JPH041535B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an FM/AM wave receiving antenna device for a vehicle.

Vehicle FM/AM wave receiving antenna devices, which are generally installed and used in vehicles such as automobiles, are equipped with a main antenna for receiving FM waves and AM waves and a sub-antenna for receiving FM waves. The main antenna and auxiliary antenna are switched and controlled to supply FM waves to the FM/AM radio receiver inside the vehicle.
On the other hand, when receiving AM, there is no need to switch the directivity of the antenna, so the antenna output of the main antenna is amplified and supplied to the FM/AM radio receiver.

However, such conventional vehicle FM/
The AM wave receiving antenna device has a plurality of antenna switching diodes connected to the output terminals of the main antenna and the sub antenna through capacitors, respectively.
Since the antenna output input to the FM/AM radio receiver is selectively turned on and off during FM reception, it is switched from the main antenna to the auxiliary antenna or from the auxiliary antenna to the main antenna, so the above diode remains on even during AM reception. . For this reason, there was a drawback in that the reception sensitivity of AM waves was significantly reduced due to the capacitive load effect of the antenna switching diode.

The present invention has been made to eliminate the above-mentioned drawbacks, and its purpose is to reduce the decrease in AM wave receiving sensitivity due to the capacitive load effect of the antenna switching diode, and to provide an AM wave with good receiving sensitivity during AM reception. An object of the present invention is to provide an FM/AM wave receiving antenna device for a vehicle that can supply FM/AM wave receiving antenna to an FM/AM radio receiver.

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

Figure 1 shows a vehicle FM/
FIG. 2 is a block diagram of an AM wave receiving antenna device. In the figure, A1 is a main antenna for receiving FM waves, A2 is a sub antenna for receiving FM waves,
These antennas A1 and A2 are mounted, for example, on the roof of a vehicle with a distance of 1/4 wavelength or more. Also,
The output terminals of the main antenna A1 and the auxiliary antenna A2 are connected to the input terminal of an antenna switching and AM wave branching circuit 2 provided in the diversity unit 1 via feeder lines F1 and F2, respectively. This antenna switching and AM wave branching circuit 2
The output terminal of is connected to the input terminal of an FM/AM radio receiver 3 installed in the vehicle, and the antenna outputs of the main antenna A1 and the auxiliary antenna A2 are connected to the antenna switching and AM wave branching circuit 2.
The configuration is such that the signal is input to the FM/AM radio receiver 3.

In addition, 4 in the figure extracts multipath noise from the FM wave input to the FM/AM radio receiver 3 during FM reception, detects the noise level, and the detected value is greater than a preset threshold. This is a multipath noise detection and antenna switching signal generation circuit that sends an antenna switching signal to the antenna switching and AM wave branching circuit 2 when Therefore, the antenna output input to the FM/AM radio receiver 3 is transmitted from the main antenna A1 to the sub antenna A2 or the sub antenna A2.
The antenna is now replaced by the main antenna A1.

FIG. 2 is a circuit diagram showing the configuration of the antenna switching and AM wave branching circuit 2.
0 are antenna switching diodes D1 and D2 connected to the output terminals of the main antenna A1 and the auxiliary antenna A2 via capacitors C1 and C2, respectively.
and drive transistors Q1 and Q2 that selectively turn on and off these diodes D1 and D2.

The cathodes of the diodes D1 and D2 are connected to the power supply terminal B via resistors R2 and R3, respectively, and the anodes of the diodes D1 and D2 are connected to the input terminal T3 of the FM/AM radio receiver 3 via a capacitor C3. and is connected to a fixed contact S1 of the changeover switch SW via a resistor R1. The movable contact portion of the changeover switch SW is connected to a power supply terminal B, and a bias voltage is applied from the power supply terminal B to the diodes D1 and D2 during FM reception.

On the other hand, terminals T1 and T2 are connected to the bases of the transistors Q1 and Q2, respectively.
An antenna switching signal is applied to these terminals T1 and T2 from the multipath noise detection and antenna switching signal generation circuit 4 described above. For example, when an antenna switching signal is applied to terminal T1, transistor Q1 is turned on. I'm starting to do that. The collectors of the transistors Q1 and Q2 are connected to the cathodes of diodes D1 and D2 via coils L1 and L2, respectively, and the emitters are grounded.

Further, the output terminal of the main antenna A1 is connected to an FET (field effect transistor) via a coil L3 and a capacitor C4 that constitute the AM wave branching circuit 20.
Connected to the gate of Q3. This FETQ3 is an AM branched from the antenna output of the main antenna A1 by the coil L3 and capacitor C4.
FETQ is used to amplify waves to a predetermined level.
The source and gate of No. 3 are each connected to a ground potential point via a resistor.

In addition, the drain of FETQ3 is connected to the fixed contact S2 of the changeover switch SW via a resistor R5, and is connected to the transistor Q via a capacitor C5.
Connected to the base of 4. The emitter of this transistor Q4 is connected to the ground potential point via a resistor R8, and is also connected to the input terminal T3 of the FM/AM radio receiver 3 via a capacitor C6 and a coil L4, and is amplified by the FET Q3. The AM wave is connected to capacitor C6 and coil L4.
The signal is configured to be input to the FM/AM radio receiver 3 through the FM/AM radio receiver 3.

