JP3016066B2 - How to reduce the dead zone - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reducing a dead zone of a leaky coaxial cable.

[0002]

2. Description of the Related Art A transmitting device for transmitting information is provided for transmitting information on the ground, for example, notices, etc. to a worker under construction in an underground tunnel or the like by wireless communication. 2. Description of the Related Art A wireless communication system has been constructed in which a cable is connected and arranged on a ceiling of a tunnel or the like, and a carrier wave is leaked from the leaked coaxial cable and received by a receiver carried by an operator.

FIG. 3 is a layout diagram of a conventional leaky coaxial cable.
FIG. 4 is an explanatory diagram showing the distribution of the electric field strength of a leaked radio wave at a position close to a conventional leaky coaxial cable.

[0004] In Fig. 3, 21 is a transmitter, 5 is a coaxial cable, 2 is a leaky coaxial cable, 3 is a terminator, and 6, 9 are connectors. One end of the leaky coaxial cable 2 is connected to the connector 6
And the other end is connected to the terminator 3 through the connector 9.

With the above configuration, the carrier supplied from the transmitter 21 leaks from the slit 24 provided at a predetermined interval in the leaky coaxial cable 2 and
And can be received by the receiving antenna 22 provided in the. The carrier wave remaining in the leaky coaxial cable 2 without leaking from the slit 24 is reflected at the terminal and becomes a reflected wave.

For this reason, two waves having different phases of the carrier wave and the reflected wave coexist in the leaky coaxial cable 2 and cause mutual interference. If the phases of the two waves are shifted by a half wavelength, a null point and a null point are generated. A so-called weak electric field insensitive area is generated and a state in which reception is impossible. In order to prevent this phenomenon, a terminator 3 (dummy load) is provided at the end of the leaky coaxial cable 2 and the carrier is converted into energy in the terminator 3 and consumed as heat to prevent the generation of a reflected wave. .

[0007]

However, when the characteristic impedance of the leaky coaxial cable 2 completely matches the resistance value of the terminator 3, the energy of the carrier is completely converted to heat in the terminator 3. In practice, it is extremely difficult to completely match the characteristic impedance and the resistance value due to variations in the respective elements, and it is impossible to completely convert energy into heat.

[0008] Therefore, the remaining carrier wave that cannot be converted into heat is reflected by the terminator 3, and the generation of a null point due to mutual interference between the carrier wave and the reflected wave cannot be avoided. In this null point area, reception becomes unstable with a generally used receiving antenna having a length of 波長 wavelength.

That is, since the slits 24 provided in the leaky coaxial cable 2 are generally provided at intervals of about 5 cm in this kind of leaky coaxial cable, the receiving antenna 22 is particularly provided for the leaky coaxial cable 2. When used close to about 1 m, an unreceivable area occurs depending on the receiving position as shown in FIG.

In order to receive signals in this area, the length of the receiving antenna 22 is generally set to 1/2 of the normal length.
It must be longer than the wavelength and must be long enough to extend beyond the dead zone to the region of the strong electric field.

For example, if the transmission frequency is 300 MHz, 1
The wavelength is lm, and the length of a general receiving antenna is 1/4.
25 cm of the wavelength, but more than 1/2 wavelength, ie, 50
cm or more.

Therefore, such a long receiving antenna 22
The receiver 23 is inferior in portability, and when mounted on a car or the like, avoids danger such as contact with the surroundings when moving.
There is a problem that the mounting place is restricted.
Furthermore, there is a problem that good reception cannot be obtained due to multipath due to reflected waves of radio waves leaked due to the surrounding environment in which the radio waves are installed.

An object of the present invention is to solve the problems of the prior art and to provide a method for reducing a dead zone caused by a leaky coaxial cable in order to obtain stable and good reception with a generally used half-wave antenna. With the goal.

[0014]

According to the present invention, there is provided a radio communication system using a leaky coaxial cable, wherein one end of the leaky coaxial cable is connected to the coaxial cable, and the coaxial cable is bent into an arc shape. By connecting the other end to one end of another leaky coaxial cable and arranging the two leaky coaxial cables in parallel, a portion of the other leaky coaxial cable facing the weak electric field strength portion of the leaky coaxial cable Is arranged so that the part is a part where the electric field strength is strong.

