JP2006344575A - Coaxial cable and its shield performance evaluation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coaxial cable capable of preventing invasion of noises by improvement of a shielding performance in a low frequency band and capable of achieving integration with a wire harness, and a shielding performance evaluation method of the coaxial cable in which the shielding performance can be evaluated without having labor, and at a low expense. <P>SOLUTION: In the coaxial cable 15 in which an outside conductor layer 17 is installed at the outer periphery of an inside conductor 3 covered by an insulator 4, and in which a sheath 7 is installed at the outer periphery, the outside conductor layer 17 is installed at the outer periphery of the insulator 4, and composed of a main conductor layer 18 of one layer in which a shielding resistance is set at 35 mΩ/m or less, and an auxiliary conductor layer 19 of one layer in which a shielding resistance of the whole outside conductor layer 17 is reduced to 3 mΩ/m to 6.5 mΩ/m. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a coaxial cable used for signal transmission (for example, a radio, a monitor image, etc.) in a vehicle such as an automobile, and a shielding performance evaluation method thereof.

  Conventionally, this type of general coaxial cable has a configuration as shown in FIGS. A coaxial cable 1 shown in FIG. 11 is provided with a single outer conductor layer (shielding layer) 5 on the outer periphery of an inner conductor (center conductor) 3 covered with an insulator 4, and a sheath (outer jacket) on the outer periphery thereof. 7 is provided. Further, the coaxial cable 2 shown in FIG. 10 is provided with two outer conductor layers 5 and 6 on the outer periphery of the inner conductor 3 covered with the insulator 4 in order to improve the shielding performance. 7 is provided. The outer conductor layers 5 and 6 are formed by braiding a plurality of metal strands in a mesh, laminating a plurality of metal strands, and laminating a metal vapor deposition layer on one side of a metal foil, a metal tape or a plastic tape. A composite tape that is vertically or horizontally wound is used (see Patent Document 1).

  As a method for evaluating the shielding performance of the coaxial cables 1 and 2, the transfer impedance method defined in the international standard IEC61196 is generally used. In this method, a transmission impedance measuring device 8 as shown in FIG. 13 is used, coaxial cables 1 and 2 having a specified length l are inserted into a metal pipe 9, current is supplied from the transmitter 10 side, and external conductors are connected. A method of measuring a voltage of the inner conductor 3 generated by coupling with an external electromagnetic field flowing through the layers 5 and 6, calculating a ratio between the output voltage U2 and the input voltage U1, and reading a transfer impedance with respect to the frequency by the spectrum analyzer 11. It is. The smaller this transfer impedance, the better the shielding performance of the outer conductor layers 5 and 6.

JP 2004-214137 A

  The coaxial cables 1 and 2 used for signal transmission (for example, radio, monitor images, etc.) in vehicles such as automobiles are affected by noise generated from noise sources such as wire harnesses, alternators and motors routed in the vehicle. It is easy to receive. The influence of noise disturbs sound and image signals of radio, television, navigation, etc., and appears as noise and image flickering. Therefore, conventional coaxial cables 1 and 2 are wire harnesses (W / H) that are noise sources. ) Was routed to another route away from.

  In recent years, with the trend of expanding the interior of a vehicle cabin, the routing route of the wiring material tends to be restricted or the routing space is reduced. The coaxial cable is arranged adjacent to the wire harness, 2 and the wiring harness are required to be integrated. When both are integrated, the LW band (153 to 279 kHz) which is a low frequency band, which has not been regarded as a problem in the past, the AM band (522 to 1710 kHz) used in AM radio, and the SW band (2.94 to 21) .975 MHz) and FM band (76 to 108 MHz), noise may intrude from the noise source. Therefore, the shielding performance of the coaxial cable may be improved in the low frequency band (LW band to FM band). It becomes necessary.

  However, at present, no design method has been established for developing a coaxial cable with improved shielding performance in the low frequency band. For this reason, the conventional coaxial cables 1 and 2 are not improved in shielding performance in the low frequency band, and noise may invade in the low frequency band. The coaxial cable is disposed adjacent to the wire harness (adjacent). Thus, it was difficult to integrate with the wire harness. Further, when developing such a coaxial cable, it is necessary to evaluate the shielding performance of the coaxial cable. However, the conventional shielding performance evaluation method based on the transmission impedance method is based on the fact that the transmission impedance measuring device 8 is expensive. There is a problem that the shielding performance evaluation method is expensive because it is necessary to make a large number of cable samples by trial and error and it takes time and effort (labor and time) to measure the transfer impedance.

