JP2001061134A - Transmission signal amplifier and bidirectional CATV system - Google Patents

Abstract

(57) [Problem] To improve the attenuation rate of noise transmitted in a state in which signal transmission is prohibited, and to match impedance before and after an input terminal and an output terminal of a transmission signal amplifier. When a transmission of an uplink signal is prohibited, a control circuit issues a command to an intermittent circuit to input a signal to an input terminal.
The transmission path in the device from 1 to the output terminal T2 is disconnected. The control circuit 19 also issues a command to the power supply cutoff circuits 15 and 17, and the power supply cutoff circuits 15 and 17 cut off the supply of operating power from the power supply circuit to the amplifier circuits 11 and 13 according to the command. Further, the control circuit 19 also issues a command to the input-side ground switching circuit 25 and the output-side ground switching circuit 29. The input-side ground switching circuit 25 grounds the input terminal T1 via the resistor 23 according to the command, and The ground switching circuit 29 grounds the output terminal T2 via the resistor 27 according to this command.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bidirectional CATV system in which a center device and a terminal device are connected via a CATV transmission line so that an uplink signal can be transmitted from the terminal device to the center device. And a transmission signal amplifier for amplifying an upstream signal transmitted from a terminal device to a center device.

[0002]

2. Description of the Related Art Conventionally, a center device and a terminal terminal are connected via a CATV transmission line, and an upward signal is transmitted from a terminal device (such as a personal computer) connected to the terminal terminal to a center device (head end). Possible bidirectional CA
In a TV system, an upstream signal input to a CATV transmission line from a terminal is usually amplified and transmitted by a transmission signal amplifier (upstream signal amplifier) provided on the CATV transmission line. The transmission signal amplifier is installed independently as a bidirectional amplifier in which an upstream signal amplifier and a downstream signal amplifier are combined,
Some are built into branch amplifiers and extension amplifiers.

[0003] By the way, the downstream signal (television broadcast signal) transmitted from the center device to the terminal terminal is transmitted almost continuously, but the upstream signal transmitted from the terminal terminal to the center device is transmitted. Transmitted intermittently as needed. For this reason, a technique has been proposed in which the transmission signal amplifier prohibits transmission of the uplink signal during a period in which the uplink signal is not transmitted so that noise is not transmitted. FIG. 3 is a block diagram for explaining the configuration of a conventional transmission signal amplifier (uplink signal amplifier).
FIG. 3 shows a state in which transmission of an uplink signal (noise) is prohibited.

[0004] As shown in FIG.
Reference numeral 0 denotes an input terminal T1, an output terminal T2, an amplifier circuit 81, a switch circuit 83, an amplifier circuit 85, a resistor 87, a resistor 89, and a control circuit 91. The control circuit 91 controls the connection state of the switch circuit 83. By doing so, the transmission / reception of the transmission of the uplink signal is switched. The control circuit 91
Operate in response to a command from the center device.

More specifically, when the transmission of the upstream signal is permitted, the contact point P1 and the contact point P2 constituting the switching circuit 83 are connected, and the contact point P4 and the contact point P5 are connected. The input terminal T1 and the output terminal T2 are connected via 81 and 85. Then, the upstream signal input from the input terminal T1 is amplified by the amplifier circuits 81 and 85 and output from the output terminal T2.

On the other hand, when the transmission of the upstream signal is prohibited, the contact point P1 and the contact point P3 constituting the switching circuit 83 are connected, and the contact point P4 and the contact point P6 are connected. 87 and the input terminal T1
And the output terminal T2 is grounded via the amplifier circuit 85 and the resistor 89. Then, by mistake, the input terminal T1
Input signal from the output terminal T2
Will not be output. The resistance value of the resistor 87 is
The impedance is selected so that the impedance before and after the input terminal T1 matches. That is, the impedance is selected so that the impedance of the transmission line connected to the input terminal T1 matches the impedance when the inside of the upstream signal amplifier 10 is viewed from the input terminal T1. Similarly, the resistance value of the resistor 89 is
The impedance is selected so that the impedance of the transmission line connected to the output terminal T2 matches the impedance when the inside of the upstream signal amplifier 10 is viewed from the output terminal T2.