[0015]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is an explanatory diagram of a method for reducing a dead zone of a leaky coaxial cable according to an embodiment of the present invention. FIG. 2 is an explanatory diagram of the electric field intensity generated in each leaky coaxial cable according to the embodiment of the present invention. 1 and 2 are leaky coaxial cables according to the embodiment of the present invention, 4, 5 are coaxial cables, 3 is terminators, 6, 7,.
Reference numerals 8 and 9 denote connectors for connecting the cables.

A coaxial cable 5 is connected to one end of a leaky coaxial cable 2 according to the present invention via a connector 6, and the other end of the coaxial cable 5 is connected to an antenna connection terminal of a transmitter 21 for supplying a predetermined carrier. (Not shown). The other end of the leaky coaxial cable 2 is connected to a coaxial cable 4 via a connector 7. One end of the coaxial cable 4 is connected to the leaky coaxial cable 1 via a connector 8.
The terminal 3 is connected to the terminal via a connector 9. The coaxial cable 4 is bent in an arc shape, and the leaky coaxial cable 2 and the leaky coaxial cable 1
Are arranged in parallel.

The reason why the leaky coaxial cables 1 and 2 are connected via the coaxial cable 4 is that the phase of the carrier in the leaky coaxial cable 2 is adjusted by the coaxial cable 4 and the phase of the carrier transmitted to the leaky coaxial cable 1 is changed. This is also to minimize the radius of curvature at the time of bending.

Hereinafter, an example of the adjusting method using the coaxial cable 4 will be described. First, prepare three types of coaxial cables 4 of different lengths, connect the shortest one,
For example, a terminal connected to the connector 6 of the leaky coaxial cable 1 from a terminal connected to the connector 7 at a place about 1 m away from the leaky coaxial cable 1 by a measuring instrument such as an electric field strength meter that can measure the strength of radio waves. The strength of the radio wave is measured over the entire length up to.

When there is almost no strength of the radio wave, the leaky coaxial cables 1, 2 and the like are temporarily fixed in the same arrangement, and furthermore, the receiving condition is confirmed by an actually used receiver and finally fixed.

If the strength of the radio wave occurs, replace it with the next longer coaxial cable 4, measure the condition of the radio wave in the same manner, and if the strength of the radio wave occurs, replace the cable with the next longer one. Measure similarly.

Although the reception is mostly good by the above method, if the strength of the radio wave still remains, the strength of the radio wave is increased by moving the leaky coaxial cable 1 while keeping it parallel to the leaky coaxial cable 2. Can be fine-tuned, and a good reception state can be obtained.

Next, the operation of the carrier wave of the leaky coaxial cable when the method of reducing the electric wave dead zone according to the present invention will be described. First, when a carrier is output from the antenna connection terminal of the transmitter 21, it is supplied to the leaky coaxial cable 2 by the connector 6 via the coaxial cable 5. The supplied carrier wave reaches the terminator 3 through the leaky coaxial cable 2, the connector 7, the coaxial cable 4, the connector 8, the leaky coaxial cable 1, and the connector 9 as a traveling wave.

In the terminator 3, a reflected wave is generated due to a matching difference between the characteristic impedance of the leaky coaxial cables 1 and 2 and the resistance value of the terminator 3. This reflected wave is transmitted through connector 9,
The leaked coaxial cable 1, the connector 8, the coaxial cable 4, the connector 7, the coaxial cable 2, the connector 6, and the coaxial cable 5 reach the transmitter 21.

As described above, the mutual interference between the leaked coaxial cable 1 and the leaky coaxial cable 2 due to the traveling wave and the reflected wave occurs. As a result, the above-mentioned weak electric field null point occurs, as shown in FIG. In the leaky coaxial cables 1 and 2, points with weak electric field strength and points with strong electric field strength appear alternately.

