JPH03112203A - Antenna shield box - Google Patents

Abstract

PURPOSE:To protect a CR composite element for signal line and an electronic equipment main body from an abnormally high voltage by setting the discharge start voltage of a discharge gap provided between an input signal line and a shield case lower than the discharge start voltage of the composite element. CONSTITUTION:The discharge gap G1 for signal line is inserted between a signal line 7 and the shield case 2 at this side of the CR composite element 13 for signal line. An input side shield electrode 15 is connected to an output side shield tube 6 at high impedance in DC fashion and low impedance in AC fashion via an element 10. When a strike by thunderbolt or the abnormally high voltage is applied from an antenna to transmitting a coaxial cable, etc., to the input side signal electrode 15 of an antenna shield box 1 the discharge of the discharge gap G1 for signal line is started when the discharge or voltage exceeds the discharge start voltage set in advance, then, it is transmitted to the high voltage shield case 2. Thereby, since no high voltage is directly transmitted to the signal line 7, a capacitor C1, a resistor R1 for discharge, and the electronic equipment main body can be protected.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an antenna shield box used in electronic equipment having unbalanced input/output terminals.

BACKGROUND ART AND PROBLEMS This type of antenna shield box includes, for example, an antenna shield box 2 that is used as an antenna input circuit unit when drawing electrical signals received by an antenna into an electronic device such as a tuner via a coaxial cable.
There is 1. FIG. 6 shows an electrical equivalent circuit of the antenna shield box 21.

In FIG. 6, the left side of the figure is the input side, and the right side is the output side. The antenna shield box 21 is composed of a metal shield case 22 and a CR composite element 23 for the signal line 30 and a CR composite element 27 for the silt a 31 housed in the shield case 22.

Although not shown, the input side signal electrode 33 of the antenna shield box 21 is connected to an antenna coaxial cable, etc., and the output side signal electrode 34 is connected to an electronic device main body (tuner, etc.)
connected to the signal circuit.

The CR composite element 23 includes a capacitor 25 and a discharge resistor 26.
and an element discharge gap 24 in parallel.

CR between the input side signal electrode 33 and the output side signal electrode 34
They are connected via the composite element 23 with high impedance for direct current and low impedance for alternating current.

Similarly, the CR composite element 27 consists of a parallel circuit of a shield line capacitor 28 and a discharge resistor 29.

The input-side shield electrode 31 and the output-side shield electrode 32 are connected via the CR composite element 27 with high impedance in direct current and low impedance in alternating current.

If an abnormally high voltage due to a lightning strike or induced lightning is applied to the signal line 30 of the antenna shield box 21 through a coaxial cable etc. from the antenna, the CR composite element 2
When the discharge gap 24 for element No. 3 exceeds a preset discharge starting voltage, a discharge occurs.

The discharge starting voltage is set to a value lower than the voltage at which the capacitor 25 and the discharge resistor 26 break down, thereby protecting the capacitor 25 and the discharge resistor 26. However, the discharged high voltage may be transmitted through the signal line 30 and applied to the main body of the electronic device, potentially destroying the electronic device.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to protect the CR composite element and electronic device body housed in the antenna shield box from dielectric breakdown and failure when an abnormally high voltage is applied to the antenna shield box.

Means for Solving the Problems In order to solve the above-mentioned problems, the antenna shield box according to the present invention has an air gap provided between the conductive discharge body connected to the signal electrode on the input side and the shield case. A signal line discharge gap is formed, and the discharge start voltage of the signal line discharge gap is set lower than the discharge start voltage of the signal line CR composite element.

In the above configuration, when an abnormally high voltage is applied to the signal line, a discharge occurs between the conductive discharge body connected to the signal electrode and the shield case, the high voltage is transmitted to the shield case, and the output is This prevents an abnormally high voltage from being transmitted directly to the side signal electrode. As a result, an abnormally high voltage is not applied to the signal line CR composite element or the main body of the electronic device.

Embodiments Hereinafter, embodiments of the antenna shield box according to the present invention will be described with reference to the accompanying drawings.

[First Embodiment] FIG. 1 is a diagram showing the structure of an antenna shield box 1, in which the left side of the figure is the input side and the right side is the output side. 2
is a substantially cylindrical conductive metal shield case. In this embodiment, a gap portion provided between a conductive discharge body connected to an input side signal electrode and a shield case forms a discharge gap.

