JPH057789Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a receiver for a vehicle, and is particularly suitable for use in an antenna whose gain is significantly reduced due to ground stray capacitance.

[Summary of the idea]

The resonant coil has a core whose magnetic permeability changes depending on the frequency, in parallel with the ground stray capacitance of the antenna when looking from the input end of the tuner to the antenna side, and the inductance decreases as the reception frequency increases. This is an automotive receiver that uses at least one coil to compensate for signal loss due to stray capacitance over a wide band.

[Conventional technology]

Anti-fog heater conductors are attached to automobile window glasses (particularly rear window glasses) by baking or embedding. It is well known to use this heater conductor as part of an antenna or antenna element, for example for the AM broadcast band.

FIG. 9 is a conductor pattern diagram of such a windowpane antenna, in which a large number of heater wires 2 are attached to the anti-fog area of the rear windowpane 1, and a power feeding line connected to one end of the heater wires 2 divided into two groups, upper and lower, is shown in FIG. The configuration is such that power is fed back through the busbars 3 and 4 and via the relay busbar 5 at the other end. In order to use this heater wire 2 as a receiving antenna for AM broadcasting, a feed point 6 is provided on the relay bus 5.
A feeder 7 such as a coaxial line is connected to the receiver, and the received signal is led out to the tuner via a DC cut capacitor 8. The heating current is passed through the feeder lines 12 and 13 through the coils 11a and 11b which are magnetically coupled to each other.
is passed through to the power supply buses 3 and 4. Main power +B
The chiyoke coil 11a connected to the ground point and the chiyoke coil 11b connected to the ground point are negatively coupled,
The magnetic fluxes caused by the respective heating currents cancel each other out within the core, allowing the small volume core to operate in a non-saturated state. For receiving high frequency waves, the chiyoke coils 11a, 1
1b exhibits high impedance, and the received signal induced in the heater wire 2 does not escape to a low impedance power source or ground, thereby increasing power reception efficiency. Note that a decoupling capacitor 14 is connected to the line connected to the main power supply +B to prevent power supply noise from being added to the received signal.

FIG. 10 is an equivalent circuit of the antenna in FIG. 9, where e _p is the induced electromotive force of the heater wire 2, C ₁ is the effective capacitance of the antenna, C ₂ is the reactive capacitance of the antenna, C ₃ is the feed line 12, 13 and the feeder cable 7, C _c is the capacitance of the capacitor 8, R is the internal resistance of the antenna, and L _x is the inductance of the heater wire 2 and the chain coils 11a and 11b.

[The problem that the idea aims to solve]

When receiving AM broadcasting through the heater wire 2, the magnitude of the induced electromotive force e _p depends on the size of the rear window glass 1, and if the area of the window glass is small, the induced electromotive force e _p is small.

On the other hand, the reactive capacitance in the equivalent circuit of Figure 10
Even if the window glass area becomes smaller, C ₂ and C ₃ do not decrease proportionally. For this reason, if the window glass area is small, the signal loss due to reactive capacitances C ₂ and C ₃ will be relatively large, making it difficult to receive AM broadcasts well if a glass antenna with a small reception area is used. .

It is also possible to compensate for signal loss by installing a resonant coil in parallel with the stray capacitance (reactive capacitance), but since normal coils have their own resonant frequency, it is difficult to compensate for signal loss over a wide band. In this case, the circuit becomes complicated because a plurality of resonant coils are provided and these resonant coils are switched as appropriate.

In view of the above-mentioned problems, it is an object of the present invention to compensate for the decrease in gain due to reactive capacitance over a wide band with a simple configuration, thereby increasing reception sensitivity over a wide band.

[Means for Solving the Problems] The automotive receiver of the present invention is an automotive receiver in which a resonant coil is provided in parallel with the ground stray capacitance C _f of the antenna when looking at the antenna side from the input end 19a of the tuner 19. In the receiving device, at least one resonant coil _L3 is used as the resonant coil, which has a core whose permittivity changes depending on the frequency, and whose inductance decreases as the receiving frequency increases.

[Effect]

The ground impedance of the antenna seen from the tuner 19 increases in the receiving band due to parallel resonance, and signal loss due to the ground stray capacitance C _f is reduced. The resonant coil _L3 has a core whose magnetic permeability changes depending on the frequency in the reception band, and the inductance decreases as the reception frequency increases. That is, as the receiving frequency increases, the resonant frequency also increases.
Therefore, the bandwidth of the parallel resonance is widened, and wideband reception characteristics can be obtained.

