JP2005197130A - Coaxial cable - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coaxial cable having higher shield effect than that of a conventional one, which can be bundled with a wire harness when used for an antenna feeder to connect the antenna of a vehicle mounted AM receiver to a receiver body. <P>SOLUTION: A first outer conductor 4 forming a first shield layer is provided on the periphery of a first insulating material 3 provided on the periphery of a center conductor 2, a second outer conductor 6 forming a second shield layer is provided on the periphery of a second insulating material 5 provided on the periphery of the first outer conductor 4, and a third outer conductor 8 forming a third shield layer is provided on the periphery of a third insulating material 7 provided on the periphery of the second outer conductor 6. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a coaxial cable, and more particularly to a coaxial cable suitable for use as an antenna feed line for connecting an antenna of an in-vehicle AM receiver and a receiver body.

  Conventionally, as a coaxial cable, a coaxial cable having a one-layer shield structure in which one shield layer is provided on the outer periphery of the insulator provided on the outer periphery of the center conductor, or an outer periphery of the first insulator provided on the outer periphery of the center conductor. There is known a coaxial cable having a two-layer shield structure in which a first shield layer is provided and a second shield layer is provided on the outer periphery of a second insulator provided on the outer periphery of the first shield layer ( For example, see Patent Documents 1 and 2.)

  Such a coaxial cable is used, for example, as an antenna feeder for connecting an antenna and a receiver body in an in-vehicle AM receiver.

When routing the antenna feed line to the vehicle, conventionally, the antenna feed line is separated from the wire harness and another route is created for routing. The reason is that the in-vehicle AM receiver has a high antenna input impedance, so the antenna feed line easily picks up noise, and when it is wired together with the wire harness, various switching noises generated in the vehicle It is because it will get on the antenna feed line via the harness.
JP 2001-283651 A JP 2003-59349 A

  However, as described above, routing the antenna feeder line through a separate route from the wire harness is inefficient in assembling the wire harness, and it takes a lot of time to design because the alternate route is selected and designed. It is desirable that the antenna feeder and the wire harness are bundled together and routed in the same route.

  When the antenna feed line is bundled together with the wire harness, it is necessary to use a coaxial cable having a higher shielding effect than a conventional coaxial cable as the antenna feed line.

  By the way, in order to obtain a coaxial cable having a higher shielding effect than that of a conventional coaxial cable, an evaluation means for objectively evaluating the shielding effect numerically is required as the premise. However, in the past, such evaluation means did not exist.

  Therefore, the present inventor has newly found an evaluation circuit system that can objectively evaluate the shielding effect of a coaxial cable used as an antenna feeder in an in-vehicle AM receiver, and such an evaluation circuit system. Based on the above, a coaxial cable having a high shielding effect according to the present invention has been completed.

  That is, the object of the present invention is higher in shielding effect than before, and bundled together with a wire harness when used as an antenna feeder for connecting the antenna of an in-vehicle AM receiver and the receiver body. Another object is to provide a coaxial cable that can also be used.

  In order to solve the above-mentioned problem, the invention described in claim 1 is characterized in that a first outer conductor constituting a first shield layer is provided on the outer periphery of a first insulator provided on the outer periphery of the center conductor, and the first A second outer conductor constituting the second shield layer is provided on the outer periphery of the second insulator provided on the outer periphery of the outer conductor, and a third insulator is provided on the outer periphery of the third insulator provided on the outer periphery of the second outer conductor. The third outer conductor constituting the shield layer is provided.

  The coaxial cable according to the first aspect of the present invention has the first, second, and third shield layers and has a three-layer shield structure.

