JP2008236279A - Signal transmission system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a signal transmission system capable of achieving multiplexing even without a dedicated reception circuit by a pair of pair lines. <P>SOLUTION: The signal transmission system is provided with: a pair of a pair line composed of two conductor wires of an L1 line 4 and an L2 line 5; a set of first communication apparatuses connected to the pair line to use the pair line, performing signal transmission; and a set of second communication apparatuses connected to one line of the pair line and to a shield 6 to be a conductor to use the one line and the shield 6, performing signal transmission. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a signal transmission system in which a plurality of transmission devices connected to a transmission line perform communication (signal transmission) via the transmission line. In particular, the present invention relates to a system that multiplexes and transmits a plurality of types of signals through a pair of pair wires.

  Conventional signal transmission systems apply signal voltages in phase to multiple pairs of differential twisted pair wires, detect multiple pairs of common mode voltages as differential voltages on the receiver side, and affect differential voltage signals using twisted pair wires Multiplexing has been done without giving (For example, see Patent Document 1)

JP-T-2004-504733 (Claim 1, FIG. 1)

  In the conventional signal transmission system as described above, since a plurality of differential twisted pair wires are necessary for signal multiplexing, at least two pairs of signal wires are necessary, and applicable objects are limited. It was. In addition, a circuit for converting and reading the common-mode voltage into a differential voltage is required, and therefore, multiplexing is costly.

  Accordingly, an object of the present invention is to obtain a signal transmission system that can realize multiplexing by using a pair of paired wires without using a dedicated receiving circuit.

  A signal transmission system according to the present invention includes a pair of paired wires made of two conductive wires, a first communication device set connected to the paired wires and performing signal transmission using the paired wires, and the paired wires And a second set of communication devices that perform signal transmission using the one line and the conductor.

  According to the present invention, the first communication device set performs signal transmission using a paired wire, and the second communication device set performs signal transmission using one line and a conductor. Therefore, by transmitting signals by connecting between different lines, it is possible to perform good signal transmission with less interference and the like, and a widely available signal transmission system can be realized at low cost.

Embodiment 1 FIG.
FIG. 1 is a diagram showing a configuration of a signal transmission system according to Embodiment 1 of the present invention. In FIG. 1, the shielded cable (1) is composed of a pair of paired wires made up of two conductive wires, an L1 wire (4) and an L2 wire (5), and a shield (6). The shield (6) is a conductor (hereinafter referred to as a conductor) other than a pair of pair wires.

  For example, a set of A communication device (2) (hereinafter simply referred to as A communication device (2)) and B communication device (3) that respectively transmit two types of signals having different transmission methods to the shielded cable (1). For example, two sets (hereinafter simply referred to as B communication devices (3)) are connected to each other. Here, the A communication device (2) is connected so as to apply a signal represented by a voltage between the L1 line (4) and the L2 line (5) of the shielded cable (1). The B communication device (3) is connected so as to apply a signal represented by a voltage between one of the paired wires, for example, the L2 wire (5) and the shield (6). Here, two A communication devices (2) and two B communication devices (3) are connected here, but the number is not limited to this.

FIG. 2 is a diagram showing a cross-sectional structure of the shielded cable (1) with simplified conductors. A line impedance Z1 (7) constituted by a stray capacitance or the like exists between the L1 line (4), which is one of the pair lines, and the shield (6). The other line, L2 line (5), has a line impedance Z2 (8) consisting of the stray capacitance and the input impedance of the B communication device (3). Accordingly, there is an unbalance between the L1 line (4), the L2 line (5) and the shield (6). In this case, an unbalanced voltage Vub proportional to the ratio between the line impedance Z1 (7) and the line impedance Z2 (8) is generated as in the following equation (A).
Vub∝Vsignal × 20log (Z1 / Z2) (A)

  FIG. 3 is a graph showing the relationship between the frequency of the signal applied to the shielded cable (1) and the unbalanced voltage. The horizontal axis represents frequency [MHz], and the vertical axis represents voltage [V]. Here, the relationship is obtained by calculation assuming that the length of the transmission line is 100 m and the signal voltage is 1V.

