JPS6123683B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a vehicle antenna that is attached to a pillar part of a vehicle at a small distance and supplies radio waves to a radio installed inside the vehicle.

[Conventional technology]

Conventionally, vehicle pillar antennas have been used in which a supporter is fixed to the pillar surface of the vehicle from the outside with screws, etc., the antenna is supported by this supporter, and the distance between the antenna element and the pillar surface is parallel. . Compared to other vehicle antennas, this pillar antenna is easy to install on vehicles, can be manufactured at low cost, is easy for drivers to operate during use, and has a good appearance, so it has been used in many vehicles in recent years. It is starting to be used.

[Problem that the invention seeks to solve]

However, when car radios for AM reception were the mainstream, even this pillar antenna was able to provide good reception, but as the usage rate of car radios for both AM and FM reception increased, the reception performance of this pillar antenna (especially FM The negative aspects of (about) have become a problem. The reason for this is, first, because the antenna element of the pillar antenna and the metal pillar surface are installed close to each other, so the reactance component becomes large, significantly increasing the mismatch with the car radio. be. The second reason is that when receiving both AM and FM with one antenna element,
One of the reasons is that it has been impossible to design matching in any reception area using normal means.
This second cause is related to the length of the feeder, since matching is done on the car radio side based on impedance (Ω) for FM and capacitance (pF) for AM. Pillar antennas require a long distance from the antenna installation location to the car radio, and on the other hand, feeders that can match both FM and AM are not available.

A specific example of this mismatch will be explained by comparing it with an embedded antenna conventionally embedded in the fender of a car.

First, the capacity of the antenna with the embedded antenna installed is 15pF, and the AM reception capacity of the car radio is set to 80pF, so if you connect the antenna and car radio using a feeder with a capacity of 65pF, the AM reception capacity will be 15pF. The best match is for To use this embedded antenna for FM reception, the car radio must be
The impedance on the FM side is usually set to 75Ω, so if you use an impedance of 75Ω, the AM
The best match is for Therefore, if you connect the antenna and car radio with a coaxial cable that has a capacitance of 65pF and an impedance of 75Ω,
This means that both AM and FM can be received in optimal conditions. Both the built-in antenna and the car radio
It is usually installed on the left side of the car, and since the two can be connected inside the car, the cable length can be as short as 1000 mm. Judging from this length, matching can be achieved by using a so-called high capacitance feeder with a capacitance of 65 pF/m.

Next, when using a pillar antenna, the capacity of the antenna when installed is 30pF, and the capacity on the AM side of the car radio is set to 80pF.
Matching can be achieved by connecting a feeder with a capacitance of 50pF. Furthermore, on the FM side of the car radio, matching can be achieved by using a feeder with an impedance of 75Ω as described above. Here, the pillar antenna is attached to the right pillar of the car, and the car radio is fixed to the left side inside the car, so the feeder that connects the two needs to have a length of 1200 to 1600 mm, and the above conditions are met. in order to satisfy
A low capacitance feeder with a characteristic of 31.2 to 41.6 pF/m is required. However, JIS standard coaxial cables have characteristics of 50Ω and 100±3pF, and 75Ω and 100±3pF.
There were only cables with characteristics of Ω and 67±3pF, and if a cable of this standard was used to connect a pillar antenna to a car radio, there would be a complete mismatch. This JIS standard does not stipulate coaxial cables that are compatible with pillar antenna connections; rather, the impedance and capacitance of the cable are determined by its coaxial structure, material, dielectric constant of the insulator, etc. It's something to put away. Therefore,
It is impossible to manufacture cables with similar shapes and structures that have extremely different impedance Ω and capacitance pF.

For the above reasons, conventionally, pillar antennas and car radios are constructed by concentrically arranging an outer sheathing member made by polymerizing insulating material, shielding wire, and outer sheathing material, while maintaining a certain gap between the core wire and the outer periphery of the core wire. (For example, see Utility Model Application Publication No. 121690/1983) and is connected with a low capacitance feeder that achieves a low capacitance of 30 to 40 pF/m, and is commonly used.
It matches the capacity of the AM receiving side. For this reason,
On the FM receiving side, for an impedance of 75Ω
A feeder with a moderate impedance of 100 to 120 ohms is connected, resulting in mismatch and reception with poor sensitivity.

[Means for solving problems]

In view of the above-mentioned drawbacks, the present invention provides a matching box between the coaxial cable that connects the pillar antenna and the car radio, allowing matching in both AM and FM reception conditions, and achieving good AM-FM performance with a single antenna. The present invention provides a vehicle antenna that can receive signals.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows the external appearance of this embodiment. A supporter 2 made of an insulating material such as resin is fixed to the base of an antenna element 1 made of a telescopic tube. A supporter 3 made of an insulating material such as resin is attached to the supporter 1 .
Both supports 2 and 3 have screws 4 and 5 inserted through them for fixing to the pillar. A coaxial cable 6 that conducts with the antenna element 1 is connected to the supporter 2, and a reactance element 7 as a matching device is connected to the coaxial cable 6. A coaxial cable 8 is connected to the reactance element 7, and a plug 9 to be inserted into the antenna terminal of a car radio is connected to the end of the coaxial cable 8. Figure 2 is the first
This figure specifically shows the configuration of the coaxial cable 6.
has a length of about 1/2λ, and the coaxial cable 8 has a length of about 1/4λ, and a series capacitor 10 for capacitance correction is provided between the core wire of the coaxial cable 8 and the plug 9. This λ is the wavelength of the FM to be received, and the frequency of the domestic band is set to about 80 to 82 MHz. FIG. 3 shows the inside of the reactance element 7, and there is a capacitor 11 inside the reactance element 7, and both ends of the capacitor 11 are connected to the core wires of the coaxial cables 6 and 8 and the ground wire, respectively.

