JP2011176675A - Indoor power line, and method of improving transmission characteristic of the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent degradation of communication quality by suppressing degradation of balancing of a transmission path caused by installation of a switch in one-side wire line of a branch power line, in power-line carrier communication using an indoor power line. <P>SOLUTION: An opening-closing switch SW for switching turning-on/off of current between two terminals is interposed in an intermediate part on one side of a pair of wire lines WL1, WL2 of a branch power line BL3; and, when a line length from one-side core power line ML of the pair of wire lines to a power load LD is larger than that on the other side when the opening-closing switch SW is on, a balancing element 3 for suppressing a phase difference due to a line difference between the pair of wire lines WL1, WL2 at a carrier frequency used for power line carrier communication is serially inserted on the other side of the pair of wire lines WL1, WL2. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an indoor power line used as a network for power line carrier communication provided with a branch power line that branches from a main power line and supplies power to a power load, and a transmission characteristic improving method thereof.

  In power line carrier communication, a network can be easily constructed and communicated by using an existing power line. In power line carrier communication using an indoor power distribution system power line, differential transmission is usually performed using a pair of wire lines in order to establish communication between two modem devices. In differential transmission, a pair of wire lines are driven separately by two signals with inverted phases, that is, signals with the sum of the signal outputs of both signals being zero. Differential transmission has several advantages over transmission schemes that use a single wire line. One of them is that when the wire line has ideal line characteristics, almost no radiant energy is generated. However, the actual line characteristics are never ideal, and the line impedance changes for each line pair.

  If the balance between the pair of wire lines is poor, a common mode current is generated on the communication line. If leakage radio waves due to the common mode current cannot be sufficiently suppressed, the influence on peripheral devices becomes a problem. In order to reduce the common mode current, various countermeasures such as impedance matching or attenuation of differential transmission signal power have been proposed in the modem device to be used.

Report on "Study Group on High-Speed Power Line Carrier Communications" 22, Ministry of Internal Affairs and Communications, December 2005

  In a power line of an indoor distribution system, as a factor of a decrease in the balance between a pair of wire lines, it opens and closes on one side of the branch power line that branches from the main power line and supplies power to a power load such as a lighting device or a ventilation fan When a switch (one-sided switch) is provided, when the one-sided switch is turned on, a difference occurs in the line length between a pair of wire lines from the main power line to the power load, resulting in mismatch in the reflected wave And when the cut-off switch is turned off, there is a difference in line length between a pair of wire lines from the main power line to the open cut-off switch, resulting in mismatch in reflected waves. .

  With reference to FIG. 1, the above-described decrease in the degree of balance will be described. In FIG. 1A, a power load LD such as a lighting device is provided at the tip of a branch power line BL branched from the main power line ML, and one wire line WL1 is cut halfway (intermediate point M). 2 shows a typical example of a branch power line circuit in which a pair of wire lines WL3 and WL4 extend from the open ends of the two and a cut-off switch SW is connected to the tip of the wire lines WL3 and WL4. Wire line WL1, wire line WL3, cut-off switch SW, wire line WL4 from core power line ML to intermediate point M, wire line WL1, intermediate line M to power load LD, power load LD, wire line A loop-shaped current path that returns to the main power line ML through the WL2 in order is formed, and energization of the current path is controlled by turning on and off the one-side switch SW. Here, the line length of the wire line WL2 is “L”, the line length of the wire line WL1 from the main power line ML to the intermediate point M is “mL” (0 <m <1), and the intermediate point M to the power load LD. The line length of the wire line WL1 is “(1-m) L”, and the line lengths of the wire lines WL3 and WL4 are “nL” (n> 0).

  When the cut-off switch SW is turned off, the cut-off switch SW becomes an open end, and the signal wave incident from the main power line ML side is reflected by the cut-off switch SW. In this case, as shown in FIG. 1B, the line length of the path A passing through the wire line WL3 among the two paths from the main power line ML to the one-sided switch SW is “(m + n) L”, The line length of the path B passing through the wire line WL4 is “(2-m + n) L”, the line length of the path B is longer, and the difference is “(2-2m) L”. The route A side does not pass through the power load LD, but the route B side passes through the power load LD. On the other hand, when the cut-off switch SW is on, the cut-off switch SW does not become an open end, so that the signal wave incident from the main power line ML is reflected by the power load LD. In this case, as shown in FIG. 1C, the line length of the path A passing through the wire line WL3 among the two paths from the main power line ML to the power load LD is “(1 + 2n) L”, whereas the wire The line length of the path B that does not pass through the line WL3 is “L”, and conversely, the line length of the path A is longer, and the difference is “2 nL”. Therefore, regardless of whether the cut-off switch SW is on or off, the difference in the line length appears as a phase shift between the differentially transmitted signal waves, and the balance between the pair of wire lines is descend. Further, the decrease in the balance depends on the line lengths of the wire lines WL1 and WL2 and the wire lines WL3 and WL4 and the position of the intermediate point M, and further depends on the ON / OFF state of the one-side switch SW.

  In relation to the above problems, Chapter 5 and 5.1.4 “ON-OFF dependency of switch branching on frequency characteristics” of the “Study Group on High Speed Power Line Carrier Communication” (Non-Patent Document 1) In the section, it is reported as a phenomenon in which the intensity of the leakage electric field varies depending on whether the one-way switch is turned on or off. However, although the non-patent document 1 has reported that a difference occurs in the strength of the leakage electric field by turning on and off the one-way switch, what kind of line characteristic change appears and how to solve it? No method has been reported.

  Here, the problem that the line characteristics change when the one-sided switch is turned on and off is due to the provision of the one-sided switch. Therefore, the problem is solved by changing the one-sided switch to a two-way switch. However, in order to change the existing single cut switch to the double cut switch, the single cut switch is replaced with a double cut switch, and the wire line on the side where the single cut switch is not provided (in FIG. Wiring work is required to extend the line WL2) to the double cut switch. In addition, even when constructing a new indoor power line, the use of the double switch increases the cost.

  Further, there are cases where a three-way switch circuit for alternately turning on and off the power load of the lighting device or the like is provided at a plurality of locations such as both sides of the corridor and up and down the stairs. Next, referring to FIG. 2, a pair of switches in a case where a three-way switch circuit is provided on a wire line on one side of a branch power line that branches from the main power line and supplies power to a power load such as a lighting device. A change in the degree of unbalance between the wire lines will be described. For the three-way switch circuit shown below, the solution method of changing to the double switch is not practical because the three-way switch circuit needs to be configured in a double manner.

