JPH06197036A - Noise filter for glass antenna - Google Patents

Abstract

PURPOSE:To prevent a sensitivity change in the glass antenna depending on temperature by revising a capacitance of an adjustment capacitor at a low and a high temperature so as to prevent an impedance change in the noise filter. CONSTITUTION:A noise filter 40 preventing invasion of a noise current from a power supply circuit 50 to a heater 30 is provided to a connecting point between the power supply circuit 50 and bus bars 32, 33 of the heater 30. Two thermal switches 46, 47 turned on at a low temperature and turned off at a high temperature are connected to one terminal of a troidal coil 44 at the heater side. Two capacitors 48,49 are connected between the two thermal switches and ground respectively. Then the two capacitors 48, 49 are connected in parallel as the temperature decreases from a high temperature to a low temperature by the setting of the operating temperature of the thermal switches 46, 47. Thus, the impedance of the noise filter 40 is kept to an optimum value within a wide temperature range. Thus, the sensitivity change in the glass antenna depending on temperature is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter for preventing noise in a glass antenna for a vehicle, and more particularly to a noise filter for a glass antenna in which the temperature characteristic of impedance of the noise filter is compensated.

In vehicles such as automobiles, AM and F
For M radio reception, there is one having a so-called glass antenna formed on the rear glass by means such as printing or baking.

The glass antenna is usually provided on the same glass surface in proximity to the heat ray (defogger), which is usually provided for preventing fog on the rear glass. Therefore, in order to avoid induction of noise from the heat ray side. It is common to insert a noise filter between the heat wire and the power supply (battery) side.

[0004] Such a noise filter for a glass antenna needs to have an impedance that does not change even when the external temperature changes.

[0005]

2. Description of the Related Art FIG. 5 shows a conventional noise filter for a glass antenna, which includes a glass antenna 20, a heating wire 30, and a heating wire 30 provided in a glass window (rear glass) 10 in the rear part of an automobile body. The noise filter 40 and the power supply circuit 50 connected to each other are shown.

The glass antenna 20 is arranged in parallel with the main antenna 21 in which straight antenna elements are bent in an inverted S-shape in parallel with each other, and is arranged above and below the main antenna 21 at a specific position of the main antenna 21. It is composed of connected auxiliary antennas 22 and 23. The auxiliary antenna not only increases the effective height of the main antenna, but also couples with the heat wire 30 and absorbs the high frequency power induced in the heat wire to the main antenna 21 side. The induced power of the main antenna 21 is
The impedance matching is performed through the matching circuit 24, so that the radio receiver 25 receives the impedance.

The heating wire 30 is composed of a plurality of resistance lines 31 provided in parallel with the glass antenna 20, and bus bars 32 and 33 connecting both ends of the resistance line 31.
By supplying a battery voltage to the resistance line 31 via the lead wires 34 and 35 connected to the bus bars 32 and 33, the rear glass 10 is heated to remove fogging on the rear glass.

The noise filter 40 comprises a toroidal coil 44 in which two coils 42 and 43 are provided on a ring-shaped ferrite core 41, and a noise current flows from the power supply circuit 50 to the heat wire 30 to the glass antenna 20 side. Prevent induction.

In the power supply circuit 50, by connecting the battery 52 to the power supply side of the noise filter 40 via the defogger switch 51, current is supplied from the battery 52 to the heating wire 30 via the noise filter 40.

In FIG. 5, the sensitivity of the glass antenna 20 depends on the impedance of the noise filter 40. This is because the high frequency power exchanged between the heating wire 30 and the main antenna 21 changes according to the impedance of the noise filter 40. Therefore, an adjusting capacitor 45 is provided between the heat wire side input of the noise filter 40 and the ground so that the impedance of the noise filter 40 becomes the optimum value Z ₀ . Value C of capacitor 45
Due to variations in the ferrite core 41 and the like, _p is adjusted during manufacturing.

[0011]

FIG. 6 shows an example of impedance characteristics of a noise filter,
Shows the case where the value C _p of the adjusting capacitor 45 is selected to be the optimum value at the standard temperature T ₀ , and the impedance characteristic is kept at the optimum impedance Z ₀ in the temperature range of T _{1 to} T _{0 to} T _2. Be done. However, when the temperature is lower than the temperature T ₁ and when the temperature is higher than the temperature T ₂ , the impedance characteristic indicated by A greatly changes from the optimum impedance Z ₀ .

The temperature characteristic of the noise filter is mainly determined by the temperature characteristic of the ferrite core forming the toroidal coil. As it is, it is based on the impedance change of the noise filter at low temperature and high temperature.
A decrease in the sensitivity of the glass antenna cannot be avoided.

In order to prevent the impedance change of the noise filter at such a low temperature and a high temperature as described above, a toroidal coil having a good temperature characteristic may be used, but this causes a problem of high cost. There is.

