JP3078498B2 - Signal transmission interface unit and signal transmission network using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[Object of the Invention]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal transmission interface unit and a network using the same, and more particularly to a signal transmission line using a coaxial cable installed in a general house, apartment house, office, or the like. The present invention relates to a device for inputting and outputting a high-frequency signal to and from a device.

[0002]

2. Description of the Related Art Conventionally, as an interface unit for guiding a high-frequency signal from a signal transmission line using a coaxial cable to an electronic device, a series unit for a TV signal, which is frequently used in a TV common reception facility in an apartment house, is used. It is typical. The system and equipment used will be described with reference to FIG.

FIG. 9 shows an outline of a conventional TV common reception facility in a common house using a large number of serial units for TV signals. In FIG. 9, 1-1,1-
2, 1-3, 1-4 are antenna groups for receiving a TV signal.
Among them, 1-1 and 1-2 indicate SHF band parabolic antennas for receiving BS and CS, and the remaining 1-3 indicate V-band antennas.
Antennas for receiving terrestrial waves in the HF band, and 1-4 for receiving terrestrial waves in the UHF band. Each TV signal received by these antennas is transmitted through coaxial cables 4-1, 4-
It is introduced into the mixer 2-1 via 2,4-3,4-4.

In this receiving equipment, the output of the mixer 2-1 is guided to the input of the amplifier 3 by a coaxial cable, and
, And then enters the input of the distributor 2-2. The distributor 2-2 is an example of a four-way distributor.
The TV signal divided into four equals is output from the distributor 2-2 through the coaxial cables 5, 6, 7, and 8 in which the serial units are connected in multiple stages.
... 6-1, 6-2, ... 7-1, 7-2, ... 8-1,8-
, And are distributed to each TV viewer through these branch terminals.

In this case, each antenna, a mixer, an amplifier,
Since the one with the distributor has the characteristic of a terminal, these are generally called a head end.

The features of such a conventional TV joint reception system are as follows. The headend system is centralized in one place on the system. 2. The flow of the TV signal is a one-way flow from the head end to the line down direction. 3. Signals from the subscriber are not transmitted directly to other subscribers without going through the headend. That is.

Here, the details of the conventional serial unit, which is an interface unit, will be described in detail. A part of a high-frequency signal input from an input terminal is electrically branched using a directional coupler. , And the rest is transmitted as it is to the output side. On the other hand, the high-frequency signal entering from the output terminal side is transmitted to the input side, but is not coupled to the branch terminal.
It is a so-called hybrid circuit.

FIG. 10 shows an outline of the structure. In FIG. 10, reference numeral 1 denotes an input terminal. An inner conductor of a coaxial cable is connected to a terminal insulated from the metal cover 4, and a high-frequency signal is placed inside the housing. It serves as a guide. The outer conductor of the cable on the input side is structured to be grounded to the housing by a metal fitting 5 below the terminal 1. Similarly, the output terminal is hidden in the figure, but is attached to the side of the housing opposite to the terminal 1 in the same manner as the terminal 1.

The branch terminal 2 is taken out by a connector with the internal conductor insulated from the surface of the front metal plate 3. The front metal plate is wired by embedding this series unit in, for example, a wall in a living room of a house, and the branch terminal is installed so as to be exposed from the wall surface into the living room. For this reason, a screw hole 6 of a specified size for attachment to an electric wire box and a hole 7 for attaching a decorative plate on the front surface of the branch terminal are generally clear for aesthetic reasons.

As described above, the conventional series unit is a device using the directional coupler, and the high-frequency signal from the input terminal is forward-coupled to the branch terminal with an appropriate amount of attenuation.
The receiver is connected, but the signal from the output terminal is designed so as not to appear at the branch terminal as much as possible by utilizing the reverse coupling of the directional coupler. This is because T is located on the downstream side of the series unit, that is, on the side opposite to the antenna.
This is a result of consideration so that noise generated from V does not flow.

[0011]

As described above, the conventional serial unit cannot directly transmit a signal from the downstream side of the serial unit to the branch terminal.
Therefore, if a signal from the downstream side is to be transmitted to each branch terminal, the signal must be once transmitted to the head end, transmitted again to the downstream line, and extracted from the branch terminal.

[0012] This means that if the same frequency band as that of the uplink is already present on the downlink, the frequency of the uplink, that is, the frequency of the antenna at the head end is not duplicated with the frequency of the existing downlink. , And a frequency converter for that purpose is required.