  In FIG. 2A, a power load LD such as a lighting device is provided at the tip of a branch power line BL branched from the main power line ML, and the wire line WL1 on one side is cut halfway (intermediate points M and N). The first terminal of the first three-way switch SW1 is connected to the point M, the first terminal of the second three-way switch SW2 is connected to the intermediate point N, and the second and second terminals of the first three-way switch SW1 are connected. The third terminal and the first and second terminals of the four-way switch SW3 are respectively connected, and the second and third terminals of the second three-way switch SW1 and the third and fourth terminals of the four-way switch SW3 are respectively connected. A typical example of a branch power line circuit using a three-way switch is shown. In this specification, a circuit between the intermediate points M and N including the two three-way switches SW1 and SW2 is referred to as a three-way switch circuit.

  In the three-way switch circuit shown in FIG. 2A, only one of the switches SW1 to SW3 is switched, so that conduction between the intermediate points M and N is alternately switched. Here, the three-way switches SW1 and SW2 are configured such that one is conductive while the other is non-conductive and the other is non-conductive between the first terminal and the third terminal. The four-way switch SW3 is switched between the first terminal and the third terminal, between the second terminal and the fourth terminal, and between the first terminal and the fourth terminal and between the second terminal and the third terminal. The state is switched alternately. The number of four-way switches SW3 provided in the three-way switch circuit may be 0 or 2 or more. Wire line WL1, from main power line ML to intermediate point M, three-way switch SW1, four-way switch SW3, three-way switch SW2, wire line WL1 from intermediate point N to power load LD, power load LD, A loop-like current path that returns to the main power line ML is formed via the wire line WL2 in order, and the energization of the current path is controlled by switching the switches SW1 to SW3. Here, as an example, the line length of the wire line WL1 from the main power line ML to the intermediate point M and the line length of the wire line WL1 from the intermediate point N to the power load LD are respectively “L”, and four lines from the three-way switch SW1. The line length from the switch SW3 to the three-way switch SW2 is “mL”, and the line length of the wire line WL2 is “nL”.

  In the circuit configuration illustrated in FIG. 2A, when the terminal pair on the side that is conductive in each of the switches SW1 to SW3 is continuous through the intermediate wire line, the intermediate points M and N are electrically connected. When the terminal pair that is conducted by any of the switches SW1 to SW3 is switched, the path A passing through the intermediate point M from the main power line ML is cut off from the intermediate point N at the second or third terminal of the three-way switch SW2, and the main power line A path B that passes from ML through the wire line WL2, the power load LD, and the intermediate point N is disconnected from the intermediate point M at the second or third terminal of the three-way switch SW1. Therefore, regardless of which of the switches SW1 to SW3 is switched, the open end of the branch power line BL becomes the intermediate points M and N, and the signal wave incident from the main power line ML side is reflected at the intermediate points M and N. In this case, as shown in FIG. 2B, of the two routes from the main power line ML to the open end, the line length of the route A is “(1 + m) L”, while the line length of the route B is “ (1 + m + n) L ”, the line length of the path B becomes longer, and the difference is“ nL ”. The route A side does not pass through the power load LD, but the route B side passes through the power load LD. On the other hand, when the intermediate points M and N are conducting, the intermediate point M and N is not an open end, so that the signal wave incident from the main power line ML is reflected by the power load LD. In this case, as shown in FIG. 2C, the line length of the path A passing through the switches SW1 to SW3 among the two paths from the main power line ML to the power load LD is “(2 + m) L”, The line length of the path B passing through the wire line WL2 is “nL”, and the magnitude relation between the line lengths of the path A and the path B is determined according to the magnitude relation between (2 + m) and n, and the difference is “| (2 + m -N) L | " Therefore, regardless of whether the intermediate points M and N are conductive or non-conductive, the difference in the line length appears as a phase shift between the differentially transmitted signal waves, and the balance between the pair of wire lines. The degree decreases. Further, the decrease in the balance depends on the wire length between the wire lines WL1 and WL2 and the intermediate points M and N, the position of the intermediate points M and N, and further, the conduction and non-conduction between the intermediate points M and N, that is, It also depends on the state of the three-way switches SW1, SW2, etc.

  As described above, when a cut-off switch or a three-way switch is provided on a wire line on one side of a branch power line that branches from the main power line and supplies power to a power load such as a lighting device, depending on the state of the switch As a result, a difference occurs in the line length from the main power line to the power load between the pair of wire lines constituting the branch power line or from the main power line to the open end, resulting in mismatch in the reflected wave, and transmission of the branch power line Characteristics are degraded. Therefore, in power line carrier communication using an indoor power line, there is a concern about deterioration in communication quality due to a decrease in the balance of the transmission path depending on the state of the switch provided in the branch power line.

  The present invention has been made in view of the above problems, and its purpose is to balance transmission lines caused by providing a switch on a wire line on one side of a branch power line in power line carrier communication using an indoor power line. It is in the point which suppresses the fall of communication quality by suppressing the fall of a degree.

  In order to achieve the above object, the present invention is a method for improving the transmission characteristics of an indoor power line used as a network for power line carrier communication, wherein the indoor power line branches from a main power line and supplies power to a power load 1 A branching power line comprising a pair of wire lines, and an opening / closing switch for switching on / off of a current between two terminals in the middle of one side of the pair of wire lines of the branching power line, or between the first terminal and the second terminal A three-way switch circuit provided at both ends for switching on / off of the current and on / off of the current between the first terminal and the third terminal so that one is on and the other is off. When the switch is on or when both ends of the three-way switch circuit are conductive, the line length from the main power line on one side of the pair of wire lines to the power load is A balancing element that suppresses a phase difference due to a difference in the line lengths of the pair of wire lines at a carrier frequency used for the power line carrier communication when the line length is longer than the line length on the side; A transmission characteristic improving method characterized in that it is inserted in series on the other side of the first is provided.