FIG. 7 shows the state in which this embodiment is installed in a vehicle 12. Supporters 2 and 3 are screwed to the pillar portion of a vehicle 12, and the antenna element 1 is mounted with a space between the pillar surface and the pillar surface. Vehicle 1
A car radio 13 is fixed inside the car radio 2, and a plug 9 is connected to the antenna terminal of the car radio 13.

In this embodiment, since the capacitor 11 is interposed at the end of the coaxial cable 6, the reactance of the antenna element 1 is removed at the position of the reactance element 7, resulting in an impedance that is somewhat the same as the feeding point impedance. However, even in this state, the impedance is still high, so the impedance at the end of the coaxial cable 8, which is about 100+Ω, is further lowered to around 75Ω. In order to correct the capacitance, a series capacitor 10 is used to match the capacitance on the AM receiving side.

FIG. 9 shows a characteristic curve of frequency and VSWR when FM is received in the state shown in FIG. 7.

Figure 8 shows a conventional antenna element 1 and a car radio 1.
FIG. 9 shows a state in which 3 is connected by a coaxial cable 14, and the frequency VSWR characteristic curve of this conventional configuration is also shown in FIG.

As can be seen from FIG. 9, the FM reception characteristics are improved in this embodiment.

FIG. 4 is an external view showing another embodiment of the present invention.
Coaxial cables 6 and 8 are connected to a branch 15 as a matching box.
A branch cable 16 is connected to the branch 15. This branch cable 16
The core wire and ground wire are coaxial cables 6 and 8, respectively.
It is connected to.

FIG. 5 specifically shows numerical values for each part of the embodiment shown in FIG. 4, and the length of the antenna element 1 is 1400 mm.
mm, the length of coaxial cable 6 is approximately 1/2λ, 1500mm,
The length of the coaxial cable 8 is about 1/4λ, 620 mm, and the length of the branch cable 16 is 400 mm, and each of the cables 6, 8, and 16 is of a low capacity of 34 PF/m. Series capacitor 10 is in plug 9
is inserted, and this capacitance is 260pF.

In this configuration, the branch cable 16 generates a capacitance between its core wire and the ground wire, acts as a capacitor, and has the same effect as the reactance element 7 described above. And this branch cable 1
6 to an appropriate length, and after actually installing it in the vehicle 12, the end of the branch cable 16 can be cut and finely adjusted to obtain the best reception condition. Further, this embodiment has the advantage that it has a simpler structure and can be manufactured at a lower cost than the embodiment shown in FIG.

FIG. 6 shows still another embodiment of FIG. 4, which can be used when a car radio is provided with separate AM antenna terminals and FM antenna terminals. The coaxial cable 8
An FM plug 17 is connected to the branch cable 16, an AM plug 18 is connected to the branch cable 16, and a series capacitor 19 for capacitance correction is inserted into the AM plug 18.

In this embodiment, both AM and FM can be exclusively matched and received.

〔Effect of the invention〕

Since the present invention is configured as described above, it is possible to match both FM and AM frequencies with a simple configuration, and it is possible to improve the inconvenience when using a pillar antenna.

[Brief explanation of the drawing]

Figure 1 is an external view showing one embodiment of the present invention, Figure 2 is an external view showing one embodiment of the present invention.
Figure 3 is an explanatory diagram showing specific elements of the same as above,
FIG. 4 is an external view showing another embodiment of the present invention, and FIG.
The figures are explanatory diagrams showing specific elements of the same as above, Fig. 6 is an explanatory diagram showing another embodiment, Fig. 7 is an explanatory diagram showing the state in which this embodiment is installed in a vehicle, and Fig. 8 is an explanatory diagram showing the conventional example. FIG. 9 is a graph showing characteristic curves of frequency versus VSWR for the present embodiment and the conventional antenna. 1... Antenna element, 2, 3... Supporter, 4, 5
...Screw, 6,8...Coaxial cable, 7...Reactance element as matching device, 9...Plug, 10...Series capacitor, 11...Capacitor, 12...Vehicle, 13...Car radio, 14...Coaxial cable, 1
5... Branch, 16... Branch cable, 17... FM plug, 18... AM plug, 19... Series capacitor.

Claims (1)

[Claims] 1. An antenna element installed at intervals on a metal body surface such as a pillar of a vehicle, and an antenna element connected to this antenna element and having a length of approximately 1/2 wavelength relative to the FM frequency to be received. A matching box connected to the end of this coaxial cable, a coaxial cable that is connected to the matching box and has a length of approximately 1/4 wavelength for the FM frequency to be received, and this A vehicle antenna comprising a capacitance correction capacitor inserted between an end of a coaxial cable and an antenna terminal of a car radio to match the capacitance on the AM reception side. 2. The vehicle antenna according to claim 1, wherein the matching device is configured to be branchable.