  Conventionally, there are a coaxial cable having a one-layer shield structure and a coaxial cable having a two-layer shield structure, and it has been sensuously grasped that the latter having one shield layer has a better shielding effect. However, conventionally, there is no evaluation means for objectively evaluating the shielding effect of the antenna feeding line in the in-vehicle AM receiver, and the quality of the shielding effect is grasped sensuously. However, it is not certain whether the shielding effect increases as the number of shielding layers increases. The coaxial cable with the two-layer shield structure and the coaxial cable with the three-layer shield structure may be the same in terms of shielding effect. It was thought.

  The present inventor newly found an evaluation circuit system that can objectively evaluate the shielding effect of the antenna feeder line in the in-vehicle AM receiver (detailed later), and based on this evaluation circuit system, When the shielding effect was measured for the conventional coaxial cable having a one-layer shield structure, the coaxial cable having a two-layer shield structure, and the coaxial cable according to the present invention having the three-layer shield structure, the coaxial cable according to the present invention has the most shielding effect. It was confirmed that it was excellent, and its shielding effect was able to reduce noise disturbance even when bundled with a wire harness. The invention described in claim 1 has been made in view of the above.

  According to the first aspect of the present invention, it is possible to obtain a coaxial cable having a higher shielding effect than before, and the shielding effect is for connecting the antenna of the in-vehicle AM receiver and the receiver body. Even if it is used as an antenna feed line and bundled together with a wire harness, noise disturbance can be reduced. Therefore, such a coaxial cable having a high shielding effect can be used as the antenna feeding line and bundled together with the wire harness and routed to the vehicle through the same route.

Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram showing an example of an embodiment of a coaxial cable according to the present invention.

  In the figure, reference numeral 1 denotes the coaxial cable of this example, and this coaxial cable 1 is used as an antenna feed line for connecting an antenna of an in-vehicle AM receiver and a receiver body, for example.

  In the coaxial cable 1, a first outer conductor 4 constituting the first shield layer is provided on the outer periphery of a first insulator 3 provided on the outer periphery of a center conductor 2. A second outer conductor 6 constituting a second shield layer is provided on the outer periphery of the second insulator 5 provided on the outer periphery. Further, a third outer conductor 8 constituting a third shield layer is provided on the outer periphery of the third insulator 7 provided on the outer periphery of the second outer conductor 6. That is, the coaxial cable 1 is a coaxial cable having a three-layer shield structure in which the first, second, and third shield layers are configured by the first outer conductor 4, the second outer conductor 6, and the third outer conductor 8. .

  The center conductor 2 is made of, for example, an annealed copper wire, and the first insulator 3, the second insulator 5, and the third insulator 7 are made of, for example, polyethylene. The first outer conductor 4, the second outer conductor 6, and the third outer conductor 8 are formed of, for example, a hollow copper braided wire.

  The coaxial cable 1 configured as described above includes a center conductor 2, a first insulator 3, a first outer conductor 4, a second insulator 5, a second outer conductor 6, and a third insulator 7, It can be obtained by forming a third shield layer on a coaxial cable having a two-layer shield structure configured with the second shield layer. That is, when there is a coaxial cable having the two-layer shield structure in advance, a third shield layer is formed on the third insulator 7 by covering a hollow copper braided wire that forms the third outer conductor 8. By doing so, the coaxial cable 1 can be obtained. Of course, the coaxial cable 1 is formed in the same manner as a known coaxial cable manufacturing method, in that order, the center conductor 2, the first insulator 3, the first outer conductor 4, the second insulator 5, the second outer conductor 6, and the third. Alternatively, the insulator 7 and the third outer conductor 8 may be formed.

  In addition, when an insulating sheath is required on the third outer conductor 8, the third outer conductor 8 is covered with a heat shrinkable tube made of synthetic resin, and then thermally contracted to cover the third outer conductor 8. An insulating sheath may be formed on 8. Moreover, you may form an insulation sheath by extrusion molding. Further, when a low-noise coaxial cable is required, the number of outer conductor layers may be increased, for example, a four-layer shield or a five-layer shield coaxial cable.