The conductive discharge body 17 shown on the left side of the figure is the insulating resin body 1
8, it is fixed together with the signal line 7 in a state where it is connected to an input side signal electrode (not shown). Resin body 18
is fitted into a metal shield electrode 19 having a cylindrical structure. This shield electrode 19 is electrically connected to and fixed to the shield case 2. A gap portion provided between the conductive discharge body 17 and the inner wall of the shield case 2 forms a signal line discharge gap Gl (see FIG. 2).

The CR composite element 10 for shielded wire shown on the right side of the figure is
It is composed of a donut-shaped capacitor 3 for shield wire and a resistor 8 for discharge. The donut-shaped capacitor 3 has opposing electrodes 3b and 3c formed on a donut-shaped dielectric 3a, and a portion of the opposing electrode 3c is also drawn out to the opposing surface via the end surface of the dielectric 38. A resistor 8 bridging the opposing electrodes 3b and 30 is formed on the surface of the donut-shaped capacitor 3 by a method such as printing. This resistor 8 plays the role of discharging the charge accumulated in the donut-shaped capacitor 3. The counter electrode 3b is electrically connected to the inner wall surface of the shield case 2. Counter electrode 3c
is electrically connected to the outer wall surface of the shield tube (output side shield electrode) 6 made of conductive metal. A signal line 7 is inserted through this shielded tube 6, and the signal line 7 and the shielded tube 6 are connected by resin filled between them.
Fully insulated. Note that the signal line 7 may be an insulated cable such as a coaxial cable. The donut-shaped capacitor 3 and the shield tube 6 are surrounded by a filler 9 such as epoxy resin,
It is firmly attached to shield case 2.

A braided wire of a coaxial cable or the like is usually connected to the shield tube 6, and the tip thereof can be inserted into a tuner of an electronic device or the like using a connector.

The signal line 7 on the input side and the signal line 7 on the output side are connected via a signal line CR composite element 13 (see FIG. 2) housed in the shield case 2.

FIG. 2 shows an electrical equivalent circuit diagram of the antenna shield box 1 having the above structure. antenna shield box 1
It consists of a shield case 2, a signal line discharge gap G1 housed in the shield case 2, a signal line CR composite element 13, and a shield line CR composite element 10. Although not shown, antenna shield box 1
The input side signal electrode 15 is connected to a core wire of a coaxial cable or the like of one antenna. Similarly, the input side shield electrode 19 is also connected to a shield wire such as a coaxial cable of the antenna.

On the other hand, the output side signal electrode 16 is connected to a signal circuit of an electronic device such as a tuner. Similarly, the shield tube (output side shield electrode) 6 is connected to the ground of the main body of the electronic device or to the shield circuit.

The signal line discharge gap G1 is the signal line CR composite element 1.
3, in front of signal line 7 and shield case 2
inserted between. The discharge start voltage of the signal line discharge gap G1 is designed to be lower than the discharge start voltage of the CR composite element 13.

The CR composite element 13 is the same as the conventional CR composite element 23 shown in FIG. 6, and includes a capacitor C1 and a discharge resistor R.
1 and an element discharge gap GO. The signal electrodes 15 and 16 are connected via the CR composite element 13 with high impedance in direct current and low impedance in alternating current.

The CR composite element 10 consists of a parallel circuit of a shield line capacitor C2 and a discharge resistor R2. A CR composite element 10 is connected between the input side shield electrode 14 and the output side shield tube 6.
It is connected with high impedance for DC and low impedance for AC.

If an abnormally high voltage due to a lightning strike or induced lightning is transmitted from the antenna through a coaxial cable and applied to the signal electrode 15 on the input side of the antenna shield box 1, if it exceeds the preset discharge start voltage, the signal will be Discharge is started in the line discharge gap G1, and high voltage is transmitted to the shield case 2. As a result, high voltage is not directly transmitted to the signal line 7, thereby protecting the capacitor C1, the discharging resistor R1, and the main body of the electronic device.