Note that the collector of the transistor Q4 is connected to the fixed contact S2 of the changeover switch SW. Also, the base of transistor Q4 and capacitor C5
An intermediate connection point P2 of a resistor R6 and a resistor R7 connected in series is provided between the fixed contact S2 of the changeover switch SW and the ground potential point.

In such a configuration, when the movable contact of the changeover switch SW is switched from the fixed contact S2 side to the fixed contact S1 side, the diode D1,
A bias voltage is applied to D2. At this time, when an antenna switching signal is applied from the multipath noise detection and antenna switching signal generation circuit 4 to the terminal T1, a current flows from the collector to the emitter of the transistor Q1. As a result, diode D1 turns on, and the antenna output of main antenna A1 is connected to capacitor C1, diode D1, and capacitor C.
3 and is input to the FM/AM radio receiver 3.

At this time, if the multipath noise level of the FM wave input to the FM/AM radio receiver 3 is higher than the threshold value, an antenna switching signal is sent from the multipath noise detection and antenna switching signal generation circuit 4 to the terminal T2. is given. This turns on the transistor Q2, and the antenna output of the auxiliary antenna A2 is input to the FM/AM radio receiver 3 via the capacitor C2, diode D2, and capacitor C3.

On the other hand, when the movable contact of the changeover switch SW switches from the fixed contact S1 side to the fixed contact S2 side as shown in FIG. A reverse bias voltage is applied through R3. As a result, the antenna output of main antenna A1 is
It flows into the AM wave branching circuit 20, and the AM wave is extracted from the antenna output of the main antenna A1 by the coil L3 and the capacitor C4. and extracted
After the AM wave is amplified to a predetermined level by FETQ3, it is input to FM/AM radio receiver 3 via transistor Q4, capacitor C6, and coil L4.

In this way, the main antenna A1 and the sub antenna A2
Each diode D1, D2 connected to the output terminal of
On the other hand, when receiving AM, a reverse bias voltage is applied,
The antenna output of the main antenna A1 is sent to the AM wave demultiplexing circuit 20 to demultiplex the AM wave, and the demultiplexed AM wave is supplied to the FM/AM radio receiver 3. It can reduce the decrease in AM wave reception sensitivity due to load effect, and
AM waves with good reception sensitivity can be supplied to the FM/AM radio receiver 3 during reception.

As explained above, the vehicle FM/AM of the present invention
The wave receiving antenna device is an FM installed on the vehicle.
A main antenna for receiving waves and AM waves, a sub-antenna for receiving FM waves mounted on the vehicle at a distance of 1/4 wavelength or more from the main antenna, and a capacitor at the output terminal of each of these main antennas and sub-antennas. a plurality of antenna switching diodes connected through the diodes; voltage switching means for applying a bypass voltage to each of these diodes during FM reception and a reverse bias voltage during AM reception;
Detects the multipath noise level of FM waves input to the FM/AM radio receiver in the vehicle during reception, and selectively turns on and off the antenna switching diode when the detected value is greater than a preset threshold. means for switching the antenna output input to the FM/AM radio receiver from the main antenna to the sub antenna or from the sub antenna to the main antenna, and branching AM waves included in the antenna output of the main antenna when receiving AM. and said FM/
It is equipped with AM wave demultiplexing means for supplying AM waves to an AM radio receiver.

Therefore, it is possible to reduce the decrease in AM wave reception sensitivity due to the capacitive load effect of the antenna switching diode, and to receive AM waves with good reception sensitivity during AM reception.
Can be supplied to FM/AM radio receivers.

[Brief explanation of drawings]

1 and 2 show one embodiment of the present invention, FIG. 1 is a block diagram of an FM/AM wave receiving antenna device for a vehicle, and FIG. 2 shows an antenna switching and
FIG. 2 is a circuit diagram showing the configuration of an AM wave branching circuit. 1... Diversity unit, 2... Antenna switching and AM wave branching circuit, 3... FM/AM radio receiver, 4... Multipath noise detection and antenna switching signal generation circuit, Al... Main antenna,
A2...Auxiliary antenna, D1, D2...Antenna switching diode.

Claims (1)

[Claims] 1. A main antenna for receiving FM waves and AM waves attached to a vehicle, a sub-antenna for receiving FM waves attached to the vehicle at a distance of 1/4 wavelength or more from this main antenna, and these main antennas and sub-antennas. a plurality of antenna switching diodes each connected to the output terminal of the antenna via a capacitor; voltage switching means for applying a bias voltage to each of these diodes during FM reception and a reverse bias voltage during AM reception; Detects multipath noise noise of FM waves input to the FM/AM radio receiver in the vehicle during reception, and selectively turns on and off the antenna switching diode when the detected value is greater than a preset threshold. and said above
means for switching the antenna output input to the FM/AM radio receiver from the main antenna to the auxiliary antenna or from the auxiliary antenna to the main antenna;
An FM/AM wave receiving antenna device for a vehicle, comprising an AM wave branching means for branching AM waves and supplying the AM waves to the FM/AM radio receiver.