  The present invention solves the above problems, improves the shielding performance in the low frequency band, prevents the intrusion of noise, and can be integrated with the wire harness and the shielding performance at low cost without trouble. The objective is to provide a method for evaluating the shielding performance of a coaxial cable.

  In order to achieve the above object, according to the first aspect of the present invention, in the coaxial cable in which the outer conductor layer is provided on the outer periphery of the inner conductor covered with the insulator, the shielding resistance of the outer conductor layer is 3 mΩ. / M to 6.5 mΩ / m.

  According to a second aspect of the present invention, in the coaxial cable according to the first aspect, the outer conductor layer is provided in a plurality of layers.

  The invention according to claim 3 of the present invention is the coaxial cable according to claim 2, wherein the outer conductor layer is provided on the outer periphery of the insulator, and the shielding resistance is set to one or more layers set to 35 mΩ / m or less. The main conductor layer is provided on the outer periphery of the main conductor layer, and one or a plurality of auxiliary conductor layers are provided to reduce the shielding resistance of the entire outer conductor layer from 3 mΩ / m to 6.5 mΩ / m. It is.

  According to a fourth aspect of the present invention, in the coaxial cable according to the third aspect, the diameter of the strand forming the auxiliary conductor layer is 0.5 mm or less.

  According to a fifth aspect of the present invention, in the coaxial cable according to the third aspect, the auxiliary conductor layer is made of a strand of strands or a stranded wire, and the pitch of the twisted body is 6 of the outer diameter of the shielding layer. It is characterized by being double to 60 times.

  According to a sixth aspect of the present invention, in the coaxial cable according to the third aspect, the auxiliary conductor layer is made of a strand of strands or stranded wires, and the pitch of the strands is 7 to 7 of the outer diameter of the shielding layer. It is characterized by being 40 times.

  According to a seventh aspect of the present invention, in the method for evaluating the shielding performance of a coaxial cable in which an outer conductor layer is provided on the outer periphery of an inner conductor covered with an insulator, the shielding resistance of the outer conductor layer is measured or calculated. The shielding performance is evaluated by the following.

  The invention according to claim 8 of the present invention is the coaxial cable shielding performance evaluation method according to any one of claims 1 to 6, wherein the shielding resistance of the outer conductor layer is set as the evaluation method according to claim 7. It is characterized in that the shielding performance is evaluated based on measurement or calculation and whether or not the obtained shielding resistance is 6.5 mΩ / m or less.

  According to the coaxial cable of the first aspect of the present invention, since the shielding resistance of the outer conductor layer is set to 3 mΩ / m to 6.5 mΩ / m, the shielding performance is improved in the low frequency band, and noise intrusion occurs. And can be integrated with the wire harness. In addition, since the evaluation of the shielding performance of the outer conductor layer is simplified, a coaxial cable having excellent shielding performance can be easily designed and developed.

  According to the coaxial cable of the second aspect of the present invention, since the outer conductor layer is provided in a plurality of layers, the shielding resistance of the outer conductor layer can be easily reduced and the shielding performance can be improved.

  According to the coaxial cable of the third aspect of the present invention, the outer conductor layer is composed of the main conductor layer and the auxiliary conductor layer. Therefore, when adjusting the shielding resistance of the outer conductor layer, the auxiliary conductor layer positioned outside is shielded. What is necessary is just to measure or calculate the shielding resistance of an external conductor layer by changing resistance. Therefore, the shielding resistance can be easily adjusted, and the shielding resistance of the outer conductor layer can be accurately and quickly set to a desired resistance value. In addition, since the shielding resistance of the main conductor layer is set to 35 mΩ / m or less, the main conductor layer is evenly coated on the outer periphery of the insulator so that the shielding performance does not vary and is stable, improving the shielding performance. It becomes easy to do. Furthermore, since the adjustment range of the shielding resistance of the auxiliary conductor layer can be widened, it becomes easy to adjust the shielding resistance of the entire outer conductor layer to 6.5 mΩ / m or less.