Further, in the conventional system, the equipment for transmitting a signal must be centrally installed at one location of the head end. For example, when the head end is placed near an antenna installed on a rooftop, an underground Cable T coming from
The coaxial cable for V had the inconvenience that it had to be transmitted to the roof with the headend once.

The present invention has been made in view of the above points, and provides a signal transmission interface unit capable of flowing a signal in both forward and backward directions of a line, and a signal transmission network using the same. It is intended for. [Configuration of the Invention]

[0015]

To achieve the above object, according to the present invention, there is provided a trunk line, an input terminal and an output terminal provided on the trunk line, and first and second terminals connected to the trunk line. And a first and a second directional coupler connected in reverse series with each other, wherein the first branch terminal is arranged in a direction from the input terminal to the output terminal. The second branch terminal is forward-coupled to the high-frequency signal flowing in the direction from the output terminal to the input terminal, and is reverse-coupled to the high-frequency signal flowing in the opposite direction. 3. The signal transmission interface unit according to claim 2, wherein the signal transmission interface unit is connected so as to be reversely coupled to a high-frequency signal flowing in the direction. 2 with terminals and, and a branch terminal sequentially coupled to said input terminal and reverse coupled to said output terminal, respectively
In a signal transmission interface unit comprising two directional couplers connected in reverse series and inserted between the input terminal and the output terminal, and the branch terminal connected to a coupling terminal for signal injection, the input terminal and the output An interface unit main body in which a switch is provided between a terminal and each of the directional couplers; and an absorbing unit, wherein the switch is opened by being combined with the main body of the interface unit to open the input terminal and the output. A signal transmission interface unit comprising an adapter for connecting the absorption resistor to a terminal, and a signal formed by connecting a plurality of the signal transmission interface units according to claim 1 or 2 in series. A line is formed, and a branch terminal of any of the signal transmission interface units is formed. And a signal transmission network having a branch terminal through which a signal propagates in the signal line in a direction opposite to a direction in which a signal flows from the network input terminal. is there.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, an interface unit for a coaxial cable has an external appearance and a circuit configuration.
It has two main terminals 1-1 and 1-2 as input and output terminals, and two coupling terminals 2-1 and 2-2 as signal injection terminals coupled to each input terminal.

That is, the high-frequency signal supplied from the trunk terminal 1-1 enters the input terminal of the directional coupler 3-1 and a part of the signal is transmitted from the branch terminal of the directional coupler 3-1 to the coupling terminal 2. -1 and the remainder is transmitted to the trunk terminal 1-2 through the directional coupler 3-2. However, the main terminal 1-1
A high-frequency signal coming from the directional coupler 3-2 is a so-called directional coupler that is not coupled to the branch terminal of the directional coupler 3-2 even if it enters the directional coupler 3-2.

The high-frequency signal supplied from the trunk terminal 1-2 enters the directional coupler 3-2, a part of which is coupled to the coupling terminal 2-2, and the rest is directly coupled to the trunk terminal 1-1. It is transmitted, but hardly coupled to the coupling terminal 2-1 of the directional coupler 3-1. In other words, the circuit configuration of this unit may be considered as two back-to-back directional couplers.

The interface unit having such a circuit configuration has a structure shown in FIG. That is,
In FIG. 1A, reference numeral 1-1 denotes a trunk terminal, which is a terminal insulated from the metal housing cover 4 and connected to an inner conductor of a coaxial cable, and serves to guide a high-frequency signal into the housing. The outer conductor of this cable is structured to be grounded to the housing by a metal fitting 5 below the terminal 1-1. Similarly,
Although the other trunk terminal is hidden in the figure, it is attached to the side of the housing opposite to the terminal 1 as the trunk terminal 1-2 in the same manner as the terminal 1-1.

The branch terminal 2-1 is taken out by a connector on the surface of the front metal plate 3 with its internal conductor insulated. Similarly, a branch terminal 2 corresponding to the trunk terminal 1-2.
-2 is also taken out from the surface of the front metal plate 3 by a connector with its internal conductor insulated. The front metal plate is provided with, for example, a screw hole of a specified size for mounting to an electric wire box, and a decorative plate on a surface of a branch terminal exposed to the room so that the interface unit can be easily installed in a wall of the room. The holes for attaching the horns are clear.