  FIG. 4 is a diagram showing a configuration when a sine wave signal (voltage) is applied between the shield (6) and the L2 line (5). Here, the impedance (9) exists in the L2 line (5). When a voltage is applied in the configuration of FIG. 4, as shown in FIG. 3, an unbalanced voltage (Vc-in to Vd−) corresponding to the frequency is generated between the L1 line (4) and the L2 line (5) due to signal leakage. out) has occurred.

  FIG. 5 is a diagram illustrating a configuration when a sine wave signal is applied between the L1 line (4) and the L2 line (5). When a signal is applied in the configuration of FIG. 5, as shown in FIG. 3, an unbalanced voltage (Vd-in to Vc-out) corresponding to the frequency is generated between the shield (6) and the L2 line (5) due to signal leakage. ) Has occurred.

  FIG. 6 is a diagram showing an example of frequency spectrum characteristics of signals used for transmission of the A communication device (2) and the B communication device (3). Here, a signal related to an AMI (Alternate Mark Inversion) code (alternate mark inversion code) is transmitted between the A communication apparatuses (2), and an OFDM (Orthogonal Frequency Division Multiplexing) modulation scheme (orthogonal) is transmitted between the B communication apparatuses (3). It is assumed that a signal related to frequency division multiplexing is transmitted.

  As shown in FIG. 6, the signal of the AMI code related to the signal transmission of the A communication apparatus (2) has a wide band of n-order (n is an integer) harmonic component with a frequency half the bit rate as a fundamental wave. Has spread. Therefore, the harmonic component concerning the signal of A communication apparatus (2) is output to the frequency band which B communication apparatus (3) uses. Since this harmonic component acts as noise on the signal transmitted in the B communication device (3), Eb / No expressed by the ratio of the noise energy No to the signal energy Eb in one bit is deteriorated. However, since the B communication device (3) is connected between the shield (6) and the L2 line (5), the component generated as noise in the harmonic is shown in Vd-in to Vc-out in FIG. Thus, the voltage is about 1/10 of the signal voltage of 1V. Further, the harmonic component of the signal of the AMI code has a characteristic that the signal intensity decreases as the frequency increases (FIG. 6). Therefore, the noise applied to the B communication device (3) is actually low due to the influence of the signal of the AMI code.

  On the other hand, the OFDM signal related to the signal transmission of the B communication device (3) acts as noise on the signal of the AMI code related to the signal transmission of the A communication device (2), and deteriorates the Eb / No described above. However, since the A communication device (2) is connected between the L1 line (4) and the L2 line (5), the component generated as noise in the harmonics is represented by Vc-in to Vd-out in FIG. As shown, the maximum voltage is about 1/5 of the signal voltage of 1V. As the AMI code signal approaches the fundamental wave, the level of the component generated as noise decreases (FIG. 6). Therefore, the actually applied noise is very small. Therefore, the degree of mutual interference between the signals is low, and the occurrence of errors due to noise caused by the other signal is reduced.

  In addition, since the A communication device (2) and the B communication device (3) are connected between different lines, mutual input impedances do not directly affect each other. For example, consider a case where the B communication device (3) has a characteristic that the input impedance of the A communication device (2) is low in the frequency band used for signal transmission. At this time, if the A communication device (2) and the B communication device (3) perform signal transmission on the same line, the signal transmitted by the B communication device (3) is greatly attenuated. By connecting the A communication device (2) and the B communication device (3) between different lines in the shielded cable (1), such a state can be prevented. By using the shielded cable (1), it is possible to suppress the influence of the two types of communication devices on each other and perform signal transmission.