  According to the coaxial cable of the present invention, the shielding performance can be further improved by forming the auxiliary conductor layer using a conductor having a conductor diameter of 0.5 mm or less. Regardless of the wire diameter of the auxiliary conductor layer, it is possible to incorporate it into the wire harness only by setting the shielding resistance value to 6.5 mΩ / m or less. On the other hand, the shielding performance can be further improved by 10%. By improving the shielding performance, a cable with higher reliability and noise resistance can be obtained.

  According to the coaxial cable of the present invention, the production efficiency can be ensured by forming the auxiliary conductor layer at a pitch of 3 to 60 times the shielding layer outer diameter D (see FIG. 9B). Defects in the layer can be prevented. Furthermore, as in the coaxial cable according to claim 6, by forming the auxiliary conductor layer at a pitch of 7 to 40 times the shielding outer diameter, the flexibility is improved and the high frequency band (several MHz or more) shielding performance is achieved. Can be further improved. In addition, since the production speed is improved by increasing the pitch, the production cost can be reduced. However, while the manufacturing cost can be suppressed, if the pitch is greatly increased, not only the flexibility of the cable itself is deteriorated, but also the twist pitch is disturbed and the gap is generated at the time of bending. By setting the pitch to 7 to 40 times the outer diameter of the shielding layer, it is possible to create a cable while maintaining the flexibility required for W / H incorporation, and to improve the shielding performance at high frequencies. Therefore, the manufacturing cost can be reduced.

  According to the method for evaluating the shielding performance of the coaxial cable according to claim 7 of the present invention, since the shielding resistance (conductor electrical resistance) is used instead of the transmission impedance as a reference for evaluating the shielding performance of the outer conductor layer, the shielding resistance is Measurement can be performed easily and accurately using an inexpensive measuring device. In addition, it is not always necessary to make a sample of a coaxial cable and measure it, and only a sample of the outer conductor layer can be made and measured. Moreover, it can also calculate by numerical calculation instead of making a sample of a coaxial cable or an outer conductor layer. Furthermore, even when a sample of a coaxial cable or an outer conductor layer is prototyped, it is only necessary to prototype a sample of shielding resistance predicted by mathematical calculation, so that it is not necessary to trial a number of samples for trial and error. Therefore, the evaluation of the shielding performance of the coaxial cable can be performed efficiently and at a low cost with less effort than the conventional transfer impedance method.

  According to the method for evaluating the shielding performance of the coaxial cable according to claim 8 of the present invention, the shielding resistance of the outer conductor layer is measured or calculated, and whether or not the obtained shielding resistance is 6.5 mΩ / m or less is used as a reference. Therefore, it is possible to accurately evaluate whether or not the shielding performance of the coaxial cable is improved in the low frequency band, and the coaxial cable having improved shielding performance in the low frequency band. It can greatly contribute to design, development, testing, inspection, etc.

  Next, preferred embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a perspective view showing an embodiment of a coaxial cable 15 according to the present invention. In addition, the same code | symbol is attached | subjected to the thing of the same structure as the conventional coaxial cable.

  In the coaxial cable 15 of this embodiment, an outer conductor layer 17 is provided on the outer periphery of an inner conductor (center conductor) 3 covered with an insulator 4, and a sheath 7 is provided on the outer periphery thereof. The outer conductor layer 17 is provided on the outer periphery of the insulator 4 uniformly, that is, in close contact with a metal wire, metal tape, etc. described later, and has a shielding resistance of 35 mΩ / m. One main conductor layer 18 set as follows, and one auxiliary conductor layer 19 provided on the outer periphery thereof and reducing the shielding resistance of the entire outer conductor layer 17 to 3 mΩ / m to 6.5 mΩ / m. It is configured. Since the auxiliary conductor layer 19 has a function of adjusting the shielding resistance of the outer conductor layer 17, the auxiliary conductor layer 19 is not uniformly covered as shown in the main conductor layer 18, but is surrounded by a metal wire, tape, or the like. You may provide so that a clearance gap may be formed over one place or multiple places in a direction. Moreover, in order to further improve the shielding performance, the diameter of the conductor forming the auxiliary conductor layer can be reduced to 0.5 mm or less, thereby improving the shielding performance required for incorporation into the wire harness by 10%. It becomes. By improving the performance, it is possible to obtain a cable that is highly reliable and resistant to noise. Furthermore, by setting the pitch of the auxiliary conductor layer to about 7 to 40 times the outer diameter of the shielding layer, it is possible to obtain a cable that not only improves high-frequency shielding performance but also is low in cost and excellent in flexibility.