[Second Embodiment] An antenna shield box 1' shown in FIG. 3 is obtained by adding one discharge gap to the antenna shield box 1 shown in FIG. 1. If a high voltage is transmitted from the signal line 7 to the shield case 2 via the signal line discharge gap G1, or if an abnormally high voltage is applied directly to the shield line (shield case 2, etc.) due to a lightning strike, etc.
There is a risk that the donut-shaped capacitor 3 located between the input side and the output side of the shield line may suffer dielectric breakdown, or that the discharging resistor 8 may suffer dielectric breakdown. Therefore, the discharge gap G2 is also provided in parallel in the CR composite element 10 for shield wire to avoid these risks.

That is, a discharge metal plate 5 is assembled to the right open end 2a of the shield case 2 with an insulating plate 4 interposed therebetween. The discharge metal plate 5 is electrically connected to the shield tube 6.

As shown in FIG. 4, the insulating plate 4 has a disk shape,
Slits 4b are provided in all directions from the center of the disk, and a hole 4a for the shield tube 6 is provided in the center. In this way, a shield wire discharge gap G2 is formed between the discharge metal plate 5 and the shield case 2. When an abnormally high voltage is applied to the shield case 2, a discharge occurs in the thickness direction of the insulating plate 4 in the gap formed between the discharge metal plate 5 and the shield case 2. At this time, the discharge starting voltage of the shield wire discharge gap G2 is set such that the discharge starting voltage added to the discharge starting voltage of the signal line discharge gap G1 is lower than the discharge starting voltage of the signal CR composite element 13. It's well designed.

FIG. 5 shows an electrical equivalent circuit diagram of the antenna shield box 1.

Even if an abnormally high voltage is applied to the input side signal electrode 15 or the input side shield electrode 19, the high voltage is transmitted to the shield tube (output side shield electrode) 6 of the antenna shield box 1' and is grounded to the electronic device body. Or it is sent to a shielded circuit to prevent damage to the electronic device itself. At the same time, the signal line CR composite element 13 and the shield line CR composite element 10 are also protected.

Note that the shape of the discharge gap in the antenna shield box according to the present invention is not limited to the above-mentioned embodiments, and can be modified in various ways within the scope of the gist.

Further, in the above embodiment, the shield wire donut-shaped capacitor 3 is arranged on the output side of the antenna shield box 1.1', but the invention is not limited to this, and it may be arranged on the input side. It may be something. At this time, the discharge gap G1 is on the input side and is short-circuited with the input side signal electrode 15 in terms of direct current.

1 Furthermore, depending on the destination, the discharge resistor may be omitted in the CR composite element on the signal line side and the shield line side.

Furthermore, the types of connectors on the input side and the output side, and the male-female relationship can also be selected arbitrarily.

As shown in FIGS. 2 and 5, when the signal line discharge gap G1 is provided between the signal electrode 15 on the input side and the signal line CR composite element 13, the signal line CR composite Since a high voltage is not directly applied to the element 13, the element discharge gap GO, which is conventionally provided, may be omitted.

Effects of the Invention As is clear from the above explanation, according to the present invention, even if an abnormally high voltage is applied to either the signal line or the shield line at the antenna input terminal, the high voltage is applied only to the shield line at the output side. Conveyed. Therefore, it is possible to prevent abnormally high voltage from being transmitted directly to the output side signal line, and it is possible to eliminate failures in the electronic device itself.

[Brief explanation of drawings]

2 Figure 1 shows the first antenna shield box according to the present invention.
A partial vertical sectional view showing the embodiment, and FIG. 2 is an electrical equivalent circuit diagram thereof. Fig. 3 is a partial vertical sectional view showing a second embodiment of the antenna shield box according to the present invention, Fig. 4 is a plan view of an insulating plate, and Fig. 5 is an electrical equivalent circuit of the embodiment shown in Fig. 3. It is a diagram. FIG. 6 is an electrical equivalent circuit diagram showing a conventional antenna shield box. 1.1'... Antenna shield box, 2... Shield case, 13... CR composite element for signal line, 15
...Input side signal electrode, 16...Output side signal electrode, 1
7... Conductive discharge plate, G1... Discharge gap for signal line.

Claims (1)

[Claims] 1. An antenna shield in which an input-side signal electrode and an output-side signal electrode, which are installed in an insulated state in a shield case, are connected via a signal line CR composite element housed in the shield case. In the box, an air gap provided between the conductive discharge body connected to the signal electrode on the input side and the shield case forms a signal line discharge gap, and the signal line discharge gap starts discharging. An antenna shield box characterized in that the voltage is set lower than the discharge start voltage of the signal line CR composite element.