  As described above, according to the signal transmission system of the first embodiment, a shielded cable (1) having a pair of paired wires composed of L1 line (4) and L2 line (5) and a shield (6) as a conductor. ), A communication device that transmits one signal is connected via a paired wire, and a communication device that transmits the other signal is connected by one line of the paired wire and a shield so that the signal line is different and signal transmission is performed. Therefore, it is possible to perform signal transmission satisfactorily with less interference and the like. Further, by transmitting signals of different systems, interference and the like are further reduced. Therefore, two types of signal transmission can be performed only by the shielded cable (1) having a pair of pair wires.

Embodiment 2. FIG.
FIG. 7 is a diagram showing the relationship between the signal level (intensity) and the frequency according to the second embodiment of the present invention. In the first embodiment described above, the example in which the signal related to the transmission of the A communication device (2) and the signal related to the transmission of the B communication device (3) interfere with each other at some frequencies has been described. However, as shown in FIG. 7, if the frequency band fa of the signal related to the transmission of the A communication device (2) and the frequency band fb of the signal related to the transmission of the B communication device (3) are completely separated from each other. There is no direct influence from the mutually generated unbalanced voltages shown in FIG. In addition, since the A communication device (2) and the B communication device (3) are connected between different lines, mutual input impedances do not directly affect each other. Therefore, since the signal is not attenuated by other communication devices, two types of signal transmission can be performed with only the shielded cable (1) having a pair of paired wires in a good state.

Embodiment 3 FIG.
FIG. 8 is a diagram showing a method of performing signal relay of the B communication device (3) with input impedance provided in the A communication device (2). Although not particularly shown in the first embodiment, for example, one of the two B communication devices (3) is connected to the L1 line (4) and the shield (6), and the other is connected to the L2 line (5). It may be connected to the shield (6). In this case, signal transmission of the two B communication devices (3) cannot be performed. Therefore, in FIG. 8, the signal relay of the B communication device (3) is performed by the input impedance of the A communication device (2).

  For example, let us consider a case where the frequency band fa and the frequency band fb shown in FIG. 7 are the frequency bands of signals related to transmission of the A communication device (2) and the B communication device (3), respectively. For example, the capacitor has a lower impedance as the frequency is higher. Therefore, the frequency band fa is made sufficiently lower than the frequency band fb, and an element such as a capacitor that has a high impedance with respect to the frequency band fa is connected in parallel to the A communication device (2). Thereby, a low-impedance bypass path is formed by the element for the frequency band fb, and the signal of the B communication device (3) can be relayed to the L1 line (4) and the L2 line (5).

  For example, when the A communication device (2) performs signal transmission by baseband transmission at a basic frequency of 10 kHz, and the B communication device (3) performs signal transmission by a transmission method using a carrier (carrier wave) of 1 MHz, 0. The impedance of the 01 μF capacitor is about 1.6 kΩ for 10 kHz and about 16Ω for 1 MHz. Here, since the input impedance of the B communication apparatus (3) is generally configured to be several kΩ, it is considered that the signal can be relayed with almost no attenuation by the bypass path. Further, for example, when the high-frequency noise protection component of the A communication device (2) can act as an input impedance, the bypass path can be configured without any special elements.

  FIG. 9 is a diagram showing a method of performing signal relay by the repeater (10) connected between the paired L1 line (4) and L2 line (5). For example, when an input impedance is not provided in the A communication device (2), an independent repeater (10) is connected between the L1 line (4) and the L2 line (5), and the repeater (10 ) May be configured.

  In the above example, the case where the frequency band fa and the frequency band fb are the frequency bands of the signals related to the transmission of the A communication device (2) and the B communication device (3) has been described. Think about the opposite case.