  The main conductor layer 18 and the auxiliary conductor layer 19 constituting the outer conductor layer 17 are formed by braiding a plurality of metal strands in a mesh, and winding a plurality of metal strands in the same direction or alternately (twisting together) ), Or vertically attached along the longitudinal direction of the inner conductor 3, or a composite tape obtained by laminating a metal deposition layer on one side of a metal foil, metal tape or plastic tape, or vertically wound (twisted). It consists of things. The main conductor layer 18 and the auxiliary conductor layer 19 may be provided in a plurality of layers instead of one layer as described above.

  When evaluating the shielding performance of the outer conductor layer 17 for the design, development, test, inspection, etc. of the coaxial cable 15 whose shielding performance has been improved in the low frequency band, the shielding resistance, not the transfer impedance, is used as a reference. Is used. When the shielding resistance is set to 3 mΩ / m to 6.5 mΩ / m, the shielding resistance of the main conductor layer 18 located on the inner side is set in advance to a predetermined value of 35 mΩ / m or less, and then placed on the outer side. A sample of the coaxial cable 15 or the outer conductor layer 17 in which the shielding resistance of the auxiliary conductor layer 19 to be selected is appropriately selected is manufactured, and the shielding resistance of the outer conductor layer 17 is measured to evaluate the shielding performance. When the measured value of the shielding resistance is larger than 6.5 mΩ / m, a sample of the coaxial cable 15 or the outer conductor layer 17 in which the auxiliary conductor layer 19 is replaced with another auxiliary conductor layer 19 having another shielding resistance is again obtained. A prototype is manufactured, and the shielding resistance of the outer conductor layer 17 is measured to re-evaluate the shielding performance. Such an operation is performed as many times as necessary to set the shielding resistance of the outer conductor layer 17 to 3 mΩ / m to 6.5 mΩ / m.

  When measuring the shielding resistance of the external conductor layer 17, for example, it can be measured using a shielding resistance measuring device 21 having a simple and inexpensive structure as shown in FIG. That is, a sample of the coaxial cable 15 or the outer conductor layer 17 having a predetermined length is prepared by prototyping, and both ends thereof are gripped by a gripping member 23 such as a chuck, and a current is supplied from the power source 25 to the outer conductor layer 17 through the gripping member 23. Then, the electrical resistance meter 27 measures the shielding resistance (conductor electrical resistance) of the outer conductor layer 17. And when the obtained measured value is 6.5 mΩ / m or less which is a criterion for pass / fail judgment, it passes (the shielding performance is improved), and when it is larger than 6.5 mΩ / m, it fails ( By determining that the shielding performance is not improved, the shielding performance of the outer conductor layer 17 is evaluated.

  The shielding resistance of the outer conductor layer 17 can also be calculated by mathematical calculation. The calculation formula is as shown in Formula (1).

ρ × 102 × 10-3
R = ―――――――――― × L (1)
S × 10-2

R is the shielding resistance of the outer conductor layer 17 (mΩ / m), ρ is the volume resistivity of the metal wire (μΩ · cm), S is the cross-sectional area (mm ² ) of the outer conductor layer 17, Number n, outer diameter dmm
Then, nπd2 / 4, L is the length (m) of the outer conductor layer 17.

  Therefore, assuming that the outer conductor layer 17 is configured by laterally winding (twisting) seven soft copper strands having an outer diameter of 0.32 mm, the volume resistivity value ρ of the annealed copper strand is 1. Since it is 742 μΩ · cm, the shielding resistance R is 30.96 mΩ / m as calculated by the equation (1). When the outer conductor layer 17 having this size is measured by the shielding resistance measuring device 21, the shielding resistance is 30.34 mΩ / m, and thus the theoretical calculation value of the shielding resistance R is in good agreement with the actually measured value.

