawn out from the FM antenna wire 5 in FIG.
..., 2 or the FM antenna line 5 is amplified and then supplied to the receiving device 9.

By the way, when the wideband antenna amplifier 12 as described above is inserted immediately after the electrode section 8, the level of the signal input to the receiving device 9 becomes high over the entire bandwidth of the antenna amplifier 12, and the car becomes difficult to broadcast. When driving in an area with strong radio field strength,
There is a problem in that the level of the signal input to the receiving device 9 exceeds a specified value, the received wave is distorted inside the receiving device 9, and the sound output from the speaker 13 of the receiving device 9 is distorted.

For example, the electric field strength of broadcast waves with frequencies f ₁ , f ₂ , f ₃ , and f ₄ at a certain point has the magnitude as shown in Figure 2, and the electric field strength of broadcast waves with frequency f ₂ exceeds 100dB, the frequency f ₂ at the above point
When the broadcast wave is received, the speaker 1 of the receiving device 9
3 outputs distorted audio.

In order to prevent the occurrence of such distortion, a high frequency attenuator has been proposed in which the input level of the receiver is adjusted by inserting and removing a fixed resistor attenuator (see, for example, Japanese Utility Model Application Publication No. 176621/1983). .

The above-mentioned high-frequency attenuator is a high-frequency attenuator that adjusts the input level by inserting and removing a fixed resistance attenuator. It is also applied to the level detection rectifier circuit via a changeover switch that allows the insertion and removal of the level detection amplifier, and the output of the level detection rectification circuit is used to preset the level value before the input signal reaches the saturation level of the receiver. When the value exceeds the value, the control circuit that controls the attenuator changeover switch and the level detection amplifier changeover switch is activated, and automatically switches both of the changeover switches to switch the fixed resistance attenuator and the level detection amplifier. The circuit is configured so that it can be inserted automatically.

By the way, the above-mentioned device does not determine the electric field strength of the received radio waves to be heard and insert/remove the fixed resistance attenuator from the antenna input terminal. Therefore, in the above device, the electric field strength at the receiving point is 100 dB.
When trying to receive broadcast waves smaller than
It is necessary for the receiver to amplify the signal received by the antenna to an appropriate level and input it to the receiver, but at this time, if the field strength of the broadcast radio waves is not determined and the
When the field strength of another broadcast radio wave with a field strength exceeding 100 dB is determined, the fixed resistance attenuator remains inserted in the antenna input terminal, and the signal at the appropriate level is not input to the receiver. It was hot.

Also, as mentioned above, when the level of the received wave is high, if a fixed resistance attenuator is inserted between the antenna input terminal and the receiver, the receiver's input when looking from the antenna input terminal to the receiver side There was also the problem that the impedance changed and the reception performance of the receiver deteriorated.

Furthermore, in order to prevent the input level of the level detection amplifier from decreasing due to the insertion of the fixed resistance attenuator as described above, it is necessary to add another level detection amplifier when inserting the fixed resistance attenuator. It is necessary to insert the two levels at the same time, and two sets of level detection amplifiers are required, resulting in a complicated circuit configuration.

SUMMARY OF THE INVENTION An object of the present invention is to provide an antenna amplifier for a car receiving device that is simple in structure and has excellent functionality, and can receive broadcasts without distortion or noise without being affected by the field strength of the received radio waves at the receiving point. It is said that

For this reason, the present invention provides an antenna amplifier that amplifies the received wave of a receiving antenna installed on a car and supplies it to a receiving device mounted on the vehicle, and the antenna amplifier is provided with a tuning signal from the receiving device. Gain reduction that is activated by a signal from a received wave level detection circuit that detects the level of the received wave at the tuned frequency between the receiving antenna and the antenna amplifier, and lowers the gain of the antenna amplifier when the level of the received wave at the tuned frequency is high. It is characterized by the fact that the circuit is connected.

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 3 shows an embodiment in which the present invention is applied to the automotive receiver shown in FIG.

Note that in FIG. 3, parts corresponding to those in FIG. 1 are indicated with corresponding symbols, and redundant explanations will be omitted. In FIG. 3, reference numeral 21 denotes an antenna amplifier 2 which amplifies the received waves received by the hot wires 2,..., 2 or the FM antenna wire 5 attached to the window glass 1 and supplies the amplified waves to the receiving device 9.
2 is a gain reduction circuit.

The gain reduction circuit 22 includes a controller circuit 24 that turns on the relay switch 23 when the level of the received wave of the tuning frequency of the received radio wave is high, and a bypass capacitor _C1 for impedance matching. Then, the gain reduction circuit 22 controls the heating wires 2,..., 2 by the controller circuit 24.
Alternatively, the level of the received wave received by the FM antenna line 5 is compared with a reference level described later, and when the level of the received wave is higher than the reference level, the relay switch 23 is turned on and the reception signal is input to the antenna amplifier 21. wave bypass capacitor
The signal is bypassed to the receiving device 9 through _C1 .