[0007]

However, even when the contact points P1 and P3 are connected and the contact points P4 and P6 are connected, the gap between the contact points P1 and P2, and the contact point between the contact points P4 and P5 can be reduced. The gap and the gap between the contact points P3 and P6 are not completely insulated but act like a capacitor. Therefore, high-frequency noise may be transmitted from the input terminal T1 to the output terminal T2 by jumping over each gap. In addition, the noise transmitted in this manner is greatly attenuated when jumping over each gap, but conversely is greatly amplified when passing through the amplifier circuits 81 and 85, and in some cases, the input terminal T1 May be amplified and output from the output terminal T2. Therefore, a technique for reliably attenuating such noise is demanded. In this case, it is necessary to consider not only the improvement of the noise attenuation rate but also the impedance matching at the input terminal and the output terminal.

Therefore, the present invention improves the attenuation rate of noise transmitted in a state where transmission of an upstream signal is prohibited,
It is another object of the present invention to match impedances before and after an input terminal and an output terminal of a transmission signal amplifier (upstream signal amplifier).

[0009]

Means for Solving the Problems and Effects of the Invention In order to achieve such an object, a transmission signal amplifier according to the first invention is provided via a CATV transmission line. In a bidirectional CATV system configured to be able to transmit an uplink signal from a terminal terminal side to a center device, an upstream signal provided on the CATV transmission line and transmitted at least from the terminal terminal side to the center device is amplified. An input terminal and an output terminal for connecting the CATV transmission line, and a transmission signal amplifier provided in a device transmission path from the input terminal to the output terminal,
An amplifier circuit that amplifies a signal input from the input terminal side and outputs the amplified signal to the output terminal side, an interrupted circuit that disconnects the transmission path in the device based on a command from the outside, A signal transmission prohibition command circuit for issuing a transmission path disconnection command for disconnecting a transmission path in the device, a power supply cutoff circuit for interrupting supply of operating power to the amplifier circuit based on an external command, and the input terminal An input-side termination circuit configured to have the same impedance as the impedance of the transmission line connected to the input-side ground switching circuit that grounds the input terminal via the input-side termination circuit based on an external command; An output-side termination circuit configured to have the same impedance as the impedance of the transmission line connected to the output terminal, and the output through the output-side termination circuit based on an external command. An output-side ground switching circuit for grounding a child, the signal transmission prohibition command circuit, when issuing a transmission path disconnection command to the intermittent circuit, for the power supply cutoff circuit, to the amplification circuit Issue a power supply cutoff command to cut off the supply of the operating power of the input terminal, and further, to the input side ground switching circuit, an input terminal grounding command for grounding the input terminal via the input side termination circuit. And outputting an output terminal grounding command to the output side ground switching circuit to ground the output terminal via the output side termination circuit.

According to the transmission signal amplifier of the present invention,
If the transmission path disconnection command, the power supply cutoff command, the input terminal grounding command, and the output terminal grounding command are not issued from the signal transmission prohibition command circuit, that is, if the transmission of the upstream signal is permitted, the transmission signal amplifier The upstream signal transmitted via the transmission line from the various devices provided in the preceding stage is input from the input terminal into the transmission signal amplifier, and is provided on the transmission path in the device from the input terminal to the output terminal. The amplified signal is output from the output terminal to the outside of the transmission signal amplifier, and is transmitted via a transmission line to various devices provided at the subsequent stage of the transmission signal amplifier.

On the other hand, when prohibiting the transmission of the upstream signal, the signal transmission prohibition command circuit issues a transmission path disconnection command to the intermittent circuit, so that the internal transmission path from the input terminal to the output terminal is transmitted. Cut. If the internal transmission path from the input terminal to the output terminal is cut in this way, the signal and noise input from the input terminal should not reach the output terminal. However, as described above, in reality, noise having a high frequency may jump over a cut portion, and this noise is amplified by an amplifier circuit and output from an output terminal.

Therefore, in the transmission signal amplifier according to the present invention, the signal transmission prohibition command circuit issues a transmission path disconnection command to the intermittent circuit to disconnect the transmission path in the device, and the power transmission cutoff circuit transmits the transmission path disconnection command to the intermittent circuit. By issuing a power supply cut-off command, the supply of operating power to the amplifier circuit is cut off. When the supply of the operating power to the amplifier circuit is cut off in this way, the amplifier circuit usually turns over from the amplification function and performs the attenuation function. Even if there is noise, it is greatly attenuated by the amplifier circuit and output from the output terminal.