  Furthermore, the present invention is an indoor power line used as a network for power line carrier communication, which is a wire line on one side of a branch power line consisting of a pair of wire lines that branch from the main power line and supply power to a power load. On the way, an open / close switch that switches on / off of the current between the two terminals, or on / off of the current between the first terminal and the second terminal and on / off of the current between the first terminal and the third terminal. A pair of wires is provided when a three-way switch circuit provided with both ends of a three-way switch to be turned off is interposed and the open / close switch is on or between the two ends of the three-way switch circuit is conductive. The line length from the main power line on one side of the line to the power load is longer than the line length on the other side, and the carrier frequency used for the power line carrier communication is 1 Wire line of the line length difference suppressing balancing device the phase difference due to the provides the indoor power line to a first feature in that it is inserted in series to the other side of the pair of wire lines.

  Further, in the transmission characteristic improving method of the first feature or the indoor power line, a wire line having the same material and structure as the pair of wire lines and having the same length as the difference in the line length is used as the balancing element. Alternatively, it is preferable to use an inductor element, and it is more preferable that the balancing element is inserted into an end portion of the other wire line on the side close to the power load or in the vicinity of the end portion.

  Furthermore, in the transmission characteristic improving method of the first feature or the indoor power line, when the open / close switch is interposed in the middle of one side of the pair of wire lines of the branch power line, the open / close switch On the other hand, the second feature is that capacitors having an electric capacity of 1 nF to 100 nF are connected in parallel.

  Furthermore, in the transmission characteristic improving method of the first feature or the indoor power line, when the three-way switch circuit is interposed in the middle of one side of the pair of wire lines of the branch power line, the 3 A first capacitor having an electric capacity of 1 nF to 100 nF is connected between the first terminal and the second terminal with respect to any one of the three-way switches of the path switch circuit, and the first terminal and the first switch A third feature is that a second capacitor having an electric capacitance of 1 nF to 100 nF is connected between the three terminals.

  According to the transmission characteristic improving method of the first feature or the indoor power line, by providing a balancing element on the wire line on the side where the open / close switch of the branch power line or the 3-way switch circuit is not provided, the open / close switch or 3-way When the switch circuit is on or conducting, the difference in line length from the main power line to the power load is corrected, and the balance between the pair of wire lines from the main power line to the power load is improved, improving communication quality Can be planned.

  Furthermore, according to the transmission characteristic improving method or the indoor power line of the second or third feature, a high frequency band (2 MHz to 30 MHz) or more used for high-speed power line carrier communication such as HomePlug 1.0 specification or AV specification. Since the high-frequency signal wave passes through a capacitor having an electrical capacitance of 1 nF or more and 100 nF or less provided in the open / close switch or the 3-way switch, the open / close switch or the 3-way switch does not become an open end, and reflection does not occur at the location. Therefore, a change in transmission characteristics of the branch power line due to a change in the state of the switch provided on the wire line on one side of the branch power line is eliminated or greatly suppressed. As a result, even when the open / close switch or the three-way switch circuit is off or non-conductive, the balance between the pair of wire lines from the main power line to the power load is improved, so that the communication quality can be improved. In addition, a capacitor having an electric capacity of 1 nF or more and 100 nF or less is provided on a wire line on one side of the branch power line in order to block the passage of the frequency band from DC to the commercial AC power supply frequency (50 Hz or 60 Hz). ON / OFF of the power supply from the power supply to the power load can be controlled in the same manner as when no capacitor is provided.

A schematic diagram explaining the difference between the line length and the circuit diagram explaining the effect of the cut-off switch on the branch power line of the indoor power distribution system on the decrease in balance A schematic diagram for explaining the difference between the line length and a circuit diagram for explaining the influence of the three-way switch circuit on the branch power line of the indoor power distribution system on the decrease in balance. The circuit diagram which shows typically the typical example of the indoor power line provided with the branch power line which has the cut-off switch used as the application object of this invention The circuit diagram and principal part enlarged view which show typically the indoor power line provided with the branch power line which has the cut-off switch in 1st Embodiment of this invention 4 is a circuit diagram showing two types of measurement circuits each modeling the indoor power line shown in FIG. 4 and the indoor power line shown in FIG. Configuration diagram of a measurement circuit for measuring the common current of the measurement circuit shown in FIGS. The figure which shows the common current measurement result of the circuit for a measurement which applied the countermeasure of 1st Embodiment according to ON / OFF of a single-sided switch The figure which shows the common current measurement result of the circuit for a measurement which does not apply the countermeasure of 1st Embodiment according to ON / OFF of a cut-off switch The circuit diagram which shows typically the typical example of the indoor power line provided with the branch power line which has the three-way switch circuit which becomes the application object of this invention The circuit diagram and principal part enlarged view which show typically the indoor power line provided with the branch power line which has the three-way switch circuit in 2nd Embodiment of this invention The circuit diagram which shows typically the indoor power line provided with the branch power line which has the one-piece switch in 3rd Embodiment of this invention The figure which shows the simulation result which verified the selection range of the electric capacity of the capacitor The circuit diagram which shows the circuit for a measurement which modeled the indoor power line shown in FIG. Configuration diagram of a measurement circuit for measuring the transmission characteristics of the measurement circuit shown in FIGS. The figure which shows the common current measurement result of the circuit for a measurement which applied the countermeasure of 1st and 3rd embodiment according to ON / OFF of a cut-off switch The figure which shows the Smith chart which shows the reflective characteristic (S11) of the circuit for a measurement to which the countermeasure of 1st and 3rd Embodiment is applied, and attenuation | damping characteristic (S21) according to ON / OFF of a single cut-off switch. The figure which shows the reflection characteristic (S11) of the circuit for a measurement which applied only the countermeasure of 1st Embodiment, and the attenuation | damping characteristic (S21) according to ON / OFF of a one-way switch. The circuit diagram which shows typically the indoor power line provided with the branch power line which has the three-way switch circuit in 4th Embodiment of this invention

  An embodiment of an indoor power line and a method for improving the transmission characteristics of the indoor power line according to the present invention will be described with reference to the drawings.