  For example, when the A communication device (2) performs signal transmission by a transmission method using a carrier of 1 MHz, and the B communication device (3) performs signal transmission by baseband transmission at a fundamental frequency of 10 kHz, As an element to be formed, an inductor is connected in parallel to the A communication device (2) instead of a capacitor. For example, the impedance of a 330 μH inductor is about 20Ω for 10 kHz and about 2 kΩ for 1 MHz. Here, since the input impedance of the A communication apparatus (2) is generally configured to be several kΩ, it is considered that the signal can be relayed with almost no attenuation by the bypass path. Also, for example, when the B communication device (3) has a circuit system such as transformer coupling, the inductor of the primary winding can be used as the input impedance, and no bypass is provided without any special elements. A route can be configured.

  Here, an example of a frequency (band) for transmitting a signal has been described using 10 kHz and 1 MHz, but the present invention is not limited to this as long as a similar impedance relationship can be obtained at other frequencies. Furthermore, the bypass path has been described using the simplest capacitor or inductor as an example, but the input impedance may be configured using a circuit such as a filter that passes a predetermined frequency band, for example.

  As described above, according to the signal transmission system of the third embodiment, for example, one of the two B communication devices (3) is connected to the L1 line (4) and the shield (6), and the other device is L2. Even if it is connected to the line (5) and the shield (6), relaying can be performed using an element, circuit, or the like having different impedance depending on the frequency, so that the degree of freedom of connection of the communication device can be increased. .

Embodiment 4 FIG.
FIG. 10 is a diagram showing a configuration of a signal transmission system according to Embodiment 4 of the present invention. In FIG. 10, in addition to the A communication device (2) and the B communication device (3) described in the first embodiment, a set of C communication devices (11) that transmit signals having transmission methods different from those devices ( Hereinafter, the C communication device (11) is simply connected to the shielded cable (1). Here, the C communication apparatus (11) is shielded from a line (for example, L2 line (5)) different from one of the paired lines (for example, L1 line (4)) to which the B communication apparatus (3) is connected. (6) is connected so as to apply a signal represented by a voltage between them.

  FIG. 11 is a diagram illustrating an example of frequency spectrum characteristics and time axis signal waveforms of signals used for transmission of the A communication device (2), the B communication device (3), and the C communication device (11). Here, a signal related to the AMI code is transmitted between the A communication apparatuses (2). The B communication device (3) transmits a signal related to the OFDM modulation scheme. Further, the C communication device (11) transmits a signal related to a DS-SS (Direct Sequence Spread Spectrum) modulation method (direct spreading method).

  As shown in FIG. 11, the signal of the AMI code related to the signal transmission of the A communication device (2) has a wide band of n-order (n is an integer) harmonic component with a frequency half the bit rate as a fundamental wave. Has spread. Therefore, the harmonic component concerning the signal of A communication apparatus (2) is output to the frequency band which B communication apparatus (3) uses. Since this harmonic component acts as noise on the signal transmitted in the B communication device (3), Eb / No expressed by the ratio of the noise energy No to the signal energy Eb in one bit is deteriorated. However, the B communication device (3) is connected between the shield (6) and the L2 line (5), and the C communication device (11) is connected between the shield (6) and the L1 line (4). The component generated as noise in the wave becomes a voltage of about 1/10 with respect to the signal voltage of 1 V, as indicated by Vd-in to Vc-out in FIG. In addition, the harmonic component of the signal of the AMI code has a characteristic that the signal intensity decreases as the frequency increases. For this reason, the noise applied to the B communication device (3) is actually low due to the influence of the signal related to the AMI code. Further, since the C communication device (11) performs signal transmission in a higher frequency band than the B communication device (3), the influence of applied noise is considerably reduced.

  Further, the OFDM signal related to the signal transmission of the B communication device (3) and the DS-SS signal related to the signal transmission of the C communication device (11) are signals of the AMI code related to the signal transmission of the A communication device (2). It acts as a noise and worsens the above-mentioned Eb / No. However, since the A communication device (2) is connected between the L1 line (4) and the L2 line (5), the harmonic voltage generated as noise is as shown by Vc-in to Vd-out in FIG. In addition, it is reduced to about 1/5 at the maximum with respect to the signal voltage of 1V. Further, as the level of the fundamental wave of the AMI signal is approached, the level of the signal that becomes noise decreases, so the actually applied noise is very small.