FIG. 2 shows a configuration of a receiving facility using such an interface unit as a component of a TV common receiving facility. FIG. 2 shows a basic TV co-listening system configured using an interface unit.
2, 3, and 4 are interface units.

Each interface unit 1, 2, 3, 4
In FIG. 1, the connection terminal on the upper side of the paper is a counterclockwise connection terminal, and is a CCW (Counter Clockwise) terminal for short. In addition, the coupling terminal on the lower side of the paper is a clockwise branch terminal,
For simplicity, it will be referred to as a CW (Clockwise) terminal. Then, for convenience, the trunk terminal that is forward-coupled to the CCW terminal is referred to as TA.
A terminal that is forward-coupled to the trunk terminal and the CW terminal will be referred to as a TB trunk terminal. Then, on the line, the TA trunk terminal coupled to the CCW terminal is always connected to the TB trunk terminal coupled to the CW terminal when the next connection is made. Hereinafter, such a connection order is repeated until a predetermined number of interface units are connected.

Now, in FIG. 2, the antennas 9-1, 9
-2, 9-3, 9-4, VHF, UHF, S
Each HF television wave is mixed by the mixer 8, converted into a high-frequency signal of a required level by the amplifier 6, and supplied to the CCW terminal of the interface unit 1. This signal appears at the TA main terminal of the interface unit 1, flows counterclockwise through the coaxial cable 10, forms a CCW line, and is absorbed by the absorption resistance Ra of the circulator 5-1.

The connection is connected to the CW terminals of the interface units 3, 4 and 2 connected to the cable 10. Therefore, a TV receiver can be connected to these terminals to receive an image. On the other hand, the signal from the VTR 7 supplied to the CW terminal of the interface unit 4 appears at the TB trunk terminal of the interface unit and flows clockwise through the coaxial cable 10 to form a CW line and to the absorption resistor Ra of the circulator 5-2. Absorbed.

The space between them is coupled to the CCW terminals of the interface units 3, 1 and 2 connected to the cable 10. Therefore, a VTR monitor receiver can be connected to these terminals. That is, the signal input from the CCW terminal of the interface unit appears at the CW terminal of each interface unit, and the signal input to the CW terminal appears at the CCW terminal. And C
Since both CW and CW lines are terminated by the absorption resistor Ra connected to the absorption terminal of the circulator, there is no reflection on the lines.

(Embodiment 1) Next, an embodiment of the interface of the present invention configured as a simple line system like the conventional example shown in FIG. 9 will be described with reference to FIG.

In FIG. 3, reference numerals 1, 2, 3, and 4 indicate interface units of the present invention. In FIG. 3, the antenna 9- is connected to the CW terminal of the interface unit 1.
VHF, UH received at 1, 9-2, 9-3, 9-4
The television waves of F and SHF are mixed by the mixer 8 and set to a required level by the amplifier 6 and supplied. This signal passes through the interface units 2 and 3 and enters from the TA trunk terminal of the interface unit 4, and the other T
It is terminated by being absorbed by the absorption resistor Ra connected to the B main terminal. Meanwhile, these signals can be taken out from the CCW terminals of the interface units 2 and 3 as branch outputs.

The CCW of the interface unit 4
The high frequency signal from the VTR supplied to the terminal passes through the interface units 3 and 2 and enters the interface unit 1 from the TB trunk terminal, and is terminated by being absorbed by the absorption resistor Ra connected to the other TA trunk terminal. Is done. Meanwhile, this signal can be taken out as a branch output from the CW terminals of the interface units 2 and 3.

As described above, the interface unit of the present invention can be provided with a plurality of interface units in the middle of a coaxial cable transmission line by wiring a coaxial cable in a loop or a single line. Are sequentially connected, an interface unit serves as an interface unit for supplying a high-frequency signal from a signal source to the line, and an interface unit having the same structure serves to branch and output a signal from the line.

Therefore, it is not necessary to fix the so-called head end at one place, and power may be supplied to an interface unit at any position in the line, and two lines of a CCW line and a CW line are connected to one cable. Can be provided. Therefore, the bandwidth of the line is substantially doubled, and a broadband coaxial line can be constructed economically.

In the above-described example, the TV signal and the VTR signal have been described. However, the signals are not limited to these, and a high-frequency signal for remotely controlling a device, an interphone, a remote monitor, a telephone, etc. It is needless to say that the high-frequency signal can be used by being superimposed.