[First Embodiment]
FIG. 3 schematically shows a typical example of the indoor power line 1 before applying the present invention, that is, to which the present invention is applied. Branch power lines BL <b> 1 to BL <b> 3 are branched from three locations of the main power line ML that is wired indoors from a power meter (not shown) via a distribution board (not shown). Outlets CT1 and CT2 are connected to the ends of the branch power lines BL1 and BL2, open when not in use, and connected to a power load when in use. A pair of wire lines constituting each branch power line BL1, BL2 is not provided with a one-way switch, a three-way switch, or the like. Accordingly, the branch power lines BL1 and BL2 have the same line length from the main power line ML of the pair of wire lines to the outlet or the power load regardless of connection / disconnection of the power load. A power load LD (for example, a lighting device or a ventilation fan) is connected to the tip of the branch power line BL3, and the wire line WL1 on one side of the pair of wire lines WL1 and WL2 constituting the branch power line BL3 is in the middle (intermediate) A pair of wire lines WL3, WL4 extend from the pair of open ends, and a one-side switch (open / close switch) SW is connected to the tip. The details of the branch power line BL3 to which the one-side switch SW is connected are the same as those described with reference to FIG. As a typical example, the outlets CT1 and CT2 are attached to the walls of different rooms, the power load LD is attached to the ceiling of a room, and the cut-off switch SW is attached to the wall of the same room as the power load LD. Assuming that As a result, if a commercially available PLC (Power Line Communication) adapter (modem device) for high-speed power line carrier communication is connected to the outlets CT1 and CT2, respectively, the outlets CT1 and CT2 (between two different rooms) can be operated at high speed. Power line carrier communication is possible. In addition, as a typical example, the main power line ML is configured with a pair of a neutral line of a commercial AC power source of a single-phase three-wire 200V and two voltage lines.

  Next, FIG. 4 shows an indoor power line 2 in which the present invention is applied to the indoor power line 1 shown in FIG. The difference between the indoor power line 1 shown in FIG. 3 and the indoor power line 2 shown in FIG. 4 is that the pair of wire lines WL3 and WL4 of the branch power line BL3 is not connected to the indoor power line 2 shown in FIG. This is the point that the balancing element 3 is connected to the open end where WL2 is cut halfway (intermediate point Q). In the first embodiment, as the balancing element 3, a cable having the same material and structure as the wire lines WL <b> 3 and WL <b> 4 and having a pair of wire lines WL <b> 5 and WL <b> 6 having the same length short-circuited is used. Accordingly, a pair of wire lines of the branch power line BL3 extending from the main power line ML to the power load LD has one side constituted by the wire lines BL1, BL3, BL4, and the other side constituted by the wire lines BL2, BL5, BL6, respectively. The line lengths of the lines are equal, and the decrease in the balance due to the difference in line length is suppressed.

  Regardless of the position of the intermediate point Q on the wire line WL2, the line lengths of the other wire lines BL2, BL5, BL6 are the same, so the position of the intermediate point Q is near the power load LD or the wire line The end of the power load LD side of WL2 may be used. In this case, there is an advantage that the work of connecting the balancing element 3 to the intermediate point Q can be easily performed from the ceiling or wall surface to which the power load LD is attached.

  As described above with reference to FIG. 1, when the cut-off switch SW is off, the difference in line length between the two paths from the main power line ML to the cut-off switch SW is “(2-2m) L”. When turned on, the difference between the lengths of the two route lines from the main power line ML to the power load LD is “2 nL”. Here, when the branch power line BL of FIG. 1 is applied to the indoor power lines 1 and 2 shown in FIGS. 3 and 4, the indoor power line 1 shown in FIG. 3 is not changed from the branch power line BL of FIG. In the indoor power line 2 shown in FIG. 2, when the cut-off switch SW is off, the difference in line length between the two paths from the main power line ML to the cut-off switch SW is “(2-2m + 2n) L”. The difference between the line lengths of the two paths from the ML to the power load LD is “0”. That is, the difference in line length at the time of on is a result of being added at the time of off. Therefore, in the indoor power line 2 to which the present invention is applied, the balance is obviously improved when the cut-off switch SW is turned on. On the other hand, when the cut-off switch SW is off, the line length difference is further increased by “2 nL”, but this increase does not necessarily reduce the off-state balance. The above-described phase shift that occurs when a signal wave reciprocates between the main power line ML and the one-sided switch SW is determined by a value obtained by dividing twice the difference in line length by the wavelength. By changing, it can be said that there is a possibility that the frequency may be improved at a frequency where the degree of balance has already decreased in a certain frequency range. Therefore, when viewed over the entire frequency range, the balance when the cut-off switch SW is off is not deteriorated on average, and the balance when the cut-off switch SW is on is reliably improved. become.

  Next, the effect when the present invention is applied will be verified based on specific measurement data. FIG. 5 shows a measurement circuit (circuit to be measured) in which the indoor power lines 1 and 2 shown in FIGS. 3 and 4 are modeled for experiments. The power line PL1 is obtained by integrating the main power line ML and the branch power line BL1 between the branch power lines BL1 and BL3, and the power line PL2 is obtained by integrating the main power line ML and the branch power line BL2 between the branch power lines BL2 and BL3. Outlets CT1 and CT2 are connected to the tip. Power lines PL1 and PL2 and branch power line BL3 are connected in parallel at branch point P, respectively. FIG. 5A corresponds to the indoor power line 2 after application of the present invention shown in FIG. 4, and the intermediate points M and Q are set at half the positions of the wire lines WL 1 and WL 2, respectively. FIG. 5 (b) corresponds to the indoor power line 1 before application of the present invention shown in FIG. 3, and the intermediate point M is set at a half position of the wire line WL1. In each of the measurement circuits shown in FIGS. 5A and 5B, two-core vinyl insulation manufactured by Showa Electric Cable System Co., Ltd. is connected to the power lines PL1 and PL2, the branch power line BL3, and the pair of wire lines WL3 and WL4. Using a vinyl sheath cable (flat 2 mm diameter), the power lines PL1 and PL2 each have a line length of 2 m, the branch power line BL3 from the branch point P to the intermediate points M and Q, and the intermediate points M and Q to the power load LD. The line length, the line lengths of the wire lines WL3, WL4 from the intermediate point M to the cut-off switch SW, and the line lengths of the wire lines WL5, WL6 extending from the intermediate point Q are each 3 m. In addition, the said cable used for the circuit for a measurement does not limit the specification etc. of the cable used for the main power line and branch power line which comprise the indoor power line 2 of this invention.