  FIG. 12 shows an unbalanced voltage appearing between the L2 line (5) and the shield (6) when a sine wave signal (voltage) of 1V input is applied between the L1 line (4) and the shield (6). FIG. As for the interference between the B communication device (3) and the C communication device (11), the voltage generated as noise is 1 V signal voltage as shown by Vc1-in to Vc2-out in FIG. It is reduced to about 1/10, and the degree of signal interference is low. Therefore, the degree of mutual interference between the signals is low, and the occurrence of errors due to noise caused by the other signal is reduced.

  In addition, since the A communication device (2), the B communication device (3), and the C communication device (11) are connected between different lines, mutual input impedances do not directly affect each other. For example, consider a case where the B communication device (3) and the C communication device (11) have a characteristic that the input impedance of the A communication device (2) is low in the frequency band used for signal transmission. At this time, if the A communication device (2) and the B communication device (3) and / or the C communication device (11) perform signal transmission on the same line, the B communication device (3) and / or the C communication device ( 11) is greatly attenuated. By connecting the A communication device (2), the B communication device (3), and the C communication device (11) between different lines in the shielded cable (1), such a state can be prevented. . Then, by using the shielded cable (1), it is possible to suppress the influence of the three types of communication devices on each other and to transmit signals respectively.

  As described above, according to the signal transmission system of the fourth embodiment, the shielded cable (1) having the pair of paired wires composed of the L1 line (4) and the L2 line (5) and the shield (6) as a conductor. Thus, the communication device that transmits the first signal is connected by a pair wire, and the communication device that transmits the second signal is connected by one of the pair wires (for example, the L1 wire (4)) and the shield (6). In addition, since the communication device for transmitting the third signal is connected by the other wire (for example, the L2 wire (5)) and the shield (6) of the paired wires, there are three types only by the shielded cable (1). Signal transmission.

Embodiment 5. FIG.
FIG. 13 is a diagram showing the relationship between the signal level (intensity) and the frequency according to the fifth embodiment of the present invention. In the first embodiment described above, the signal related to the transmission of the A communication device (2), the signal related to the transmission of the B communication device (3), and the signal related to the transmission of the C communication device (11) are at some frequencies. An example of interference has been described. However, as shown in FIG. 12, the frequency band fa of the signal related to the transmission of the A communication device (2), the frequency band fb of the signal related to the transmission of the B communication device (3), and the transmission of the C communication device (11). If the frequency bands fc of such signals are completely separated from each other, there is no direct influence from the unbalanced voltage generated between them. Moreover, since the A communication device (2), the B communication device (3), and the C communication device (11) are connected between different lines, the mutual input impedances do not directly affect each other. Therefore, there is no occurrence of signal attenuation by other communication devices, so that three types of signal transmission can be performed with only a shielded cable (1) having a pair of paired wires in a good state.

Embodiment 6 FIG.
FIG. 14 is a diagram showing a configuration of a signal transmission system according to Embodiment 6 of the present invention. In the above-described embodiment, the shield (6) of the shielded cable (1) is used as a conductor, and a signal transmission is performed by connecting a communication device that transmits a signal of a different frequency band, method, etc. to the paired wire and the shield (6). Went. In the present embodiment, as shown in FIG. 14, instead of the shielded cable (1), for example, an electric wire (12) composed of three conductors such as a 3-core VVF is used, and for example, an earth wire in the electric wire (12) (13) is used as a conductor.