[0032]

Returning again to FIG. 1, FIGS. 1 (a) and 1 (b)
Shows an example of the interface unit. First, in FIG. 1A, the chassis 3 is a stainless steel plate having a thickness of 1.0 mm and a width of about 42 mm.
Insulation tables 6-1 and 6-2 are attached to the front surface. Then, connectors 2-1 and 2-2 serving as coupling terminals are disposed substantially at the center of the insulator, and outer conductors of the connectors are electrically connected to the chassis 3, and the center conductor is housed in the chassis. Is connected to the branch terminal of the directional coupler. Here, 2-1 is used as a CCW terminal and 2-2 is used as a CW terminal.

The directional coupler circuit is fixed in an appropriate manner inside the chassis 3, but the main terminal is provided on the side of the cover 4 which is put on to protect the directional coupler circuit.
As the TA trunk terminal 1-1 and the TB trunk terminal 1-2,
Connected to internal directional coupler. The cover 4
It is made of a 0.6 mm thick stainless steel plate and is fixed to the chassis 4.

FIG. 1B is a view for explaining the electrical connection, wherein 1-1 indicates a TA trunk terminal and 1-2 indicates a TB trunk terminal. Reference numeral 2-1 denotes a CCW terminal connected to a branch output of the directional coupler 3-1. Reference numeral 2-2 denotes a CW terminal connected to a branch output of the directional coupler 3-2.

Embodiment 2 FIGS. 4A and 4B show another embodiment of the present invention. The main configuration is the same as the configuration in FIG.
In the second embodiment, there are provided sub terminals 7-1 and 7-2 for directly drawing out the signal flowing through the trunk terminal to the front surface. In FIG. 4A, the chassis 3 has a thickness of 1.0 mm,
A stainless steel plate having a width of about 42 mm, insulating bases 6-1 and 6-2 are mounted on the front surface thereof, and connectors 2-1 and 2-2 serving as coupling terminals are provided at substantially the center of the insulator. The conductors are electrically connected to the chassis 3, and the center conductor is connected to the branch terminals of the respective directional couplers housed in the chassis. Here, 2-1 is used as a CCW terminal and 2-2 is used as a CW terminal. Further, holes reaching the inside of the chassis as sub terminals 7-1 and 7-2 penetrate through the insulating tables 6-1 and 6-2.

The directional coupler circuit is fixed inside the chassis 3, and the trunk terminal is provided on the side of the cover 4 covered for protecting the directional coupler circuit.
-1, TB trunk terminal 1-2 connected to an internal directional coupler. The cover 4 is made of a 0.6 mm thick stainless steel plate and is fixed to the chassis 4.

FIG. 4B is a diagram for explaining the electrical connection, wherein 1-1 indicates a TA trunk terminal and 1-2 indicates a TB trunk terminal. Reference numeral 2-1 denotes a CCW terminal connected to a branch output of the directional coupler 3-1. Reference numeral 2-2 denotes a CW terminal connected to a branch output of the directional coupler 3-2. Further, the switches 8-1 and 8-2 are connected to the sub terminals 7-1 and 7-2.
Is arranged at a position corresponding to. These switches 8-
1, 8-2 are effective when a high-frequency device is further mounted on the front surface of the interface unit of the present invention.

FIG. 5 shows an example in which an adapter for attaching an absorption resistor is attached in the system shown in FIG. 3 with its structure deformed for easy understanding. Here, by connecting the adapter to the interface unit, the conductive trunk pins 10-1 and 10-2 enter the unit, and then press the switches 8-1 and 8-2 to thereby connect the trunk terminals TA and The signal from the trunk terminal TB is blocked from being transmitted to the directional coupler in the unit, introduced into the adapter by the conductive trunk pins 10-1 and 10-2, and absorbed by the absorption resistor Ra.

FIG. 5 is not necessarily the structure of the interface unit of the present invention shown in FIG. 4, but shows the same operation. As shown in FIG. 5, although the circuit contents of the adapter 9 differ depending on the purpose, when the adapter is mounted, the trunk line signal is output into the adapter by the conductive trunk pins 10-1 and 10-2 coming out of the adapter. This is an operation to be introduced.

The configuration in which a switch is incorporated in the interface unit of the present invention is also effective when, for example, the circulator shown in FIG. 2 is attached.