  When the outer conductor layer 17 is composed of a plurality of layers, for example, the main conductor layer 18 and the auxiliary conductor layer 19, the shielding resistance R is the shielding resistance of each layer, that is, the shielding resistance R1 of the main conductor layer 18 and the auxiliary conductor layer. The calculation formula of the combined resistance when 19 shielding resistors R2 are connected in parallel can be applied. The calculation formula is as shown in Formula (2).

1
R = ----------------- (2)
1 / R1 + 1 / R2

  The reason why the shielding resistance of the outer conductor layer 17 is set to 3 mΩ / m to 6.5 mΩ / m is as follows.

  FIG. 3 shows frequencies in a low frequency band where noise intrusion is regarded as a problem on the horizontal axis, that is, LW band (153 to 279 kHz), AM band (522 to 1710 kHz), and SW band (2.94 to 21.975 MHz). (MHz) and FM band (76 to 108 MHz), the transfer impedance (mΩ / m) is taken on the vertical axis, and when the frequency is changed from LW band to FM band, the target performance value (T ) And the transfer impedance for different shielding resistances (Ra, Rb, Rc, Rd) of the outer conductor layer, respectively.

  In FIG. 3, T is a shielding that reduces the noise level by 20 dB or more in the LW band to SW band and by 10 dB or more in the FM band with respect to the shielding performance of the coaxial cable (1.5C2V) that is generally used conventionally. Since improvement in performance is desired, the frequency is changed from the LW band to the FM band, and a curve showing the target performance value of the transfer impedance of the outer conductor layer obtained so as to satisfy the requirement (reduction of 20 dB or more and 10 dB or more) is there. Further, Ra is a shielding resistance of 5.5 mΩ / m, Rb is a shielding resistance of 10.1 mΩ / m, Rc is a shielding resistance of 12.6 mΩ / m, and Rd is a frequency when the shielding resistance is 18.3 mΩ / m. Is a curve of transfer impedance obtained by changing the frequency range from LW band to FM band.

  As can be seen from the transfer impedance curve shown in FIG. 3, in the vicinity of 150 kHz which is the lower limit value of the LW band, if the transfer impedance of the outer conductor layer is 2.7 mΩ / m or less which is the target performance value (T), The shielding performance can be improved (improved) in all low frequency bands (LW band to FM band). In terms of the shielding resistance of the outer conductor layer, when the shielding resistance (Ra) is 5.5 mΩ / m, the transfer impedance is less than or equal to the target performance value (T) in all the LW band to FM band, and the shielding performance. Can be improved. However, when the shielding resistance (Rb) of the outer conductor layer is 10.1 mΩ / m, it becomes lower than the target performance value T in the AM band to FM band, and the shielding performance can be improved. Since the performance value T becomes higher than 2.7 mΩ / m, the shielding performance cannot be improved.

Therefore, as a result of investigating the relationship between the transfer impedance of the outer conductor layer and the shielding resistance in the vicinity of 150 kHz based on the above findings, as shown in FIG. 4, there is a strong correlation between the transfer impedance and the shielding resistance. I understand that there is. Therefore, when the target performance value of transfer impedance of 2.7 mΩ / m is set as the upper limit of the shielding performance pass line, the shielding resistance corresponding to the transfer impedance of 2.7 mΩ / m is 6 mΩ / m to 6.5 mΩ / m. Therefore, the shielding resistance of 6.5 mΩ / m becomes the upper limit of the passing line of the shielding performance, and the shielding resistance of the outer conductor layer is set to 6.5 mΩ / m or less, so that the low frequency band (LW band to FM band) ), The shielding performance is improved, and the intrusion of noise from the noise source can be surely prevented.
By the way, the lower the shielding resistance, the better the shielding performance, which is preferable, but the thickness of the outer conductor layer increases and the outer diameter of the coaxial cable becomes larger. Therefore, the lower limit value of the shielding resistance is set to 3 mΩ / m from an economical viewpoint.