  6 shows a configuration diagram of a circuit for measuring a common current between the outlets CT1 and CT2 in each of the circuits for measurement shown in FIGS. 5 (a) and 5 (b). The measurement circuit shown in FIG. 6 is commonly used for FIGS. 5 (a) and 5 (b). The measurement circuit shown in FIG. 6 connects the first personal computer 10 and the outlet CT1 via the PLC adapter 12, and connects the second personal computer 11 and the outlet CT2 via the PLC adapter 13, and before the outlet CT2. The current probe 14 is provided at the measurement point P, and the current probe 14 is connected to the input port P 0 of the real-time spectrum analyzer 15. The first personal computer 10 and the PLC adapter 12 and the second personal computer 11 and the PLC adapter 13 are connected by an Ethernet cable (Ethernet is a registered trademark), respectively. As the PLC adapters 12 and 13, those commercially available by the applicant based on the HomePlug AV specification were used. For data transmission between the personal computers 10 and 11, data was transmitted from the personal computer 10 to the personal computer 11 using self-made software for measuring UDP (User Datagram Protocol) throughput.

  FIGS. 7 and 8 show the measurement results of the common current when the cut-off switch SW of the measurement circuit shown in FIGS. 5A and 5B is on and off. Comparing FIG. 7 and FIG. 8, in the frequency range around 4 to 5 MHz, 10 to 14 Mz, and 20 to 24 Mz, the off-state balance is not lowered and the on-state balance is improved. It can be seen that the balance is improved over the entire frequency range.

  In the first embodiment, the balancing element 3 is a cable having the same material and structure as that of the wire lines WL3 and WL4 and having a pair of wire lines WL5 and WL6 having the same length short-circuited. The purpose of connecting the balancing element 3 is to compensate for the phase shift caused by the difference in the line length. Therefore, an inductor element capable of causing a phase shift when connected and also capable of passing a direct current is provided. It can also be used as the balancing element 3. By the way, since the phase shift due to the difference in line length actually changes depending on the difference in line length and the carrier frequency, in order to improve the measurement result of the common current in the field in advance, It is also preferable to use one or more of the prepared several types of inductor elements having different inductances in series or in parallel as the balancing element 3.

[Second Embodiment]
FIG. 9 schematically shows a typical example of the indoor power line 4 before applying the present invention, that is, to which the present invention is applied. Branch power lines BL <b> 1 to BL <b> 3 are branched from three locations of the main power line ML that is wired indoors from a power meter (not shown) via a distribution board (not shown). Outlets CT1 and CT2 are connected to the ends of the branch power lines BL1 and BL2, open when not in use, and connected to a power load when in use. A pair of wire lines constituting each branch power line BL1, BL2 is not provided with a one-way switch, a three-way switch, or the like. Accordingly, the branch power lines BL1 and BL2 have the same line length from the main power line ML of the pair of wire lines to the outlet or the power load regardless of connection / disconnection of the power load. A power load LD (for example, a lighting device or a ventilation fan) is connected to the tip of the branch power line BL3, and a section in the middle of the wire line WL1 on one side of the pair of wire lines WL1 and WL2 constituting the branch power line BL3. A three-way switch circuit including two three-way switches SW1 and SW2 and a pair of wire lines WL3 and WL4 is provided (between the intermediate points M and N). The first terminal of the first three-way switch SW1 is connected to the intermediate point M, the first terminal of the second three-way switch SW2 is connected to the intermediate point N, and the second terminal of the first three-way switch SW1. And the second terminal of the second three-way switch SW2 are connected to both ends of the wire line WL3, respectively, and the third terminal of the first three-way switch SW1 and the third terminal of the second three-way switch SW2 are connected to the wire line WL4. Are connected to both ends. The three-way switches SW1 and SW2 are switched so that one is conductive while the other is non-conductive and the conductive non-conductive between the first terminal and the second terminal and the non-conductive between the first terminal and the third terminal. A four-way switch can be provided in the middle of the pair of wire lines WL3 and WL4 as shown in FIG. 2 (a). Suppose. When the intermediate points M and N are conductive, only one side of the pair of wire lines WL3 and WL4 is used. The details of the branch power line BL3 to which the two three-way switches SW1 and SW2 are connected are the same as those described with reference to FIG. As a typical example, the outlets CT1 and CT2 are attached to the walls of different rooms, the power load LD is attached to the ceiling of the staircase or the hallway, and the three-way switches SW1 and SW2 are located at positions separated from each other on the staircase or the hallway. Assume that it is attached to a wall. This enables high-speed power line communication between outlets CT1 and CT2 (between two different rooms) by connecting commercially available PLC adapters (modem devices) for high-speed power line communication to outlets CT1 and CT2, respectively. It becomes. In the second embodiment, in the indoor power line 4 shown in FIG. 9, the pair of wire lines of the branch power line BL3 extending from the main power line ML to the power load LD has a line length on the side passing through the three-way switch circuit. A case is assumed in which the length is longer than the length of the wire line WL2 that does not pass through the three-way switch circuit.

  Next, FIG. 10 shows an indoor power line 5 to which the present invention is applied to the indoor power line 4 shown in FIG. The difference between the indoor power line 4 shown in FIG. 9 and the indoor power line 5 shown in FIG. 10 is that the pair of wire lines WL3 and WL4 of the branch power line BL3 in the indoor power line 5 shown in FIG. This is the point that the balancing element 3 is connected to the open end where WL2 is cut halfway (intermediate point Q). In the second embodiment, as the balancing element 3, a pair of wire lines WL5 and WL6 having the same material and structure as those of the wire lines WL3 and WL4 are short-circuited. The line lengths of the pair of wire lines WL5 and WL6 are the line length of the path on the wire line WL1 side from the main power line ML to the power load LD in the branch power line BL3 of the indoor power line 4 shown in FIG. Let it be one half of the difference in the line length of the route. As a result, a pair of wire lines of the branch power line BL3 extending from the main power line ML to the power load LD is configured with the wire line BL1 and the wire line BL3 or BL4 on one side and the wire lines BL2, BL5, and BL6 on the other side. The respective line lengths are equal, and a decrease in the balance due to the difference in the line lengths is suppressed.

  Regardless of the position of the intermediate point Q on the wire line WL2, the line lengths of the other wire lines BL2, BL5, and BL6 are the same, so the position of the intermediate point Q is the same as in the first embodiment. It may be the vicinity of the load LD or the end of the wire line WL2 on the power load LD side. In this case, there is an advantage that the work of connecting the balancing element 3 to the intermediate point Q can be easily performed from the ceiling or wall surface to which the power load LD is attached.