As described above, according to the transmission signal amplifier of the present invention, almost no noise is output from the output terminal, and even if it is output, the output noise is greatly reduced. Since it is attenuated, various devices connected to the end of the output terminal via the CATV transmission line rarely malfunction due to the influence of noise.

In addition, in the transmission signal amplifier according to the present invention, the signal transmission prohibition command circuit issues a transmission path disconnection command to the intermittent circuit and a power supply cutoff command to the power supply cutoff circuit. Further, it issues an input terminal ground command to the input-side ground switching circuit and issues an output terminal ground command to the output-side ground switching circuit. Then, the input side ground switching circuit grounds the input terminal via the input side termination circuit according to the input terminal grounding command, and the output side ground switching circuit grounds the output terminal via the output side termination circuit according to the output terminal grounding command. I do. The input-side termination circuit is configured to have the same impedance as the impedance of the transmission line connected to the input terminal, and the output-side termination circuit is configured to have the same impedance as the transmission line connected to the output terminal. When the input terminal is grounded via the input-side termination circuit and the input terminal is grounded via the output-side termination circuit, the impedances before and after the input terminal and the output terminal match. Therefore, when the input terminal ground command and the output terminal ground command are issued from the signal transmission prohibition command circuit, even if a signal or noise is input from the input terminal or output terminal, this signal or noise should be reflected. Without being led to the ground.

As described above, according to the transmission signal amplifier according to the present invention, the impedances before and after the input terminal and the output terminal can be matched, so that the connection between the input terminal and the output terminal via the CATV transmission line can be made. Various devices can be operated satisfactorily.

The signal transmission prohibition command circuit may be configured to output a transmission path disconnection command, a power supply cutoff command, an input terminal ground command, and an output terminal ground command in response to a command from the center device. , It may be configured to determine the use status of the CATV transmission line and issue a command, or to allocate in advance a time zone in which the transmission line can be used for each terminal device and determine whether the time zone is available. It may be configured to determine whether or not to issue a command. The signal transmission prohibition command circuit may be provided with input means such as a push button, and may be configured to issue a command in accordance with the operation mode of the input means by the administrator of the CATV system or the like.

Further, the bidirectional CATV system according to the second aspect of the present invention can transmit an upstream signal from a terminal terminal side to a center device via a CATV transmission line. A transmission signal amplifier according to claim 1 provided on said CATV transmission line, and amplifying an upstream signal transmitted from said terminal terminal side to said center device by said transmission signal amplifier. It is characterized by.

In the bidirectional CATV system according to the present invention, since the transmission signal amplifier according to the first invention is provided on the CATV transmission line, the effect of the transmission signal amplifier according to the first invention can be obtained. That is, even if noise is input to the transmission signal amplifier, the noise is hardly output from the transmission signal amplifier, and even if it is output, the output noise is greatly attenuated. Even if the noise corresponding to the plurality of branch lines, distribution lines, and drop-in lines is superimposed, the noise is slight, and the effect that the center device or the like rarely malfunctions due to the noise is obtained.

Further, since the impedances before and after the transmission signal amplifier can be matched, various transmission devices provided on the CATV transmission line, terminal devices connected to the terminal terminals, center devices, etc. can be satisfactorily operated. Can also be obtained.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. First, the configuration of the bidirectional CATV system of the present embodiment will be described. Figure 1 shows a bidirectional CAT
It is a block diagram for explaining the configuration of the V system,
FIG. 2 is a block diagram for explaining the configuration of the upstream signal amplifier.

As shown in FIG. 1, the bidirectional CATV system of this embodiment has a head end 1 and a main branch amplifier 2.
, Branch amplifier 3, tap-off 4, bidirectional amplifier 5
, A distributor 6, and a terminal terminal 7. One terminal 7 is connected to a television receiver 8 for receiving, demodulating and reproducing a downstream signal, and another terminal 7 is connected to a personal computer 9 with a built-in cable modem.
(Hereinafter simply referred to as “personal computer 9”), and transmitting various data (up signals) from the personal computer 9 to the headend 1 to make a reservation for viewing a pay program, perform television shopping, and the like. It is configured to be able to.