  The reason why the shielding resistance of the main conductor layer 18 of the outer conductor layer 17 is set to 35 mΩ / m or less is as follows. That is, as shown in FIG. 5, when the shielding resistance of the main conductor layer 18 exceeds 35 mΩ / m, it becomes difficult to uniformly coat the main conductor layer 18 on the outer periphery of the insulator 4, and the shielding performance is improved. Variation occurs and becomes unstable. Further, it becomes difficult to lower the transfer impedance of the entire outer conductor layer 17 in the vicinity of 150 kHz to 2.7 mΩ / m or less, that is, the shielding resistance to 6.5 mΩ / m or less, and the shielding performance cannot be easily improved. . On the other hand, when the shielding resistance of the main conductor layer 18 is set to 35 mΩ / m or less, the main conductor layer 18 is uniformly coated on the outer periphery of the insulator 4 so that the shielding performance does not vary and is stable. It becomes easy to improve performance. Further, as shown in FIG. 6, since the adjustment range of the shielding resistance of the auxiliary conductor layer 19 can be increased with respect to the shielding resistance of the main conductor layer 18, the shielding resistance of the entire outer conductor layer 17 is 6.5 mΩ / m or less. Easy to adjust.

  The reason why the conductor diameter of the auxiliary conductor layer 19 is 0.5 mm or less is as follows. FIG. 7 shows how the transfer impedance value at 150 kHz changes with respect to the change in the diameter of the wire forming the auxiliary conductor layer. The figure shows a passing line (transfer impedance value of 2.7 mΩ / m) for achieving a shielding performance improvement of 20 dB and a passing line (transfer impedance value of 2 for improving the shielding performance by 10% (22 dB) from the target shielding performance value). .0mΩ / m) is also described. According to this, it is possible to make the target performance value (T) 20 dB improvement or less acceptable line regardless of the wire diameter, but by making it 0.5 mm or less, it is 10% of the target performance value 20 dB improvement. Thus, it is possible to achieve a 22 dB improvement with improved shielding performance and to realize a highly reliable and noise-resistant cable.

  The reason why the pitch of the auxiliary conductor layer (twisted body) 19 is 6 to 60 times the shielding layer outer diameter D (see FIG. 9B) is that the pitch is less than 6 times the shielding layer outer diameter D. This is because the production speed is remarkably lowered and the production efficiency cannot be ensured. Conversely, when the production rate exceeds 60 times, the production itself becomes difficult and the occurrence rate of defects increases. Therefore, in order to achieve both production efficiency and defect occurrence rate, the pitch is desirably 6 to 60 times.

The reason why the pitch of the auxiliary conductor layer 19 is 7 to 40 times the outer diameter D of the shielding layer (see FIG. 9B) is that when the pitch is 7 times or more, as shown in FIG. This is because the shielding performance in the vicinity) can be greatly improved and the manufacturing cost can be reduced. On the other hand, when the pitch exceeds 40 times, the flexibility deteriorates and the cable manufacturing itself becomes difficult. That is, in order to improve the shielding performance, flexibility, cost, and ease of production, it is desirable that the pitch be 7 to 40 times the shielding layer outer diameter D.
FIG. 8 shows the auxiliary conductor pitch index (pitch when the shielding layer outer diameter is 1), U-shaped bending characteristics, transfer impedance value at 10 MHz, and cost index (when the manufacturing cost of the current coaxial cable is 1). This shows the relationship of the manufacturing cost, and it can be seen that the U-shaped bending property (flexibility) is improved as the pitch (index) is lower.

(Embodiment 1)
As shown in FIG. 9A, the coaxial cable 15 of the present embodiment is an annealed copper wire having an outer diameter (wire diameter) of 0.265 mm covered with an insulator 4 made of polyethylene and having an outer diameter of 1.61 mm. An outer conductor layer 17 is provided on the outer periphery of the inner conductor (center conductor) 3 made of a single wire, and a polyvinyl chloride sheath 7 extruded to a thickness of 0.5 mm is provided on the outer periphery. The outer conductor layer 17 includes a single main conductor layer 18 provided uniformly on the outer periphery of the insulator 4 and two auxiliary conductor layers 19 provided on the outer periphery thereof. The main conductor layer 18 is formed by braiding a tin-plated annealed copper wire having an outer diameter (wire diameter) of 0.10 mm in a mesh shape with a pitch of 15 mm and a braid density of 97%, and the shielding resistance is set to 29 mΩ / m. The auxiliary conductor layer 19 is configured by horizontally winding (twisting) 58 tin-plated annealed copper wires having an outer diameter of 0.26 mm in two layers in the same direction at a pitch of 60 mm, and has a shielding resistance of 5.64 mΩ / m. Set to The shielding resistance of the entire outer conductor layer 17 including the main conductor layer 18 and the auxiliary conductor layer 19 could be reduced to 4.74 mΩ / m.