(Embodiment 3) FIGS. 6A and 6B show still another embodiment of the interface unit of the present invention. In FIG. 6A, the chassis 3 is a stainless steel plate having a thickness of 1.0 mm and a width of about 42 mm.
Insulating bases 6-1 and 6-2 are attached to the front surface thereof.
The outer conductor of this connector is electrically connected to the chassis 3 and the center conductor is connected so as to take out a branch output from each directional coupler housed in the chassis. .

Here, 2-1 is a CCW terminal and 2-2 is a CW terminal.
Used as W terminal. The directional coupler circuit is fixed in a suitable manner inside the chassis 3, but the main terminals are covered by a cover 4 to protect the directional coupler circuit.
Are connected to an internal directional coupler as a TA trunk terminal 1-1 and a TB trunk terminal 1-2. Cover 4
Is made of a 0.6 mm thick stainless steel plate and is fixed to the chassis 4.

FIG. 6B is a diagram for explaining the electrical connection, wherein 1-1 indicates a TA trunk terminal and 1-2 indicates a TB trunk terminal. The TA trunk terminal and the TB trunk terminal are connected by a choke coil 11. The choke coil was manufactured by tightly winding an insulated copper wire having a diameter of 0.6 mm ten times around a NiZn ferrite bar having a diameter of 5 mm and a length of 10 mm.

Further, the TA trunk terminal and the directional coupler 3-
1 is connected through a capacitor 12-1, and the TB trunk terminal and the directional coupler 3-2 are connected through a capacitor 12-2. Further, the CCW terminal and the directional coupler 3-1 are connected through a capacitor 12-3, and 2-1 is a CCW terminal connected to a branch output of the directional coupler 3-1. This is a CW terminal connected to the branch output of the directional coupler 3-2.

Since the interface unit of the present invention having such a circuit configuration can supply a commercial frequency or DC power supply by superimposing a high-frequency signal on the main line, power can be supplied to an amplifier arranged in the main line. it can.

Power is supplied from the CCW terminal to the trunk through the choke coil 13 shown in FIG.
Power can be supplied from the main line. Therefore, for example, power for driving a low noise amplifier or a block converter can be supplied from the coupling terminal side.

Each of the first to third embodiments has a directional coupler therein. As the directional coupler used in the present invention, well-known distributed line type directional couplers may be used, but these do not always have wideband characteristics. Therefore, here, a high-frequency transformer type directional coupler using a magnetic material is used.

FIG. 7 shows an example of this high-frequency transformer type directional coupler. T in the figure is a high-frequency transformer having a turn ratio of 1: 3. Actually, it is wound around a toroidal core made of NiZn ferrite having an outer diameter of 4 mm, an inner diameter of 2 mm, and a thickness of 2 mm.

For example, the primary winding is wound once by penetrating the inner diameter of the toroidal core, and the secondary winding is wound three times. In this case, the primary to secondary winding ratio is 1: 3. Assuming that two completely similar high-frequency transformers are used and connected as shown in FIG. 7 and each terminal is terminated with a characteristic impedance. The signal from the terminal 1 is transmitted to the terminal 2 with a loss of about 0.5 dB. 2. The signal from the terminal 1 is transmitted to the terminal 3 with a loss of about 10 dB. 3. The signal from the terminal 1 has a loss of about 30 dB at the terminal 4 and is not transmitted.

As is apparent from the figure, the directional coupler is a symmetrical circuit. The signal from the terminal 2 is transmitted to the terminal 1 with a loss of about 0.5 dB. 2. The signal from the terminal 2 is transmitted to the terminal 4 with a loss of about 10 dB. 3. The signal from the terminal 2 is not transmitted because a loss of about 30 dB occurs at the terminal 3. A so-called directional coupler having the characteristic described above can be obtained.

In the present invention, the directional coupler shown in FIG. 7 may be used as a TA trunk terminal, terminal 2 as a TB trunk terminal, terminal 3 as a CCW terminal, and terminal 4 as a CW terminal. Depending on the state of the device connected to the terminal 4 with respect to the signal input from the terminal, the matching of the terminal 3 may not always be perfect, and at the same time, the same reason may be applied to the signal input from the CW terminal. Therefore, the terminal 3 is not always in the terminal state.

FIG. 8 shows an embodiment in which anti-reflection measures are taken. In this embodiment, as shown in FIG.
The circuit of FIG. 7 is back-to-back, and is provided separately as a directional coupler for the CCW terminal and a directional coupler for the CW terminal.