The control circuit 24 includes a variable narrowband filter circuit 25 and an electric field strength detection circuit 26, as shown in FIG.

The variable narrowband filter circuit 25 has a frequency characteristic with a narrow bandwidth, and the center frequency of this narrow bandwidth is determined according to the tuning frequency of the receiving device 9 by a tuning signal supplied from the receiving device 9 through the wire 29. Things are starting to change.

The output of the variable narrowband filter circuit 25 is input to a field strength detection circuit 26 for amplification and detection, and a DC voltage having a value corresponding to the field strength of the received radio wave is obtained from the field strength detection circuit 26. .

The output of the electric field strength detection circuit 26 is output from the comparison circuit 2.
7 and is compared with a reference voltage in the comparison circuit 27.

The above-mentioned reference voltage is a command signal that is output from the comparison circuit 27 to command the activation of a relay (not shown) when the field strength of the received radio wave to which the receiving device 9 is tuned exceeds, for example, 100 dB. It is set to a value like this.

The relay drive circuit 28 energizes the relay in response to the command signal inputted from the comparison circuit 27 and turns on the contact 23 thereof.

The variable narrow band filter circuit 25 and the electric field strength detection circuit 2 of the controller circuit 24 described above
6, a circuit as shown in FIG. 5 can be used.

A variable narrow band filter circuit 25, a high frequency transformer 30 having coils L ₃ and L ₄ , a variable capacitance diode D ₁ , a capacitor C ₂ and an amplifier 3 shown in FIG.
Consists of 1.

The coil L ₃ is connected between the electrode part 8 attached to the window glass 1 and the ground, while
One end of the coil _L4 is connected to the cathode of the variable capacitance diode _D1 , and the other end of the coil _L4 is connected to the ground together with the anode of the variable capacitance diode _D1 .

Cathode and coil of the above variable capacitance diode _D1
A tuning voltage whose magnitude changes depending on the tuning frequency is applied as a tuning signal from the receiving device 9 (see FIG. 3) to the connection point 32 with one end of _L4 .

The above coil L ₄ and variable capacitance diode D ₁ are LC whose resonant frequency changes depending on the above tuning voltage.
A resonant circuit is constructed, and its output is input to the amplifier 31 from the connection point 32 through the capacitor _C2 .

Note that the above-mentioned tuning voltage is, when the receiving device 9 is of a well-known frequency synthesizer type,
The tuning voltage inside the receiving device 9 can be used as is.

On the other hand, the electric field strength detection circuit 26 includes an amplification detection circuit 33, a resistor _R3 and a capacitor that constitute a smoothing circuit.
C ₃ and a DC amplifier 34.

The electric field strength detection circuit 26 amplifies and detects the output of the amplifier 31 of the variable narrowband filter circuit 25 with an amplification/detection circuit 33, converts it into a DC voltage with a smoothing circuit consisting of a resistor R ₃ and a capacitor C ₃ , and converts it into a DC voltage. The DC voltage is amplified by a DC amplifier 34.

The output of the DC amplifier 34 changes depending on the field strength of the received radio waves to which the receiving device 9 is tuned, and is input to the comparison circuit 27 and compared with a reference voltage.

Next, the operation of the antenna amplifier of the automotive receiver whose configuration has been explained above will be explained.

Assume now that the receiving device 9 is tuned to a received radio wave of frequency _f2 , for example, whose electric field intensity is shown in FIG. At this time, the tuning signal of the frequency f2 is input from the receiving device 9 to the variable narrowband filter circuit 25 of the controller circuit 24, and the variable narrowband filter circuit ₂₅ is tuned to the frequency _f2 . Thereby, the received signal of the frequency f ₂ received by the receiving device 9 is also input to the field strength detection circuit 26 from the variable narrow band filter circuit 25,
The electric field strength of the received radio wave at the frequency _f2 is detected.

By the way, since the electric field strength of the received radio wave at frequency _f2 exceeds 100 dB, the controller circuit 24
The comparison circuit 27 outputs a command signal for energizing the relay, and the relay drive circuit 28 energizes the relay to turn on the relay contact 23.

Therefore, the received signal of the received radio wave of frequency f ₂ received by the hot wires 2,..., 2 or the FM antenna wire 5 is directly transmitted to the receiving device through the bypass capacitor C ₁ without being amplified by the antenna amplifier 21. 9, distortion of the received waves does not occur, and audio distortion of the receiving device due to the strong electric field can be eliminated.