(Embodiment 2)
As shown in FIG. 9B, the coaxial cable 15 according to the present embodiment has nine stranded wires obtained by twisting 19 tin-plated annealed copper wires having an outer diameter of 0.18 mm as the auxiliary conductor layer 19, and the main conductor. A layer having a shielding resistance of 3.8 mΩ / m is used which is horizontally wound around the outer periphery of the layer 18 in the same direction at a pitch of 60 mm. Other configurations and sizes are the same as those of the first embodiment. The shielding resistance of the entire outer conductor layer 17 of this embodiment could be reduced to 3.35 mΩ / m.

(Embodiment 3)
Although not shown, the coaxial cable 15 of the present embodiment has a total four-layer structure in which the outer conductor layer 17 includes two main conductor layers 18 and two auxiliary conductor layers 19. The first layer of the main conductor layer 18 is a tin-plated annealed copper wire with an outer diameter of 0.1 mm braided in a mesh shape with a pitch of 15 mm and a braid density of 99%, and the second layer is a tin-plated annealed copper wire with an outer diameter of 0.1 mm. Is braided in a mesh shape with a pitch of 15 mm and a braid density of 93%, and the first layer of the auxiliary conductor layer 19 (corresponding to the first to third layers of the main conductor layer 18) is tin-plated annealed copper having an outer diameter of 0.1 mm The wire is braided in a mesh shape with a pitch of 15 mm and a braid density of 93%, and the second layer (corresponding to the first to fourth layers of the main conductor layer 18) is a tin-plated annealed copper wire with an outer diameter of 0.1 mm at a pitch of 15 mm. A braided braid with a braid density of 88%. Other configurations are the same as those of the first embodiment. The shielding resistance of the entire outer conductor layer 17 of this embodiment could be reduced to 6.47 mΩ / m.

  As is clear from the above embodiment, the coaxial cable 15 of the present invention has a shielding resistance of the outer conductor layer 17 set to 3 mΩ / m to 6.5 mΩ / m. As a result, noise can be prevented from entering and integration with the wire harness can be achieved. Moreover, since the evaluation of the shielding performance of the outer conductor layer 17 is simplified, a coaxial cable having excellent shielding performance can be easily designed and developed.

  Further, when the outer conductor layer 17 is provided in a plurality of layers, the shielding resistance of the outer conductor layer 17 can be easily reduced and the shielding performance can be improved.

  Further, when the outer conductor layer 17 is composed of the main conductor layer 18 and the auxiliary conductor layer 19, when adjusting the shielding resistance of the outer conductor layer 17, the shielding resistance of the auxiliary conductor layer 19 located outside is changed. Then, the shielding resistance of the outer conductor layer 17 may be measured or calculated. Therefore, the shielding resistance can be easily adjusted, and the shielding resistance of the outer conductor layer 17 can be set accurately and quickly to a desired resistance value. Further, when the shielding resistance of the main conductor layer 18 is set to 35 mΩ / m or less, the main conductor layer 18 is uniformly coated on the outer periphery of the insulator 4 so that the shielding performance does not vary and is stable. It becomes easy to improve performance. Furthermore, since the adjustment range of the shielding resistance of the auxiliary conductor layer 19 can be widened, it becomes easy to adjust the shielding resistance of the entire outer conductor layer 17 to 6.5 mΩ / m or less. Further, by optimizing the wire diameter and pitch of the auxiliary conductor layer, the shielding performance can be further improved, and a cable having sufficient flexibility to be incorporated into W / H can be obtained at low cost. I can do it.

  The method for evaluating the shielding performance of the coaxial cable 15 according to the present invention uses a shielding resistance (conductor electrical resistance) instead of a transmission impedance as a reference for evaluating the shielding performance of the outer conductor layer 17. Measurement can be performed easily and accurately using the measuring device 21. Moreover, it is not always necessary to make a sample of the coaxial cable 15 and measure it, and only the sample of the outer conductor layer 17 can be made and measured. Further, instead of making a sample of the coaxial cable 15 or the outer conductor layer 17, it can be calculated by mathematical calculation. Furthermore, even when a sample of the coaxial cable 15 or the outer conductor layer 17 is manufactured, it is only necessary to manufacture a sample of the shielding resistance predicted by mathematical calculation, so that it is not necessary to make a large number of samples by trial and error. Therefore, the evaluation of the shielding performance of the coaxial cable 15 can be performed efficiently and at low cost with less effort than the conventional transfer impedance method.