[0054]

As described above, according to the present invention, a signal is transmitted from an electronic device to a transmission line on a coaxial cable installed in an ordinary house, apartment house, office, or the like. Since the signal flowing through the trunk is guided to the electronic device, it is possible to use the signal flowing from any trunk terminal side of the interface unit, and to separate and supply the signal to both trunks.

The interface unit of the present invention having such a function not only doubles the usable frequency band as compared with the conventional network, but also fixes the head end to the forefront of the signal transmission line. Without having to install the interface unit anywhere on the track, signals can be supplied to it. In addition, headends can be installed at a plurality of locations. For example, by laying out lines in a line, more reasonable and economical signal transmission equipment can be constructed.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a signal transmission interface unit, FIG. 1 (a) is an external view, and FIG. 1 (b) is a connection diagram.

FIG. 2 is a conceptual diagram showing an example of a TV co-listening system using the signal transmission interface unit of FIG. 1;

FIG. 3 is a conceptual diagram showing one embodiment of a TV co-listening system according to the present invention using the signal transmission interface unit of FIG. 1;

FIG. 4 is a diagram showing another embodiment of the signal transmission interface unit of the present invention. FIG. 4 (a) is an external view, FIG.
(B) is a connection diagram.

FIG. 5 is a diagram showing a situation where an adapter is attached to the interface unit of FIG. 4;

6A and 6B are diagrams showing still another embodiment of the signal transmission interface unit of the present invention, wherein FIG. 6A is an external view and FIG. 6B is a connection diagram.

FIG. 7 is a diagram illustrating a directional coupler used in the signal transmission interface unit of the present invention.

FIG. 8 is a diagram illustrating a combination of directional couplers used in the signal transmission interface unit of the present invention.

FIG. 9 is a conceptual diagram showing an example of the configuration of a conventional TV co-listening system.

10A and 10B are diagrams illustrating a serial unit used in a conventional TV co-listening system, wherein FIG. 10A is an external view and FIG. 10B is a connection diagram.

[Explanation of symbols]

TA Main line for constructing a counterclockwise line TB Main line for constructing a clockwise line CCW Counterclockwise line CW Clockwise line T High frequency transformer 1-1 For constructing a counterclockwise line Trunk terminal 1-2 Trunk terminal for constructing a clockwise circuit 2-1 Coupling terminal for constructing a counterclockwise circuit 2-2 Coupling terminal for constructing a counterclockwise circuit 3-1 Counter Directional coupler for constructing clockwise line 3-2 Directional coupler for constructing clockwise line

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-50-93534 (JP, A) JP-A-9-83830 (JP, A) JP-A-61-150480 (JP, A) JP-A-62 24778 (JP, A) JP-A-62-128687 (JP, A) JP-A-8-307188 (JP, A) JP-A-7-25657 (JP, U) JP-A-3-98566 (JP, U) (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 5/00 H04N 7/10 H04N 7/16 H04L 13/00

Claims (3)

(57) [Claims] A first and a second branch terminal coupled to the main line, the input terminal and the output terminal provided on the main line, and the first and second branch terminals connected in reverse series to each other; In the signal transmission interface unit having the directional coupler of the above, the first branch terminal is forward-coupled to a high-frequency signal flowing from the input terminal to the output terminal, and is opposite to a high-frequency signal flowing in the reverse direction. The second branch terminal is connected so as to be forward-coupled to a high-frequency signal flowing from the output terminal to the input terminal, and to be reverse-coupled to a high-frequency signal flowing in the opposite direction. Interface unit for signal transmission. 2. An anti-serial connection of two directional couplers each having a main line, an input terminal and an output terminal provided on the main line, and a branch terminal which is forward-coupled to the input terminal and reverse-coupled to the output terminal. In the signal transmission interface unit connected and inserted between the input terminal and the output terminal and connecting the branch terminal to a coupling terminal for signal injection, the input terminal and the output terminal and the directional coupler An interface unit main body provided with a switch between each of the interface units; and an absorption resistor, wherein the switch is opened by being combined with the interface unit main body, and the absorption resistor is connected to the input terminal and the output terminal. An interface unit for signal transmission, comprising an adapter. 3. A signal line is formed by connecting a plurality of signal transmission interface units according to claim 1 or 2 in series, and one of the branch terminals in one of the signal transmission interface units is used as a network input terminal. A signal transmission network in which a branch terminal through which a signal propagates in the signal line in a direction opposite to a direction in which a signal flows from the network input terminal is used as a network output terminal.