〔Example〕

FIG. 1 is a wiring diagram of an automobile rear window glass antenna to which the present invention is applied, and FIG. 2 is a circuit diagram of a matching circuit showing an embodiment of the present invention. Note that the conductor pattern of the rear window glass 1 and the heating current feeding circuit are the same as those shown in FIG. 9. In the embodiment, the received signal of the heater wire 2 taken out from the feed point 6 is supplied to the matching circuit 20, and the output of the matching circuit 20 is supplied to the input end 19a of the tuner 19 via the 3-4 m feeder cable 7. are doing.

As shown in FIG. 2, a capacitor C _c and a coil L ₁ are connected in series between the input end 20 a and the output end 20 b of the matching circuit 20 . Also, the output side of coil L ₁ is connected to coil L ₂ and coil L _3.
grounded in series circuit.

Capacitor C _c is a coupling capacitor (capacitance is, for example, 1000 pF) for extracting the received power induced in heater wire 2, and the received signal with the DC component cut by this capacitor C _c is transferred to coil L ₁ . Given. The coil L ₁ is provided to improve reception sensitivity in the high frequency band of the AM broadcast band, and the coil L ₁ and the reactive capacitance C _f form a low-pass filter to be described later. Note that the reactive capacitance C _f between the output end 20b and the ground represents the ground stray capacitance of the feeder cable 7. Also connected in parallel with coil L ₁ is capacitor C ₄
is a bypass capacitor (capacitance is 68pF, for example) to pass the received signal of the FM broadcast band with low loss.
This is connected when the heater wire 2 (antenna) is used for both AM/FM.

By forming the first parallel resonant circuit 21 with the series circuit of coil L ₂ and coil L ₃ and the reactive capacitance C _f , and causing this parallel resonant circuit 21 to resonate in parallel,
The power receiving efficiency is increased by canceling the invalid power.
If 4 m of feeder cable 7 with a distributed capacitance of 30 pF/m is used, the reactive capacitance C _f is approximately 120 pF.
It is. In this case, the inductance of coil L ₂ is 180 μH, and the inductance of coil L ₃ is a steady value.
It is set as 140μH. The inductance of coil _L3 is given a frequency characteristic as described later.

When only the fixed inductance coil L ₂ is connected in parallel with the reactive capacitance C _f as shown in the circuit diagram in Figure 3, the reception band will be 800 to 1300 KHz as shown in the frequency characteristic diagram of reception sensitivity in Figure 4. and has a very narrow band.

In order to obtain broadband reception characteristics, the coil _L3 connected in series with the coil _L2 has an inductance-frequency characteristic as shown in FIG. i.e. 200KHz
In the low frequency band up to about
It is constant at 140μH, and for frequencies higher than 200KHz, the inductance decreases rapidly as the frequency increases, and in the AM reception band between ○ and ×, it is 95μH at 500KHz and 10μH at 1500KHz.
It is becoming.

The coil _L3 is formed, for example, by winding a 0.4φ wire seven times around a toroidal core (μ=5000) with high magnetic permeability.

Therefore, the total inductance L ₂ +L ₃ of the first parallel resonant circuit 21 is reduced from 275 μH to 190 μH in the reception band of 500 KHz to 1500 KHz. Therefore, the resonance point of the first parallel resonant circuit 21 shifts to a higher frequency range as the frequency of the received signal increases. Therefore, the frequency characteristics of the first parallel resonant circuit 21 become wider.

Furthermore, in order to improve low-frequency receiving sensitivity, a capacitor _C5 is connected in parallel with the coil _L3 to form a second resonant circuit 22. The capacitance of the capacitor _C5 is adjusted according to the reactive capacitance _Cf , and the second parallel resonant circuit 22 is caused to resonate at a low frequency around 800 KHz. For example, when the reactive capacitance C _f is 120 pF, the capacitance of this capacitor C ₅ is set to about 280 pF.