The bidirectional amplifier 5 includes a downstream signal amplifier 5a for amplifying a downstream signal transmitted from the head end 1 to the terminal terminal 7, and the terminal terminal 7 which is a characteristic part of the bidirectional CATV system of the present embodiment. Signal amplifier 5b for amplifying the upstream signal transmitted from the head end 1 to the head end 1
And is constituted by. The bidirectional C of this embodiment is used.
The amplifiers such as the main branch amplifier 2 and the branch amplifier 3 constituting the ATV system also include the same upstream signal amplifier as the bidirectional amplifier 5, but hereinafter, the upstream signal amplifier 5b provided in the bidirectional amplifier 5 will be described. And only the description of the upstream signal amplifier provided in the main branch amplifier 2 and the branch amplifier 3 will be omitted.

As shown in FIG. 2A, the upstream signal amplifier 5b has an input terminal T1 for connecting to the terminal terminal 7 side,
An output terminal T2 for connection to the headend 1 side and a transmission path in the device from the input terminal T1 to the output terminal T2 are provided to amplify a signal input from the input terminal T1 and output it to the output terminal T2. Amplifying circuits 11 and 13, and power supply cutoff circuits 15 and 17 which are provided on a power supply line connecting the power supply and the amplifying circuits 11 and 13 and switch between supply and cutoff of operating power to the amplifier circuits 11 and 13. A control circuit 19 for issuing a command to each section in the upstream signal amplifier 5b, an intermittent circuit 21 for cutting off a transmission path in the device based on a command from the control circuit 19, and a CATV connected to the input terminal T1.
Resistance 23 having the same impedance as the transmission line impedance
An input-side ground switching circuit 25 that grounds the input terminal T1 via the resistor 23 based on a command from the control circuit 19;
A resistor 27 having the same impedance as that of the CATV transmission line connected to the output terminal T2, and an output-side ground switching circuit 29 for grounding the output terminal T2 via the resistor 27 based on a command from the control circuit 19 are provided. .

The control circuit 19 switches the transmission / reception of the transmission of the upstream signal in response to a command from the head end 1. When the transmission of the upstream signal is prohibited, the control circuit 19 And issues a transmission path disconnection command, issues a power supply cutoff command to the power supply cutoff circuits 15 and 17, issues an input terminal grounding command to the input side grounding switching circuit 25, and issues an input terminal grounding command to the output side grounding switching circuit 29. It is configured to issue an output terminal ground command.

When the transmission path disconnection command is not issued from the control circuit 19, the intermittent circuit 21 keeps the connection state. Similarly, when the power supply cutoff command is not issued from the control circuit 19, the power supply cutoff circuit 15,
Reference numeral 17 denotes a state in which operating power is supplied from the power supply circuit to the amplifier circuits 11 and 13. Similarly, when the input terminal ground command and the output terminal ground command are not issued from the control circuit 19, the input-side ground switching circuit 25 holds the input terminal T1 and the resistor 23 in a non-conductive state, and The side ground switching circuit 29 holds the output terminal T2 and the resistor 27 in a non-conductive state.

On the other hand, when a transmission path disconnection command, a power supply cutoff command, an input terminal grounding command, and an output terminal grounding command are issued from the control circuit 19, the intermittent circuit 21 cuts off the transmission path in the device and the power supply cutoff circuit 15 , 17 are amplifier circuits 11,
The input-side ground switching circuit 25 grounds the input terminal T1 via the resistor 23, and the output-side ground switching circuit 29 grounds the output terminal T2 via the resistor 27.

If, for example, the power plug of the upstream signal amplifier 5b is disconnected from the outlet and power supply to the entire upstream signal amplifier 5b is stopped, the intermittent circuit 2
1 is in a disconnected state, the power supply cutoff circuits 15 and 17 cut off the supply of operating power to the amplifier circuits 11 and 13, the input side ground switching circuit 25 grounds the input terminal T1 via the resistor 23, and the output side. The ground switching circuit 29 grounds the output terminal T2 via the resistor 27, that is, the same as when the control circuit 19 issues a transmission path disconnection command, a power supply cutoff command, an input terminal grounding command, and an output terminal grounding command. It is configured to be in a state.