  In FIG. 14, A communication apparatus (2) is connected so that the signal represented by the voltage between the L1 line (4) and L2 line (5) which comprise an electric wire (12) may be applied. On the other hand, the B communication device (3) has a voltage between either the L1 line (4) or the L2 line (5) of the electric wire (12) (L2 line (5) in FIG. 14) and the ground line (13). It connects so that the signal represented by may be applied. The signal transmission and the like are the same as those in Embodiments 1 to 5 described above in which the shield (6) is replaced with the ground wire (13), and thus description thereof is omitted. Thus, if it is an electric wire (12) which has a conductor like an earth wire (13), a plurality of signal transmissions can be performed with less interference.

Embodiment 7 FIG.
FIG. 15 is a diagram showing a configuration of a signal transmission system according to Embodiment 7 of the present invention. In this embodiment, as shown in FIG. 15, instead of the shielded cable (1) or the like, a pair of pair wires (14) composed of two conductive wires and a grounding ground wire (15) are used as conductors.

  In FIG. 15, the A communication device (2) is connected to apply a signal represented by a voltage between the L1 line (4) and the L2 line (5) constituting the pair line (14). . On the other hand, the B communication device (3) is connected between either the L1 line (4) or the L2 line (5) of the pair line (14) (the L2 line (5) in FIG. 15) and the ground wire (15). It connects so that the signal represented by the voltage of may be applied. The signal transmission and the like are the same as those in Embodiments 1 to 5 described above, in which the shield (6) is replaced with the ground wire (15), and thus the description thereof is omitted. Thus, if a conductor like the grounding ground wire (15) is provided in the pair wire (14), a plurality of signal transmissions can be performed with less interference.

Embodiment 8 FIG.
FIG. 16 is a diagram showing a configuration of a signal transmission system according to Embodiment 8 of the present invention. In the present embodiment, as shown in FIG. 16, instead of the shielded cable (1) or the like, a pair of pair wires (14) composed of two conducting wires and a metal structure (16) such as a steel frame of a building. Is used as a conductor.

  In FIG. 16, the A communication device (2) is connected so as to apply a signal represented by a voltage between the L1 line (4) and the L2 line (5) constituting the pair line (14). . On the other hand, the B communication device (3) has either the L1 line (4) or the L2 line (5) of the pair line (14) (L2 line (5) in FIG. 16) and the metal structure (16). It is connected to apply a signal represented by a voltage between them. The signal transmission and the like are the same as those in Embodiments 1 to 5 described above in which the shield (6) is replaced with the metal structure (16), and thus description thereof is omitted. Thus, if a conductor like the metal structure (16) is provided on the pair wire (14), a plurality of signal transmissions can be performed with less interference.

Embodiment 9 FIG.
FIG. 17 is a diagram showing a configuration of a signal transmission system according to Embodiment 9 of the present invention. In the present embodiment, as shown in FIG. 17, instead of the shielded cable (1) or the like, a pair of pair wires (14) composed of two conductive wires and a metal pipe (17 such as a refrigerant pipe of an air conditioner) ) As a conductor. For example, the A communication device (2) and the B communication device (3) may be an outdoor unit, an indoor unit, or the like in the air conditioner.

  In FIG. 17, the A communication device (2) is connected so as to apply a signal represented by a voltage between the L1 line (4) and the L2 line (5) constituting the pair line (14). . On the other hand, the B communication device (3) is connected between the L1 line (4) or the L2 line (5) of the pair line (14) (L2 line (5) in FIG. 17) and the metal pipe (17). It is connected to apply a signal represented by a voltage. The signal transmission and the like are the same as those in Embodiments 1 to 5 described above in which the shield (6) is replaced with the metal pipe (17), and thus description thereof is omitted. Thus, if a conductor such as a metal pipe (17) is provided on the pair wire (14), a plurality of signal transmissions can be performed with less interference.

Embodiment 10 FIG.
In the above-described embodiment, the AMI code is used for the signal of the A communication device (2), the OFDM is used for the signal of the B communication device (3), and the DS-SS is used for the signal of the C communication device (11). However, the present invention is not limited to this. For example, other signal systems such as PSK, FSK or ASK, or NRZ, RZ, CMI modulation may be used. Further, although each communication apparatus has been described using different signal systems, the same or a part of the same signal system may be used, and mutual signal interference can be reduced.