  As described above with reference to FIG. 2, when the three-way switch circuit between the intermediate points M and N is non-conductive, the difference between the line lengths of the two paths from the main power line ML to the intermediate points M and N is At the time of conduction, the difference between the two path line lengths from the main power line ML to the power load LD is “| (2 + mn) L |”. Here, when the branch power line BL of FIG. 2 is applied to the indoor power lines 4 and 5 shown in FIGS. 9 and 10, the indoor power line 4 shown in FIG. 9 is not changed from the branch power line BL of FIG. In the indoor power line 5 shown in FIG. 3, when the three-way switch circuit is non-conducting, the difference between the line lengths of the two paths from the main power line ML to the intermediate points M and N is “(2 + m) L”. The difference between the line lengths of the two paths from the ML to the power load LD is “0”. That is, the difference in line length at the time of on is a result of being added at the time of off. Therefore, in the indoor power line 2 to which the present invention is applied, the balance is obviously improved when the cut-off switch SW is turned on. On the other hand, when the cut-off switch SW is off, the line length difference is further increased by “2 nL”, but this increase does not necessarily reduce the off-state balance. The above-described phase shift that occurs when a signal wave reciprocates between the main power line ML and the one-sided switch SW is determined by a value obtained by dividing twice the difference in line length by the wavelength. By changing, it can be said that there is a possibility that the frequency may be improved at a frequency where the degree of balance has already decreased in a certain frequency range. Therefore, when viewed over the entire frequency range, the balance when the cut-off switch SW is off is not deteriorated on average, and the balance when the cut-off switch SW is on is reliably improved. become.

  Since the effect when the present invention is applied is the same as that of the first embodiment, verification and explanation based on specific measurement data are omitted. In addition, it is possible to use an inductor element as the balancing element 3 as in the first embodiment.

[Third Embodiment]
In the first embodiment, in the indoor power line 2 shown in FIG. 4A, the balancing element 3 is connected to the open end where the wire line WL2 of the branch power line BL3 is cut halfway (intermediate point Q), and the one-way switch An improvement in the balance of the indoor power line when the cut-off switch SW is on was achieved without degrading the balance of the indoor power line when the SW was off on average. However, as described above, even after the balancing element 3 is connected, the difference between the line lengths of the two paths from the main power line ML to the cut-off switch SW when the cut-off switch SW is turned off is “(2-2m + 2n). ) L ″ still exists, and the degree of balance is reduced as compared with the case where there is no cut-off switch SW. On the other hand, at the time of ON, the difference between the line lengths of the two paths from the main power line ML to the power load LD is “0”. In the third embodiment, measures are taken to improve the decrease in the balance when the cut-off switch SW is off.

  FIG. 11 shows an indoor power line 6 in which a measure for improving the balance when the cut-off switch SW is turned off is applied to the indoor power line 2 to which the balancing element 3 shown in FIG. 4 is applied. The difference between the indoor power line 2 shown in FIG. 4 and the indoor power line 6 shown in FIG. 11 is that the indoor power line 6 shown in FIG. A capacitor C1 is connected between the terminals in parallel with the switch SW, and the one-sided switch unit 7 is configured. In FIG. 11B, the main part surrounded by a broken line is enlarged and displayed.

  The capacitor C1 is required to have a withstand voltage exceeding the peak voltage because the peak voltage of the AC or DC voltage supplied to the main power line ML is applied to both ends when the switch SW is opened (off). In the case of a commercial AC power supply with a single-phase three-wire 200V power supply voltage supplied to the power line ML, a withstand voltage of 250V or higher is used, and in the case of a DC power supply, for example, one having a withstand voltage of 630V or higher is used. In addition, when 2 to 30 MHz is assumed as the carrier frequency band of the high-speed power line carrier communication, the impedance of the capacitor C1 is given by 1 / 2πfc (f is the carrier frequency and c is the electric capacity of the capacitor C1). The electric capacity is preferably 1 nF or more and 100 nF or less. As a result, the signal wave of the high-speed power line carrier communication passes in the frequency band, but the impedance increases in the frequency band from DC to 60 Hz, and the supply of the power supply voltage is cut off. As a capacitor satisfying the above conditions, for example, a medium and high voltage ceramic capacitor (withstand voltage of 630 V, electric capacity of 10 nF) manufactured by Murata Manufacturing Co., Ltd. can be used.

  FIG. 12 shows a circuit simulation result verified with respect to the selection range of the capacitance of the capacitor C1. The power supply voltage supplied to the main power line ML is changed from 10 Hz to 100 MHz with an AC power supply having an amplitude of 50 V, and the electric capacity of the capacitor C1 is 6 types of 0.1 nF, 1 nF, 5 nF, 10 nF, 100 nF, and 1000 nF. Assuming the case where the parasitic capacitance of the main power line ML is 0.5 nF and the power load LD is a resistance load of 100Ω, the current flowing through the power load LD and the impedance of the capacitor C1 are calculated. From FIG. 12, it can be seen that the current increases when the frequency is 60 Hz and the capacitance of the capacitor C1 exceeds 100 nF. In addition, at 1 nF or less, the increase in impedance is significant, and a clear decrease in current is observed at 2 MHz or more. Therefore, the electric capacity of the capacitor C1 is preferably 1 nF or more and 100 nF or less, but more preferably 5 nF or more and 100 nF or less in order to suppress an increase in impedance with respect to a high frequency band of 2 to 30 MHz. Furthermore, in order to better suppress the increase in current at the commercial AC power supply frequency of 60 Hz, the upper limit of the electric capacity of the capacitor C1 is preferably set to be smaller than 100 nF. Therefore, more preferably, the electric capacity of the capacitor C1 is set in the range of, for example, 5 nF to 50 nF, and more preferably 5 nF to 20 nF. When the DC power is supplied to the main power line ML, the electric capacity of the capacitor C1 may be 100 nF or more, but considering the versatility as the one-side switch unit 7, it is 100 nF or less. Is preferred.

  Here, when the cut-off switch unit 7 is applied to the indoor power line 2 of the first embodiment shown in FIG. 4, a method of adding the capacitor C1 in parallel to the existing cut-off switch SW, There are two methods of replacing the switch SW with the one-piece switch unit 7 in which the one-piece switch SW and the capacitor C1 are connected in parallel, and the effect exerted in either case is the same. When there is no existing indoor power line and the indoor power line 6 of the third embodiment to which the present invention is newly applied is laid, a single-cut switch unit in which a single-cut switch SW and a capacitor C1 are connected in parallel as a single-cut switch. 7 may be used. In this case as well, the single-cut switch SW and the capacitor C1 may be individually connected in parallel to configure the single-cut switch unit 7 in the field.