  Next, regarding the shielding effect of the coaxial cable 1 of the present example described above, the conventional one-layer shielded coaxial cable having one shield layer and the shield of the conventional two-layer shielded coaxial cable having two shield layers are used. This will be explained in comparison with the effect.

  First, a shield effect measuring apparatus for measuring the shield effect will be described. FIG. 2 shows the shielding effect when the coaxial cable 1 of this example, the coaxial cable of the one-layer shield structure, and the coaxial cable of the two-layer shield structure are used as an antenna feeding line in an in-vehicle AM receiver. It is a figure which shows the shield effect measuring apparatus for measuring.

  The shield effect measuring apparatus 10 shown in the figure has a circuit when a coaxial cable is used as an antenna feeder in an in-vehicle AM receiver, that is, a circuit equivalent to an actual in-vehicle circuit.

  The shield effect measuring apparatus 10 has a shield room 11, and a ground plane 12 formed of a conductive metal plate is provided in the shield room 11. On the ground plane 12, a coaxial cable 13 to be measured is provided. Specifically, the coaxial cable 13 to be measured is provided on a highly insulated foamed plastic (for example, styrofoam) 14 having a thickness of 5 cm placed on the ground plane 12. In other words, the coaxial cable 13 to be measured is provided at a height of 5 cm from the ground plane 12 via the highly insulating foamed plastic 14.

  The coaxial cable 13 to be measured has a pseudo receiver 15 connected to one end side and a pseudo antenna 16 connected to the other end side. The pseudo receiver 15 includes an active probe (Agilent 41800A) 17 and a 300Ω resistor 18, and is grounded to the ground plane 12. The pseudo antenna 16 includes a 15 pF capacitor 20 and a 30 Ω resistor 21 provided in a shield box 19, and is grounded to the ground plane 12. Reference numeral 22 denotes a 50Ω termination resistor connected to the pseudo antenna 16.

  A spectrum analyzer (8591EM manufactured by HP) 25 is connected to the pseudo receiver 15 via a cable 23 and an RF preamplifier (MH648A manufactured by Anritsu Co.). The settings of the spectrum analyzer 25 are 9 kHz for RBW (resolution bandwidth), 30 kHz for VBW (video bandwidth), and about 33 ms for Sweep Time.

  On the high-insulation foamed plastic 14 on the ground plane 12, an automotive thin-walled low-voltage electric wire 26 is provided assuming a wire harness. This thin low-voltage electric wire 26 for automobile is provided so as to run in parallel with the coaxial cable 13 to be measured in the parallel running section indicated by reference numeral 27. The parallel distance of the parallel section 27 is 100 cm. Further, the parallel running interval between the coaxial cable 13 to be measured in the parallel running section 27 and the thin-walled low-voltage electric cable 26 for automobiles is assumed when the wire harness and the antenna feed line are bundled together at the time of wiring to the vehicle. It is 0 cm.

  Both ends of the automotive thin low-voltage electric wire 26 are grounded, and a 50Ω termination resistor 28 is connected to one end. A power meter (E4419 manufactured by Agilent) 29 is connected to the other end of the thin-walled low-voltage electric wire 26 for an automobile. The power meter 29 is connected with a signal generator (HP 6644A) 32 via a cable 30 and an RF-PA amplifier (broadband power amplifier) 31, and the signal from the signal generator 32 is transmitted to the power meter 29. The thin-walled low-voltage electric wire 26 for automobile is supplied.

  The power meter 29 measures the power of the signal from the signal generator 32. The power meter 29 is provided with a bidirectional coupler (not shown), and the traveling wave power and the reflected power are separated by using the bidirectional coupler.