It is the figure which showed the structure of the signal transmission system which concerns on Embodiment 1 of this invention. It is the figure which showed the cross-section of the shield cable (1). It is a figure showing the relationship between the frequency of a signal and an unbalanced voltage. It is a figure showing the structure which applies a signal between a shield (6) and L2 line (5). It is a figure showing the structure which applies a signal between L1 line (4) and L2 line (5). It is a figure which shows the frequency spectrum characteristic example of a signal. It is a figure showing the relationship between the signal level and frequency which concern on Embodiment 2. FIG. It is the figure which showed the method of relaying by the input impedance of A communication apparatus (2). It is the figure which showed the method of relaying using a repeater (10). It is the figure which showed the structure of the signal transmission system which concerns on Embodiment 1 of this invention. It is a figure which shows the frequency spectrum characteristic example of a signal. It is a figure showing the relationship between the frequency of a signal and an unbalanced voltage. It is a figure showing the relationship between the signal level which concerns on Embodiment 5, and a frequency. It is the figure which showed the structure of the transmission system which concerns on Embodiment 6 of this invention. It is the figure which showed the structure of the transmission system which concerns on Embodiment 7 of this invention. It is the figure which showed the structure of the transmission system which concerns on Embodiment 8 of this invention. It is the figure which showed the structure of the transmission system which concerns on Embodiment 9 of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Shield cable, 2 A communication apparatus, 3 B communication apparatus, 4 L1 line, 5 L2 line, 6 Shield, 7 Line impedance Z1, 8 Line impedance Z2, 9 Impedance Z, 10 Repeater, 11 C communication apparatus, 12 Electric wire , 13 Ground wire, 14 Pair wire, 15 Ground wire, 16 Metal structure, 17 Metal piping.

Claims (13)

A pair of two conductive wires;
A set of first communication devices that are connected to the pair wires and perform signal transmission using the pair wires;
A signal transmission system comprising: a pair of second communication devices that are connected to one of the paired wires and a conductor and perform signal transmission using the one line and the conductor. A pair of paired wires comprising a first line and a second line;
A set of first communication devices that are connected to the pair wires and perform signal transmission using the pair wires;
A set of second communication devices connected to the first line and the conductor, and performing signal transmission using the first line and the conductor; and connected to the second line and the conductor; A signal transmission system comprising: a third set of communication devices that perform signal transmission using two wires and a conductor.   3. The signal transmission system according to claim 1, wherein the frequency of signals transmitted by each set of communication devices is different from each other. A pair of two conductive wires;
A set of first communication devices that are connected to the pair lines and perform signal transmission in a first frequency band using the pair lines;
And a pair of second communication devices that are connected to one of the pair wires and a conductor, and perform signal transmission in a second frequency band using the one line and the conductor. Signal transmission system.   5. The signal transmission system according to claim 4, wherein the first frequency band and the second frequency band do not overlap.   6. The signal according to claim 4, wherein the paired wires are connected and relayed by an impedance element having high impedance in the first frequency band and low impedance in the second frequency band. Transmission system.   The signal transmission system according to claim 6, wherein the pair wires are coupled by an internal impedance of the first communication device.   The signal transmission system according to any one of claims 1 to 7, wherein systems of signals transmitted by each set of communication devices are different from each other.   The signal transmission system according to claim 1, wherein the pair wire is a pair wire with a shield, and the conductor is the shield.   The signal transmission system according to claim 1, wherein the pair wire is a three-wire wiring having a ground wire, and the conductor is the ground wire.   The signal transmission system according to claim 1, wherein the conductor is a ground wire.   The signal transmission system according to claim 1, wherein the conductor is a metal structure.   The signal transmission system according to claim 1, wherein the conductor is a metal pipe.

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