Next, a specific circuit configuration of the input-side ground switching circuit 25 will be described. The input side ground switching circuit 25
As shown in FIG. 2B, a terminal T3 for connecting to the control circuit 19 and a terminal T4 for connecting to the input terminal T1.
A terminal T5 for connecting to the amplifier circuit 11;
3, a terminal T6 for connection to the terminal 3, a choke coil 31 for blocking an upstream signal, and capacitors 33 and 35 for passing an upstream signal.
And a diode 37. Therefore, the terminal T3
Is zero, the diode 37 is in the OFF state, so that the upstream signal input from the terminal T4 is output from the terminal T5 via the upstream signal passing capacitors 33 and 35. Is set to the HIGH level, the diode 37 is turned on. Therefore, the terminal T4 is connected to the up-signal passing capacitor 33, the diode 3
7, the terminal T6 and the resistor 23 are grounded. That is, the input terminal T1 is grounded via the resistor 23 for a signal having a high frequency. Then, when the control circuit 19 sets the potential of the terminal T3 to the HIGH level, the input terminal grounding command to the input-side ground switching circuit 25 is issued.

Since the output-side ground switching circuit 29 has exactly the same configuration as the input-side ground switching circuit 25, the description of the output-side ground switching circuit 29 is omitted. In this embodiment, the bidirectional amplifier 5 (upstream signal amplifier 5b) corresponds to the above-described transmission signal amplifier, the control circuit 19 corresponds to the above-described signal transmission prohibition command circuit, and the resistor 23 corresponds to the above-described input-side termination. The resistor 27 corresponds to the output-side termination circuit described above.

Next, the effect of the bidirectional CATV system (upstream signal amplifier 5b) of this embodiment will be described. According to the upstream signal amplifier 5b of the present embodiment, when the transmission of the upstream signal is prohibited, the control circuit 19 issues a transmission path disconnection command to the intermittent circuit 21 to transmit the internal transmission path from the input terminal T1 to the output terminal T2. And a power supply cutoff command is issued to the power supply cutoff circuits 15 and 17 to amplify the amplifier circuit 1.
Since the supply of the operating power to the switching circuits 1 and 13 is cut off, even if there is noise that jumps over the location cut by the intermittent circuit 21, the noise is greatly attenuated by the amplifier circuits 11 and 13 and output from the output terminal. Become. Therefore, noise is hardly output from the output terminal T2, and even if it is output, the output noise is greatly attenuated. It hardly affects the operation of the head end 1 or the like connected earlier.

In addition, when prohibiting the transmission of the upstream signal,
The control circuit 19 also issues an input terminal grounding command and an output terminal grounding command to the input-side ground switching circuit 25 and the output-side ground switching circuit 29, respectively, so that the CATV connected to the input terminal T1.
Resistance 23 having the same impedance as the transmission line impedance
, The input terminal T1 is grounded, and the output terminal T
Since the output terminal T2 is grounded via the resistor 27 having the same impedance as the impedance of the CATV transmission line connected to the terminal 2, the impedances before and after the input terminal T1 and the output terminal T2 match. Therefore, when an input terminal ground command and an output terminal ground command are issued from the control circuit 19, even if a signal or noise is input from the input terminal T1 or the output terminal T2, the signal or noise is reflected. Instead, it is connected to the personal computer 9 connected to the terminal terminal of the bidirectional amplifier 5 (upstream signal amplifier 5b) or to the headend side of the bidirectional amplifier 5 (upstream signal amplifier 5b). The center device and the like can be operated well.

The embodiment of the present invention has been described above. However, the present invention is not limited to the above-described embodiment, and it is needless to say that the present invention may be implemented in various modes. For example, in the embodiment, the input terminal circuit,
A resistor is adopted as the output side termination circuit, and the input terminal T1 and the output terminal T
It is configured to switch the connection between 2 and the resistor,
Other circuit elements may be employed as long as they can be controlled by the control circuit 19. Specifically, instead of being grounded via a diode and a resistor, it may be configured to be grounded via a PIN diode, or the input side ground switching circuit 2
5. The output-side ground switching circuit 29 may be configured by a relay.