  When measuring the shield effect of the coaxial cable to be measured using the shield effect measuring apparatus 10 as described above, the coaxial cable 13 to be measured is connected to the pseudo receiver 15 and the pseudo antenna 16. Then, after setting the coaxial cable 13 to be measured in the measuring apparatus 10 in this way, a high frequency signal of 100 dBμV is generated from the signal generator 32. The high-frequency signal generated from the signal generator 32 is amplified by 20 dB by the RF-PA amplifier 31, is input to the power meter 29 through the cable 30, and is further supplied to the thin-walled low-voltage electric wire 26 for automobiles. The high-frequency signal generated from the signal generator 32 is radiated from the thin-walled low-voltage electric wire 26 for automobile, and this high-frequency signal is received by the coaxial cable 13 to be measured running along with the thin-walled low-voltage electric cable 26 for automobile. Become. The high frequency signal received by the coaxial cable 13 to be measured is input to the pseudo receiver 15, further input to the RF-preamplifier 24 via the cable 23, amplified by 30 dB, and input to the spectrum analyzer 25. Then, frequency analysis is performed by the spectrum analyzer 25, and the output voltage is measured.

Next, the result of the measurement performed by such a method will be described with reference to FIGS.
FIG. 3 is a diagram showing a spectrum analyzer measurement value (output voltage) for each measurement object, and FIG. 4 is a diagram showing a shield amount for each measurement object obtained from the measurement result.

  In the figure, reference numeral 40 is a graph showing measurement results for the coaxial cable 1 of this example, and reference numeral 41 is a coaxial cable having a two-layer shield structure (1.5C-2V high-frequency coaxial cord JIS C3501 coaxial cable having a one-layer shield structure). The graph which shows the measurement result about the outer periphery which gave the outer conductor and the vinyl sheath), and the code | symbol 42 are the graph which shows the measurement result about the coaxial cable (1.5C-2V high frequency coaxial cord JIS C3501) of a 1 layer shield structure is there.

  Here, the measurement result of the shield amount shown in FIG. 4 is obtained from the output power calculated based on the output voltage shown in FIG. 3 measured by the spectrum analyzer 25 and the traveling wave power inputted to the power meter 29. The attenuation is calculated and converted into a shield amount.

  When the measurement result is seen, the coaxial cable 1 of this example has the best shielding effect (shielding amount), and the shielding amount is 20 dB higher than the coaxial cable having the single-layer shield structure, and noise interference is reduced to 10 minutes. It can be seen that it can be reduced to 1. Generally, when a wire harness and an antenna feeder are bundled together, a shield amount that is 20 dB higher than that of a coaxial cable having a single-layer shield structure, that is, a shield effect that is 10 times greater is required. It turns out that this is satisfied.

  As described above, according to the coaxial cable 1 of this example, the shielding effect is higher than the conventional one, and the shielding effect reduces noise disturbance even when bundled together with a wire harness as an antenna feeder for an in-vehicle AM receiver. It is something that can be done. Therefore, the coaxial cable 1 of this example can be used as an antenna feeder for an in-vehicle AM receiver, and can be bundled together with the wire harness and routed to the vehicle through the same route.

The figure which shows an example of embodiment of the coaxial cable which concerns on this invention. The figure which shows the shield effect measuring apparatus for measuring the shield effect at the time of using a coaxial cable as an antenna feeder in in-vehicle AM receiver. The figure which shows the measured value (output voltage) of the spectrum analyzer about each measuring object. The figure which shows the amount of shielding about each measuring object obtained from the measurement result.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Coaxial cable 2 Center conductor 3 1st insulator 4 1st outer conductor 5 2nd insulator 6 2nd outer conductor 7 3rd insulator 8 3rd outer conductor

Claims (1)

A first outer conductor constituting the first shield layer is provided on the outer periphery of the first insulator provided on the outer periphery of the center conductor, and a second outer periphery of the second insulator provided on the outer periphery of the first outer conductor is provided. The second outer conductor constituting the shield layer is provided, and the third outer conductor constituting the third shield layer is provided on the outer periphery of the third insulator provided on the outer periphery of the second outer conductor. Coaxial cable.

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