On the other hand, when the receiving device 9 is tuned to the received radio wave of frequency f ₁ as shown in FIG. 2, the variable narrow band filter circuit 25 is tuned to the received radio wave of frequency f ₁ . Thereby, the electric field strength of the received radio wave of the frequency f ₁ being received by the receiving device 9 is detected by the electric field strength detection circuit 26 in the same manner as described above. Since the electric field strength of the received radio wave with the frequency f ₁ is smaller than 100 dB, the comparison circuit 27 of the controller circuit 24 outputs a command signal instructing to de-energize the relay, and the relay drive circuit 28 de-energizes the relay. This will turn off the relay contact 23.

For this reason, the received signal of the received radio wave of frequency f ₁ received by the hot wires 2,..., 2 or the FM antenna wire 5 is amplified by the antenna amplifier 21, and then
The signal is then given to the receiving device 9, and even a received signal due to a received radio wave with a small electric field strength is amplified to a level that allows the receiving device 9 to receive it normally.

Therefore, even when receiving radio waves of the frequency f ₁ , it is possible to obtain sound without noise.

In this way, the electric field strength of the received radio wave having the tuned frequency to which the receiving device 9 (its tuning circuit) is tuned is determined, and the level of the signal input to the receiving device 9 is always appropriate. Since the receiving device 9 is controlled as follows, it is possible to obtain sound without distortion or noise.

In the above embodiment, instead of the comparator circuit 27 and relay drive circuit 28 of the controller circuit 24, it consists of a transistor Q and resistors R ₄ and R ₅ as shown in FIG. An emitter follower circuit 35 is provided which uses the power supply voltage, and a gain control signal obtained by impedance-converting the output of the field strength detection circuit ₂₆ is applied from the emitter of the transistor Q of the emitter follower circuit 35 to the antenna amplifier 21 through the diode D2. The gain of the amplifier 21 may be controlled by the gain control signal, and the gain of the antenna amplifier 21 may be controlled to become smaller as the electric field strength becomes stronger.

By doing so, the gain of the antenna amplifier 21 is continuously controlled according to the field strength of the received radio waves, and a more preferable result can be obtained.

Note that the antenna amplifier of the present invention can be applied to an antenna attached to a windshield or a pole antenna in addition to the antenna of the above embodiment.

As is clear from the detailed explanation above, according to the present invention, the field strength of the received radio waves to be heard is detected and determined, and the gain of the antenna amplifier is controlled based on this result. The gain is controlled based on the field strength of the received radio wave that the receiving device is tuned to.
A signal of an appropriate level is always input to the receiving device, and there is no distortion even if the field strength of the received radio waves is large, and there is no noise etc. even if the field strength of the received radio waves is small. It is possible to obtain sound without generation.

Furthermore, according to the present invention, there is no need to connect an attenuator such as a resistor between the antenna and the antenna amplifier, and since the gain of the antenna amplifier is controlled according to the electric field strength of the received wave, the input impedance of the antenna amplifier There is no change in the antenna amplifier, and the antenna amplifier can always be used at its full potential.

Furthermore, according to the present invention, since an attenuator such as a resistor is not connected between the antenna and the antenna amplifier, the signal input to the antenna amplifier directly reflects the field strength of the received radio waves. The amplification gain of the radio wave changes after the antenna amplifier, making it easier to detect the level of the received wave.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of a conventional automobile receiver that uses a hot wire attached to the windshield of the rear window as an antenna, and Figure 2 is an illustration of the relationship between the electric field strength of received waves and the occurrence of distortion. 3 is an explanatory diagram of an automotive receiver using the antenna amplifier according to the present invention, FIG. 4 is a block diagram of a controller circuit, and FIG. 5 is a diagram of a variable narrowband filter circuit and a field strength detection circuit. A specific circuit diagram, FIG. 6, is an explanatory diagram of a modification of FIG. 3. 1...window glass, 2...heat ray, 5...
FM antenna line, 9... Receiving device, 21... Antenna amplifier, 22... Gain reduction circuit, 23... Relay switch, 24... Controller circuit, 25
... variable narrow band filter circuit, 26 ... field strength detection circuit, 27 ... comparison circuit, 28 ... relay drive circuit, 35 ... emitter follower circuit.

Claims (1)

[Scope of Claims] 1. An antenna amplifier that amplifies a received wave from a receiving antenna installed on a car and supplies it to an on-vehicle receiving device, the antenna amplifier having a tuning signal input from the receiving device. Gain reduction that is activated by a signal from a received wave level detection circuit that detects the level of the received wave at the tuned frequency between the receiving antenna and the antenna amplifier, and lowers the gain of the antenna amplifier when the level of the received wave at the tuned frequency is high. An antenna amplifier for an automobile receiving device, characterized in that a circuit is connected to the antenna amplifier. 2. In the antenna amplifier for a car receiver according to claim 1, the gain reduction circuit includes a switch element that shorts between the input and output of the antenna amplifier, and a switch element that turns on the switch element when the level of the received wave is higher than a set level. An antenna amplifier for an automobile receiving device, comprising an electric field measuring circuit.