Therefore, even at low temperature and high temperature,
In order to make the impedance characteristic of the noise filter the optimum impedance Z ₀ , the value of the adjusting capacitor 45 may be changed according to the temperature. In FIG. 6, B and C indicate that the value of the adjusting capacitor 45 is the optimum value C.
_It shows that the impedance of the noise filter is larger or smaller than _{p, and that} the impedance of the noise filter is close to the optimum impedance Z ₀ at temperatures T ₁ or lower and T ₂ or higher. However, conventionally, a temperature compensation method for changing the value of such an adjustment capacitor has not been known.

The present invention is intended to solve such a problem of the prior art, and to change the value of the adjusting capacitor in the noise prevention filter in the vehicle glass antenna at low temperature and high temperature. The present invention aims to provide a noise filter for a glass antenna, which prevents a change in the impedance of the noise filter based on the temperature characteristics of the toroidal coil that constitutes the noise filter, and thus prevents a change in the sensitivity of the glass antenna that depends on temperature. I am trying.

[0016]

According to the present invention, a glass antenna 20 provided on a rear glass 10 of a vehicle and a glass antenna 20 are provided so as to be coupled to the glass antenna 20 in parallel, and both ends thereof are short-circuited by bus bars 32 and 33, respectively. A toroidal coil 44 having two coils 42 and 43 for connecting the bus bars 32 and 33 and the power supply circuit 50 to the heating wire 30 including the plurality of resistance lines 31 and a heating wire side of the toroidal coil 44. Two temperature switches 46, 47 connected between one end and the ground, and temperature switches 46, 47
A noise filter 40, which is composed of two capacitors 48 and 49 that are respectively connected to the ground via 47,
By setting the operating temperature of the temperature switches 46 and 47, the impedance of the noise filter 40 is maintained at an optimum value in a wider temperature range.

[0017]

In some cases, the rear glass 10 of the vehicle may be provided with a glass antenna 20 for receiving radio and a heating wire 30. The heating wire 30 is composed of a plurality of resistance lines 31 whose both ends are short-circuited by bus bars 32 and 33, respectively, and is used to remove the fog on the rear glass by passing a current from the battery to the resistance lines 31.

In the portion where the bus bars 32 and 33 of the heating wire 30 and the power supply circuit 50 are connected, the heating wire 3 from the power supply circuit 50 is connected.
A noise filter 40 is provided to prevent a noise current from flowing into zero. The noise filter 40 includes a toroidal coil 44 having two coils 42 and 43 that connect the bus bars 32 and 33 and the power supply circuit 50, and two temperatures connected between one end of the toroidal coil 44 on the heating wire side and the ground. Switches 46, 47 and temperature switches 46,
It is composed of two capacitors 48 and 49 which are respectively connected to the ground via 47.

The heat wire 30 is provided in parallel with the glass antenna 20 so as to be coupled to the glass antenna 20, and exchanges high-frequency power with each other.
A capacitor 45 is provided between the heat wire input side and the ground to keep the impedance of the noise filter 40 at an optimum value in the operating frequency range.
Due to the temperature characteristics of No. 4, the impedance is not optimal at low and high temperatures.

In the present invention, the toroidal coil 44 is used.
To one end of the heat wire side of 2 is connected two temperature switches 45 and 46 which are turned on at low temperature and turned off at high temperature,
2 connected between ground via temperature switches 46 and 47
Individual capacitors 48 and 49 are provided.

By setting the operating temperature of the temperature switches 46 and 47, the two capacitors 48 and 49 are sequentially connected in parallel as the temperature changes from high temperature to low temperature. The impedance of the filter 40 can be maintained at the optimum value.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of the present invention, in which the same components as those in FIG.
Reference numerals 6 and 47 denote temperature switches (S _1, S ₂ ) whose on and off states change depending on the temperature, which are, for example, thermal reed switches, and are connected to one end of the toroidal coil 44 on the heating wire side. 48 and 49 are toroidal coils 44 when the switches 46 and 47 are turned on, respectively.
Of the capacitor (C
_p1, C _p2 ).

In the noise filter for a glass antenna according to the present invention, the switches 46 and 4 are operated at low temperature and high temperature.
Based on the operation of No. 7, the impedance characteristic of the noise filter is corrected to compensate for the sensitivity change of the glass antenna.

FIG. 2 shows the operation of the switch and the impedance characteristic of the noise filter in the embodiment of FIG. 1, in which (a) shows ON / OFF of the switches S _{1 and} S ₂ with temperature change. The change of state is shown, and (b) shows the temperature characteristic of the impedance Z ₀ .