As described above, the first parallel resonant circuit 21 is caused to resonate in parallel in the middle and high ranges of the receiving band, and the second parallel resonant circuit 22 is caused to resonate in parallel in the low range of the receiving band. As a result, as shown by characteristic curve A in the reception sensitivity characteristic diagram of FIG. 6, good reception performance can be obtained over an extremely wide band. Note that this characteristic A is obtained when there is no series coil _L1 , which will be described next.

In order to further improve the reception sensitivity in the high frequency range, the coil L ₁ forming the reactive capacitance C _f and the low-pass filter 23 is provided as described above. Assuming that the inductance of this coil _L1 is approximately 47μH,
A kind of resonance occurs at approximately 2MHz with the 120pF reactive capacitance C _f , and as shown by characteristic curve B shown by broken line B in FIG. 6, the sensitivity in the middle and high ranges of the reception band is improved.

Although the matching circuit 20 is provided on the window glass 1 side in FIG. 1, it is provided on the tuner 19 side as shown in FIG.
A feeder cable 7 may be used to connect the two.
In this case, the reactive capacity is the ground capacity of the windowpane antenna using the heater wire 2 and the ground capacity of the cable 7 in parallel. Further, the matching circuit 20 may be incorporated into the tuner 19. When it is installed in the tuner 19, if it is installed in the AM tuner side, the antenna is
Even when used for both AM and FM, there is no need to provide capacitor _C4 for FM bypass.

In addition, by appropriately selecting the inductance value of coil _L3 and the magnetic permeability of the toroidal core,
A similar effect can be obtained even if the coil _L2 is omitted as shown in the circuit diagram of FIG. For example, when the feeder cable 7 is 3 to 4 m long and the reactive capacitance C _f is about 120 pF, the core material used has a magnetic permeability μ of about 2500 to 8000. And the inductance is frequency 500K
850μH in Hz and 1700KHz frequency
Wind the wire so that it has a resistance of 75 μH at
Form L ₃ .

Incidentally, the coil _L1 and the capacitor _C4 in FIG. 8 do not necessarily need to be provided, and may be added as required.

[Effect of idea]

As described above, the present invention is an automotive receiver in which a resonant coil is provided in parallel with the ground stray capacitance of the antenna when looking from the input end of the tuner to the antenna side. It uses at least one coil that has a core whose magnetic constant changes and whose inductance decreases as the receiving frequency increases. For this reason, simply providing an inductance with a constant value that resonates in parallel with the reactive capacitance results in a narrow band due to the high Q.
In the receiving band, at least one of the resonant coils has a core whose magnetic permeability changes depending on the frequency, and the inductance decreases as the receiving frequency increases. The resonant frequency changes, making it possible to compensate for gain reduction due to ground stray capacitance over a wide band. Therefore, the reception sensitivity of an antenna circuit with a large reactive capacity can be increased over the entire reception band with a simple configuration.

[Brief explanation of the drawing]

Figure 1 is a wiring diagram of an automobile rear window glass antenna to which the present invention is applied, Figure 2 is a circuit diagram of a matching circuit showing an embodiment of the present invention, and Figure 3 is a single parallel diagram for comparison with Figure 2. The circuit diagram of the resonant circuit, Figure 4 shows the receiving sensitivity when using the parallel resonant circuit of Figure 3.
Frequency characteristic diagram, Figure 5 is an inductance-frequency characteristic diagram of the coil used in the example, Figure 6 is a reception sensitivity-frequency characteristic diagram when the matching circuit of Figure 2 is used, and Figure 7 is a feeder cable. Fig. 8 is a circuit diagram of a matching circuit showing a different embodiment from Fig. 2, Fig. 9 is a wiring diagram of a conventional window glass antenna,
FIG. 10 is an equivalent circuit diagram of FIG. 9. In addition, in the symbols used in the drawings, 1...rear window glass, 2...heater wire, 7...feeder cable, 19...tuner, 20...matching circuit, 21...first parallel resonant circuit, 22 ...Second
parallel resonant circuit, 23...low pass filter,
L ₃ ...resonant coil, C _f ...reactive capacitance.

Claims (1)

[Claim for Utility Model Registration] In an automobile receiving device in which a resonant coil is provided in parallel with the ground stray capacitance of the antenna when looking from the input end of the tuner to the antenna side, the resonant coil is provided with a transparent conductor according to the frequency. A receiver for an automobile using at least one coil that has a core with a varying magnetic property and whose inductance decreases as the receiving frequency increases.