Therefore, in the present invention, two leaky coaxial cables 1 and 2 are arranged in parallel, the phase of the carrier wave of the leaky coaxial cables 1 and 2 is adjusted by the coaxial cable 4, and the electric field strength of the leaky coaxial cable 2 is weak. The physical positions are determined and arranged such that the point having a strong electric field strength is located at a position facing the leaky coaxial cable 1 arranged in parallel with the point.

The leaky coaxial cables 1 and 2 complement each other with the above-described method of reducing the electric-wave dead zone, so that the electric field strengths are complemented by each other. The point where the electric field strength is weak is eliminated, and a strong electric field strength can be obtained uniformly. Even if the two leaky coaxial cables 1 and 2 are independently arranged in parallel without using the coaxial cable 4 and a carrier is supplied to each of the leaky coaxial cables 1 and 2, the same effect as in the above embodiment can be obtained. available.

[0027]

As is apparent from the embodiments described above, in the method for reducing the electric wave dead zone of the leaky coaxial cable according to the present invention, the reception which becomes a null point by integrally arranging the two leaky coaxial cables. It is possible to prevent the occurrence of a dead area, and it is possible to always ensure a good reception state in a case where a receiver is used in proximity to a leaky coaxial cable or in an environment where multipath occurs.

Accordingly, stable and good reception can be obtained at any place using a reception antenna having a normal length without lengthening the reception antenna.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a method for reducing a dead zone of a leaky coaxial cable according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram for explaining distribution of electric field intensity at a position close to a leaky coaxial cable according to an embodiment of the present invention.

FIG. 3 is a layout view of a conventional leaky coaxial cable.

FIG. 4 is an explanatory diagram showing a distribution of electric field strength of a leaked radio wave at a position close to a conventional leaky coaxial cable.

[Explanation of symbols]

 Reference Signs List 1 leaky coaxial cable 2 leaky coaxial cable 3 terminator 4 coaxial cable 5 coaxial cable 6 connector 7 connector 8 connector 9 connector 21 transmitter 22 receiving antenna 23 receiver 24 slit

Claims (3)

(57) [Claims] 1. A method for reducing a dead zone of a leaky coaxial cable, comprising connecting one end of a leaky coaxial cable A to a coaxial cable, bending the coaxial cable and connecting the other end of the coaxial cable to one end of a leaky coaxial cable B. By arranging the leaky coaxial cables A and B in parallel with each other, a portion of the leaky coaxial cable A where the electric field strength is weak and a position of the leaky coaxial cable B facing the portion where the electric field strength is weak are such that the electric field strength is low. A method of reducing a dead band of a leaky coaxial cable, wherein the leaky coaxial cables A and B are arranged so as to be strong parts, and a terminator is connected to the other end of the leaky coaxial cable B. 2. The method for reducing a dead zone of a leaky coaxial cable according to claim 1, wherein the coaxial cable is connected to the other end of the leaky coaxial cable B, and the other end of the coaxial cable is bent by bending the coaxial cable. By connecting to one end of the leaky coaxial cable C, the leaky coaxial cables A, B and C are connected.
Are arranged in parallel with each other, and the leakage is performed so that the portion of the leaky coaxial cable A and B where the electric field strength is weak and the position of the leaky coaxial cable C facing the portion where the electric field strength is weak are the portion where the electric field strength is strong. A method for reducing a dead zone of a leaky coaxial cable, comprising: arranging coaxial cables A, B and C, and further connecting a terminator to the other end of said leaky coaxial cable C. 3. The method for reducing a dead zone of a leaky coaxial cable according to claim 1, wherein the leaky coaxial cables A and B are provided.
Are arranged in parallel with each other, and the leaky coaxial cable is arranged such that a portion of the leaky coaxial cable A where the electric field strength is weak and a position of the leaky coaxial cable B facing the portion where the electric field strength is weak are the portions where the electric field strength is strong. A method for reducing the electric wave dead zone of a leaky coaxial cable, wherein A and B are arranged, and terminators are connected to the other ends of the leaky coaxial cable A and the leaky coaxial cable B, respectively.