  Further, when using the above-described shielding performance evaluation method, the shielding resistance of the outer conductor layer 17 is measured or calculated, and the shielding performance is determined based on whether or not the obtained shielding resistance is 6.5 mΩ / m or less. As a result of the evaluation, it is possible to accurately evaluate whether or not the shielding performance of the coaxial cable 15 is improved in the low frequency band, and the design, development, and development of the coaxial cable 15 with improved shielding performance in the low frequency band. It can greatly contribute to testing, inspection and the like.

It is a perspective view showing one embodiment of a coaxial cable concerning the present invention. It is a schematic diagram of the shielding resistance measuring apparatus which evaluates the shielding performance of the coaxial cable shown in FIG. It is a figure which shows the state from which the target performance value of the transfer impedance of an outer conductor layer and the transfer impedance with respect to the different shielding resistance of an outer conductor layer each change when a frequency is changed from LW band to FM band. It is a figure which shows the relationship between the transfer impedance of the outer conductor layer in the vicinity of 150 kHz, and shielding resistance. It is a figure which shows the relationship between the main conductor layer of an outer conductor layer, and transmission impedance. It is a figure which shows the relationship between the shielding resistance of the main conductor layer of an outer conductor layer, and the shielding resistance of an auxiliary conductor layer. It is a figure which shows the relationship between the strand diameter of an auxiliary conductor layer, and transmission impedance. It is a figure which shows the relationship between the pitch of an auxiliary conductor layer, transmission impedance, flexibility, and cost. (A) is sectional drawing which shows Embodiment 1 of the coaxial cable of this invention, (b) is sectional drawing which shows Embodiment 2. FIG. It is sectional drawing which shows the conventional coaxial cable. It is sectional drawing which shows the other conventional coaxial cable. It is a schematic diagram which shows the shielding performance evaluation method by the transmission impedance method of a coaxial cable.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 Inner conductor 4 Insulator 7 Sheath 15 Coaxial cable 17 Outer conductor layer 18 Main conductor layer 19 Auxiliary conductor layer 21 Shielding resistance measuring device 23 Gripping member 25 Power source 27 Electric resistance meter

Claims (8)

  A coaxial cable in which an outer conductor layer is provided on the outer periphery of an inner conductor covered with an insulator, wherein the outer conductor layer has a shielding resistance set to 3 mΩ / m to 6.5 mΩ / m. cable.   The coaxial cable according to claim 1, wherein a plurality of outer conductor layers are provided.   The outer conductor layer is provided on the outer periphery of the insulator, and one or a plurality of main conductor layers whose shielding resistance is set to 35 mΩ / m or less and the outer periphery thereof are provided, and the shielding resistance of the entire outer conductor layer is reduced. The coaxial cable according to claim 2, comprising one or a plurality of auxiliary conductor layers that are reduced to 3 mΩ / m to 6.5 mΩ / m.   The coaxial cable according to claim 3, wherein a diameter of the strand forming the auxiliary conductor layer is 0.5 mm or less.   The coaxial cable according to claim 3, wherein the auxiliary conductor layer is made of a strand of strands or stranded wires, and the pitch of the strands is 6 to 60 times the outer diameter of the shielding layer.   6. The coaxial cable according to claim 5, wherein the pitch of the twisted body is 7 to 40 times the outer diameter of the shielding layer.   In the method for evaluating the shielding performance of a coaxial cable in which an outer conductor layer is provided on the outer periphery of an inner conductor covered with an insulator, the shielding performance is evaluated by measuring or calculating the shielding resistance of the outer conductor layer. Coaxial cable shielding performance evaluation method.   7. The shielding resistance of the outer conductor layer is measured or calculated, and the shielding performance is evaluated based on whether or not the obtained shielding resistance is 6.5 mΩ / m or less. The shielding performance evaluation method of the coaxial cable in any one.

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