  Next, the effect of adding the capacitor C1 in parallel to the one-side switch SW will be verified based on specific measurement data. FIG. 13 shows a measurement circuit in which the indoor power line 6 shown in FIG. 11 is modeled for experiments. The electric capacity of the capacitor C1 is 10 nF. Since power lines PL1 and PL2 are the same as those in the measurement circuit shown in FIG. FIG. 14 shows a measurement circuit for measuring S parameters (S11: reflection characteristics, S21: attenuation characteristics) when the sockets CT1 and CT2 have a four-terminal network with respect to the measurement circuits shown in FIGS. It is. The measurement circuit shown in FIG. 14 connects the first port P1 of the network analyzer 16 and the outlet CT1 via a 100Ω-50Ω impedance conversion balun 17, and connects the second port P2 of the network analyzer 16 and the outlet CT2 to 100Ω−. It is configured to be connected via a 50Ω impedance conversion balun 18.

  FIG. 15 shows the measurement results of the common current when the cut-off switch SW of the measurement circuit shown in FIG. 13 is on and off. The common current was measured using the measurement circuit shown in FIG. 6 as in the first embodiment. Comparing FIG. 7 and FIG. 15, it can be seen that the common current is substantially equal when the cut-off switch SW is on and off in the entire frequency range of 2 to 30 MHz. By connecting the balancing element 3 to the intermediate point Q, the balance at the time of on is improved, and further, by connecting the capacitor C1 in parallel to the one-side switch SW, the balance at the time of off is the same level as at the time of on. It can be seen that it has been improved.

  16 and 17 show measurement results of S parameters (S11: reflection characteristics, S21: attenuation characteristics) when the cut-off switch SW of the measurement circuit shown in FIGS. 5A and 13 is on and off. . FIG. 16 shows the characteristics when the cut-off switch unit 7 is applied (FIG. 13), and FIG. 17 shows the characteristics when the cut-off switch unit 7 is not applied (FIG. 5A). The reflection characteristic (S11) is shown, and each figure (b) shows the attenuation characteristic (S21). From FIG. 17, the reflection characteristics and attenuation between the outlets CT1 and CT2 are turned on and off when the cut-off switch SW is turned on and off only by connecting the balancing element 3 to the intermediate point Q without applying the cut-off switch unit 7. It can be seen that the characteristics are greatly different due to the influence of the difference in the line length at the off time. On the other hand, as shown in FIG. 16, in the case of the third embodiment in which the capacitor C1 is provided in parallel with the cut-off switch SW and the cut-off switch unit 7 is configured, the cut-off switch SW is turned on and off. Thus, the difference between the reflection characteristics and the attenuation characteristics between the outlets CT1 and CT2 is greatly suppressed, and there is almost no difference between the two characteristics. This confirms the measurement result of the common current shown in FIG.

[Fourth Embodiment]
In the second embodiment, in the indoor power line 5 shown in FIG. 10, the balancing element 3 is connected to the open end where the wire line WL2 of the branch power line BL3 is cut halfway (middle point Q), and between the middle points M and N On the other hand, the balance of the indoor power line when the three-way switch circuit is off is not deteriorated on average, and the balance of the indoor power line when the three-way switch circuit is on is improved. However, as described above, even after the balancing element 3 is connected, the difference between the line lengths of the two paths from the main power line ML to the intermediate points M and N when the three-way switch circuit is non-conductive is “(2 + m ) L ″ still exists, and the degree of balance is lower than when there is no three-way switch circuit. On the other hand, when the three-way switch circuit is conductive, the difference between the line lengths of the two paths from the main power line ML to the power load LD is “0”. In the fourth embodiment, measures are taken to improve the decrease in the balance when the three-way switch circuit is non-conductive.

  FIG. 18 shows an indoor power line 8 in which a measure for improving the balance when the three-way switch circuit is non-conductive is applied to the indoor power line 5 to which the balancing element 3 shown in FIG. 10 is applied. The difference between the indoor power line 5 shown in FIG. 10 and the indoor power line 8 shown in FIG. 18 is that the indoor power line 8 shown in FIG. Capacitors C2 and C3 are connected in parallel between the first and second terminals and between the first and third terminals, respectively, thereby constituting a three-way switch unit 9. In FIG. 18B, the three-way switch unit 9 surrounded by a broken line is enlarged and displayed. The three-way switch to which the capacitors C2 and C3 are added may be the second three-way switch SW2 on the intermediate point N side. It is sufficient if the capacitors C2 and C3 are connected to one of the two three-way switches SW1 and SW2. This is because the intermediate points M and N with respect to the signal in the high frequency band can be obtained by connecting a capacitor between any two terminals of the three-way switches SW1 and SW2 that are open at both the intermediate points M and N. This is because is not an open end. The above is the same even if a four-way switch is added between the two three-way switches SW1 and SW2, and it is not necessary to add a capacitor to the four-way switch as in the case of the three-way switch SW1.

  The capacitors C2 and C3 have the same specifications as the capacitor C1 described in the third embodiment. Therefore, each capacitance is preferably 1 nF or more and 100 nF or less, more preferably, for example, the capacitance of the capacitors C2 and C3 is set in the range of 5 nF to 50 nF, and more preferably 5 nF to 20 nF. Good to do.

  Here, when the above-described three-way switch unit 9 is applied to the indoor power line 5 to which the balancing element 3 shown in FIG. 10 is applied, capacitors C2, C3 are connected to any one of the existing three-way switches SW1, SW2. There are two methods, namely, a method of adding one of the existing three-way switches SW and SW2, and a method of replacing one of the existing three-way switches SW and SW2 with the three-way switch unit 9, and the same effects can be obtained in either case. When there is no existing indoor power line and the indoor power line 5 to which the three-way switch unit 9 is newly applied is laid, the three-way switch unit 9 is replaced with one of the three-way switches SW1 and SW2 as a three-way switch. Should be used. In this case as well, the capacitors C2 and C3 may be individually connected in parallel to one of the three-way switches SW1 and SW2, and the three-way switch unit 9 may be configured on site.

  The effect when one of the three-way switches SW1 and SW2 is configured as the three-way switch unit 9 is the same as the effect when the capacitor C1 is added in parallel to the one-side switch SW in the third embodiment. Verification and explanation based on specific measurement data are omitted.