In the embodiment, the control circuit 19 receives an instruction from the head end 1 and permits / controls transmission of an uplink signal.
Switch prohibition (intermittent circuit 21, power supply cutoff circuit 1)
5, 17, the input-side ground switching circuit 25, and the output-side ground switching circuit 29). However, the control circuit 19 is provided with input means such as push buttons, so that the CATV system administrator The transmission of the upstream signal may be switched between permission and prohibition in accordance with the operation mode of the input means such as the above.

In the embodiment, various data transmitted from the personal computer 9 to the head end 1 have been described as an example of an upstream signal. In addition, video data from a television camera during shooting is also transmitted. The signal is transmitted from the terminal terminal 7 to the head end 1 as a signal, and the head end 1 receives the data, processes the data (converts the down signal into a frequency, etc.), and converts the data into the terminal terminal 7 (the television receiver 8 connected thereto). ) Is also possible. In such a configuration, the video taken by the television camera can be broadcast live to the CATV system subscriber.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a bidirectional CATV system according to an embodiment.

FIGS. 2A and 2B are a block diagram for explaining a circuit configuration of an uplink signal amplifier and a block diagram for explaining a circuit configuration of an input-side ground switching circuit; FIGS.

FIG. 3 is a block diagram for explaining a circuit configuration of a conventional uplink signal amplifier.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Head end 2 ... Trunk branch amplifier 3 ... Branch amplifier 4 ... Tap-off 5 ... Bidirectional amplifier 5
a: Down signal amplifier 5b: Up signal amplifier 6 ...
Distributor 7 ... Terminal terminal 8 ... TV receiver 9 ...
Personal computer with built-in cable modem 10 ...
Conventional upstream signal amplifier 11, 13 ... amplifier circuit 1
5, 17: power supply cutoff circuit 19: control circuit 2
DESCRIPTION OF SYMBOLS 1 ... Intermittent circuit 23, 27 ... Resistance 25 ... Input side grounding switching circuit 29 ... Output side grounding switching circuit 31 ... Choke coil 33, 35 ... Upstream signal passing capacitor 37 ... Diode 81 ... Amplification circuit 83 ... Switching Circuit 85 ... Amplifier circuit 87 ... Resistor 89 ... Resistor 91
... Control circuits P1, P2, P3, P4, P5, P6 ...
Contact T1 ... Input terminal T2 ... Output terminal T3, T
4, T5, T6 ... terminals.

Claims (2)

[Claims] 1. A bidirectional CATV system configured to be able to transmit an uplink signal from a terminal terminal side to a center device via a CATV transmission line, wherein the bidirectional CATV system is provided on the CATV transmission line, and is provided at least from the terminal terminal side. A transmission signal amplifier for amplifying an upstream signal transmitted to a center device, comprising: an input terminal and an output terminal for connecting the CATV transmission line; and a transmission path in the device from the input terminal to the output terminal. An amplifier circuit for amplifying a signal input from the input terminal side and outputting the amplified signal to the output terminal side; an intermittent circuit for disconnecting the transmission path in the device based on an external command; A signal transmission prohibition command circuit for issuing a transmission path disconnection command for disconnecting the transmission path in the device; and an operating power supply to the amplification circuit based on an external command. A power supply cutoff circuit for cutting off the supply of power, an input-side termination circuit configured to have the same impedance as the impedance of the transmission line connected to the input terminal, and the input-side termination circuit based on an external command. An input-side ground switching circuit that grounds the input terminal; an output-side termination circuit configured to have the same impedance as a transmission line connected to the output terminal; and the output-side termination circuit based on an external command. An output-side ground switching circuit that grounds the output terminal through the signal transmission prohibition command circuit, when issuing a transmission path disconnection command to the intermittent circuit, for the power supply cutoff circuit, Issue a power supply cutoff command to cut off the supply of operating power to the amplifier circuit,
Further, an input terminal grounding command for grounding the input terminal through the input side termination circuit is issued to the input side ground switching circuit, and the output side termination circuit is output to the output side ground switching circuit. A transmission signal amplifier for issuing an output terminal ground command for grounding the output terminal via a circuit. 2. A bidirectional CATV system configured to transmit an uplink signal from a terminal terminal side to a center device via a CATV transmission line, wherein the transmission signal according to claim 1 is provided on the CATV transmission line. A bidirectional CATV system, comprising an amplifier, and amplifying an upstream signal transmitted from the terminal terminal side to the center device by the transmission signal amplifier.