As shown in FIG. 2 (a), the switch S ₁ is
It is turned on below the temperature T ₁ and turned off above the temperature T ₀ . Further, the switch S ₂ is turned on at the temperature T ₀ or lower,
It is turned off at the temperature T ₂ or higher. Therefore, above the temperature T ₂ , the switches S _{1 and} S ₂ are both off, and the capacitors C _{p1 and} C _p2 are not connected. When the temperature becomes lower than T ₂ , the switch S ₁ is turned off _{and the} switch S ₂ is turned on, so that only the capacitor C _p1 is connected between the heat wire side input of the noise filter and the ground. When the temperature becomes lower than T _1, both the switches S _{1 and} S ₂ are turned on, so that the capacitors C _{p1 and} C _p2 are both connected between the heat wire side input of the noise filter and the ground.

Therefore, the impedance characteristic of the noise filter in this case is as shown by the arrow in FIG.
From the high temperature range of the temperature T ₂ or higher to the low temperature range of the temperature T ₁ or lower, the temperature becomes almost constant.

FIG. 3 shows an example of the temperature switch according to the present invention, and shows an example of a break type thermal reed switch. In the figure, (a) shows the structure of the switch, and (b) shows its operation.

The thermal reed switch 60 is shown in FIG.
, Two cylindrical permanent magnets 61 and 62 are
The magnetic poles are arranged so that different poles face each other, a cylindrical variable magnetic permeability member 63 whose magnetic permeability changes depending on temperature is interposed, and reed switches 64 and 65 made of a magnetic material are provided at the center of the cylinder. is there.

The variable magnetic permeability member 63 of the thermal reed switch has a characteristic that the magnetic permeability is high at low temperatures, but the magnetic permeability decreases at high temperatures. Therefore, as shown in Fig. 3 (b), at low temperature, the magnetic flux φ ₁ is predominant and
₂ becomes 0, so the reed switches 64 and 65 are attracted to each other and turned on. On the other hand, at high temperature, the magnetic flux φ
₁ and the magnetic flux φ ₂ exist separately, and the reed switch 64,
In the part of 65, both magnetic fluxes cancel each other out and become almost 0,
Therefore, the reed switches 64 and 65 are not attracted and are turned off.

FIG. 4 illustrates the operation of the thermal reed switch. Thermal reed switch on,
Below the operating temperature T that defines the off boundary, the magnetic flux φ ₁ is large and the magnetic flux φ ₂ is 0. Therefore, the reed switch 6
The magnetic flux φ at the contact points of 3, 64 is large, and the thermal reed switch is turned on. On the other hand, at the operating temperature T or higher, the magnetic flux φ ₂ is large and almost equal in magnitude to the magnetic flux φ ₁ , but since the directions are opposite to each other, the magnetic flux φ at the contact portion is almost 0.
And the thermal reed switch is turned off.

[0031]

As described above, according to the present invention, in the noise prevention filter for the vehicle glass antenna, the temperature of the adjustment capacitor is adjusted at low temperature and high temperature by using the temperature switch such as the thermal reed switch. It is possible to prevent changes in the impedance of the noise filter based on the temperature characteristics of the toroidal coil that constitutes the noise filter, and thus to prevent changes in the sensitivity of the glass antenna that depend on temperature. A noise filter for an antenna can be realized.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing the operation of the temperature switch and the impedance characteristic of the noise filter in the embodiment of FIG. 1, in which (a) shows the on and off states of the switches S _{1 and} S _{2 with} the temperature change. (B) shows impedance Z ₀
Shows the temperature characteristics of.

FIG. 3 is a diagram illustrating a temperature switch according to the present invention, in which (a) shows the structure of the switch and (b) shows its operation.

FIG. 4 is a diagram for explaining the operation of the thermal reed switch.

FIG. 5 is a diagram showing a conventional noise filter for a glass antenna.

FIG. 6 is a diagram showing an example of impedance characteristics of a noise filter.

[Explanation of symbols]

 10 Rear Glass 20 Glass Antenna 30 Heat Wire 31 Resistance Line 32 Bus Bar 33 Bus Bar 40 Noise Filter 42 Coil 43 Coil 44 Toroidal Coil 46 Temperature Switch 47 Temperature Switch 48 Capacitor 49 Capacitor 50 Power Circuit

Claims (1)

[Claims] 1. A glass antenna provided on a rear glass of a vehicle, and a heating wire comprising a plurality of resistance lines provided in parallel with the glass antenna so as to be coupled to the glass antenna and having both ends short-circuited by a bus bar. A toroidal coil having two coils for connecting the busbars and the power supply circuit, two temperature switches connected between one end of the toroidal coil on the heating wire side and the ground, and the temperature switch, respectively. A noise filter composed of two capacitors connected between grounds is provided, and the impedance of the noise filter is kept at an optimum value in a wider temperature range by setting the operating temperature of the temperature switch. Noise filter for glass antenna.