[Another embodiment]
In the first and third embodiments described above, when a cut-off switch SW is provided on one side of a pair of wire lines as a branch power line that branches from the main power line ML and supplies power to the power load LD (first In the second and fourth embodiments, three-way switches SW1 and SW2 are provided on one side of a pair of wire lines as branch power lines that branch from the main power line ML and supply power to the power load LD. Although assumed to be provided (second type), the branch power line that branches from the main power line ML and supplies power to the power load LD is limited to one or two branch power lines of the first or second type. Instead of this, a configuration may be adopted in which a plurality of branch power lines arbitrarily combining the first or second type of branch power lines are branched from the main power line ML. The present invention shown in the first or third embodiment is applied to the power line, the first type branch power line, and the second type branch power line. Alternatively, the present invention shown in the fourth embodiment may be applied. In addition, when there are a plurality of first or second type branch power lines, it is preferable to apply the present invention according to the above type to all the branch power lines, but for some of the branch power lines. Even if the present invention is applied, the transmission characteristics can be improved.

  In each of the above embodiments, although not clearly indicated, the one-way switch SW, the three-way switch SW1, SW2, and the like are assumed to be manual switches for manually switching on / off or conduction paths. It may be a non-manual switch such as a possible switch, a timer-type switch, or a sensor-type switch that switches according to the detection signal of the sensor.

  Further, in each of the above embodiments, when the line length passing through the wire line WL1 from the main power line ML to the power load LD of the branch power line BL3 and the line length passing through the wire line WL2 are long on the wire line WL1 side. In the above description, the balancing element 3 is provided on the wire line WL2 side. However, when the line length on the wire line WL2 side is long, the balancing element 3 may be provided on the wire line WL1 side. .

DESCRIPTION OF SYMBOLS 1,4: Conventional indoor power line 2,5,6,8: Indoor power line which concerns on this invention 3: Balancing element 7: One piece switch unit 9: Three-way switch unit 10,11: Personal computer 12,13: PLC Adapter 14: Current probe 15: Real-time spectrum analyzer 16: Network analyzer 17, 18: Impedance conversion balun A, B: Path BL: Branch power line BL1-BL3: Branch power line C1-C3: Capacitor CT1, CT2: Outlet LD: Power Load ML: Core power line M, N, Q: Intermediate point P: Branch point P0: Real-time spectrum analyzer port P1, P2: Network analyzer port PL1, PL2: Power line SW: Cut-off switch (open / close switch)
SW1, SW2: 3-way switch SW3: 4-way switch WL1-WL6: Wire line

Claims (12)

A method for improving the transmission characteristics of an indoor power line used as a network for power line carrier communication,
The indoor power line includes a branch power line consisting of a pair of wire lines that branch from the main power line and supply power to a power load;
An open / close switch that switches on / off of current between two terminals in the middle of the one side of the pair of wire lines of the branch power line, or on / off of current between the first terminal and the second terminal, and the first terminal and the second A three-way switch circuit provided with a three-way switch that switches on and off the current between the three terminals so that one is on and the other is off is provided at both ends, and when the open / close switch is on, or the three-way switch When the line length from the main power line on one side of the pair of wire lines to the power load is longer than the line length on the other side when both ends of the circuit are conductive,
Inserting a balancing element that suppresses a phase difference caused by a difference in the line length of the pair of wire lines at a carrier frequency used for the power line carrier communication in series on the other side of the pair of wire lines. A characteristic transmission characteristic improvement method.   The transmission characteristic improving method according to claim 1, wherein a wire line having the same material and structure as the pair of wire lines and having the same length as the difference in the line length is used as the balancing element.   The transmission characteristic improving method according to claim 1, wherein an inductor element is used as the balancing element.   The transmission characteristic improvement according to any one of claims 1 to 3, wherein the balancing element is inserted into an end portion of the other side of the wire line close to the power load or in the vicinity of the end portion. Method.   When the opening / closing switch is interposed in the middle of the pair of wire lines of the branch power line, a capacitor having an electric capacity of 1 nF to 100 nF is connected in parallel to the opening / closing switch. The transmission characteristic improving method according to claim 1, wherein the transmission characteristic is improved.   When the three-way switch circuit is interposed in the middle of the one side of the pair of wire lines of the branch power line, with respect to any one of the three-way switches of the three-way switch circuit, A first capacitor having a capacitance of 1 nF to 100 nF is connected between the first terminal and the second terminal, and a second capacitor having a capacitance of 1 nF to 100 nF is connected between the first terminal and the third terminal. The transmission characteristic improving method according to claim 1, wherein connection is performed. An indoor power line used as a network for power line carrier communication,
An open / close switch that switches on / off of current between two terminals in the middle of a wire line on one side of a branch power line that is branched from a main power line and supplies power to a power load; or a first terminal A three-way switch circuit provided at both ends is provided with a three-way switch that switches on / off of the current between the second terminals and on / off of the current between the first terminal and the third terminal so that one is on and the other is off. When the open / close switch is turned on, or when both ends of the three-way switch circuit are conductive, the line length from the main power line on one side of the pair of wire lines to the power load is on the other side. Longer than the track length,
A balancing element that suppresses a phase difference due to a difference in the line length of the pair of wire lines at a carrier frequency used for the power line carrier communication is inserted in series on the other side of the pair of wire lines. An indoor power line characterized by that.   The indoor power line according to claim 7, wherein a wire line having the same material and structure as the pair of wire lines and having the same length as the difference in the line length is used as the balancing element.   The indoor power line according to claim 7, wherein an inductor element is used as the balancing element.   The indoor according to any one of claims 7 to 9, wherein the balancing element is inserted into an end portion of the other side of the wire line close to the power load or in the vicinity of the end portion. Power line.   The open / close switch is interposed in the middle of the pair of wire lines of the branch power line, and a capacitor having an electric capacity of 1 nF to 100 nF is connected in parallel to the open / close switch. The transmission characteristic improving method according to claim 7, wherein the transmission characteristic is improved.   The three-way switch circuit is interposed in the middle of the one side of the pair of wire lines of the branch power line, and the first terminal is connected to one of the three-way switches of the three-way switch circuit. A first capacitor having a capacitance of 1 nF to 100 nF is connected between the second terminals, and a second capacitor having a capacitance of 1 nF to 100 nF is connected between the first terminal and the third terminal. The transmission characteristic improving method according to claim 7, wherein the transmission characteristic is improved.

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