JP2001275099A - Tap-off and catv system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that the level of noise reaching a center increases when the noise input is hardly made from a subscriber terminal, etc., connected to a tap-off with small loss installed at a distance from a repeating amplifier although a CATV system transmission line has large loss to an incoming signal and the noise from the subscriber terminal is hardly inputted since the branch loss and insertion loss of the tap-off are so designed that the level of an outgoing signal is equal at each subscriber terminal and then the branch loss is set large for a tap-off close to the repeating amplifier. SOLUTION: At a tap-off arranged at a specific position on a tap-off line, an attenuator is arranged in an incoming transmission line arranged between two directional filters and incoming mixed noise is reduced without affecting the outgoing signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tap-off system and a CATV system installed on a CATV transmission line, and more particularly to a tap-off system and a CATV system for reducing a signal noise from a subscriber terminal remote from a relay amplifier.

[0002]

2. Description of the Related Art In a current CATV system, as shown in FIG. 4, a CATV transmission line extends from a center device 1, and relay amplifiers 2 and 3 are installed at predetermined intervals on this transmission line. Has multiple tap-offs 4, 5, 6,
7 and 8 are connected in cascade, and the subscriber terminal 9 is connected to each tap-off.

[0003] The tap-off to which the subscriber terminal connects is
It has an input / output terminal, a branch circuit, and a distribution circuit as a basic configuration. The signal sent from the center is branched by the branch circuit, input to the distribution circuit, and distributed from the distribution circuit to each subscriber terminal. On the other hand, the upstream signal transmitted from the subscriber terminal is input to the branch circuit from the distribution circuit, and is combined with the signal from the terminal at the subsequent stage in the branch circuit and transmitted to the center.

In the above CATV system, ingress noise from a subscriber terminal or a vacant terminal of a distribution circuit is CATV.
It may be mixed into the transmission path and cause various problems. For this reason, various configurations for preventing ingress noise at tap-off have been proposed. For example, JP-A-04-2
Japanese Patent No. 40942 proposes a tap-off configuration in order to solve the problem that many terminals do not respond to polling from the center due to ingress noise. Here, a distributor and a switch are installed on the upstream transmission line within the tap-off, the upstream signal from the terminal is distributed by the distributor, and a carrier signal is extracted from the distributed signal by a bandpass filter,
This signal controls to close the normally open switch. With this configuration, it is possible to prevent ingress noise from, for example, a vacant terminal of tap-off.

[0005]

On the other hand, in a tap-off line of a CATV transmission line, cable loss and tap-off branch loss and insertion loss are designed so that the level of a downstream signal at each subscriber terminal is equalized. . For this reason, since tap loss close to the relay amplifier has a large branch loss, loss is large even for uplink signals, and ingress noise from subscriber terminals and the like is small. However, as for the tap-off provided at a place remote from the relay amplifier, a tap-off having a small branch loss is selected because a loss of a downlink signal increases due to a cable loss. For this reason, if ingress noise is mixed in from a subscriber terminal or the like connected to such a tap having a small loss, the level of noise reaching the center increases.

An object of the present invention is to solve such a problem and reduce upstream inflow noise from a subscriber terminal or the like without affecting downstream signals.

[0007]

According to the present invention, there is provided a tap-off device comprising: an input terminal; an output terminal; a branch circuit for branching a part of a signal propagating between these terminals;
A distribution circuit for distributing the branched signal to the subscriber terminal, wherein two directional filters are arranged in the signal path;
The two directional filters are respectively connected by a downstream signal transmission line and an upstream signal transmission line, and an attenuator is installed on the upstream signal transmission line. The two directional filters can be arranged between the branch circuit and the distribution circuit, or between the input terminal and the branch circuit, or between the branch circuit and the output terminal. The attenuator may be a variable attenuator.

Further, the CATV system of the present invention comprises a center device, a CATV transmission line, a relay amplifier installed on the CATV transmission line, a plurality of tap-offs cascaded to the relay amplifier, and subscriber terminals connected to the tap-offs. The upstream signal level is attenuated within at least one tap-off. The tap-off in which the uplink signal level is adjusted to attenuate takes the above-described tap-off configuration.

Further, in the CATV system of the present invention, among the plurality of tap-offs cascaded to the relay amplifier, one or more tap-offs arranged in order from the tap-off farthest from the relay amplifier are connected between the branch circuit and the distribution circuit. , Two directional filters are arranged, and the two directional filters are connected by a downlink signal transmission path and an uplink signal transmission path, respectively, and are a tap-off in which an attenuator is installed in the uplink signal transmission path. In another CATV system according to the present invention, among a plurality of tap-offs cascaded to a relay amplifier, one tap-off disposed near a central portion is provided between an input terminal and a branch circuit or between a branch circuit and an output terminal. 2
Two directional filters are arranged, and the two directional filters are connected by a downlink signal transmission path and an uplink signal transmission path, respectively.
This is a tap-off where an attenuator is installed on the upstream signal transmission path.

According to the present invention, CATV according to the present invention
In the system, the loss balance of the upstream signal can be made uniform, and the upstream ingress noise can be reduced without affecting the downstream signal.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of a tap-off configuration according to the present invention. In FIG. 1, an input terminal 10 and an output terminal 11 are formed at a tap-off, and a branch circuit 14 is arranged between these terminals. A downstream signal from the center to the subscriber terminal is branched by the branch circuit 14, and one of the signals is output from the output terminal 1
The signal is sent from 1 to the subsequent tap-off, and the other signal is sent to the distribution circuit 16 in the tap-off. Two directional filters 12, 13 are provided between the branch circuit 14 and the distribution circuit 16, and these directional filters 12, 13
1 via an upstream transmission line 22. A variable attenuator 15 is arranged on the upstream transmission line 22 so that the level of the upstream signal can be adjusted. Branch output terminals 17, 18, 19, 20 are formed in the distribution circuit, and these terminals are connected to subscriber terminals.

The downstream signal branched by the branch circuit 14 is transmitted through the directional filter 12 to the downstream transmission line 21 within the tap-off.
From the distribution circuit 16 to the subscriber terminal. On the other hand, the upstream signal from the subscriber terminal passes from the distribution circuit 16 through the upstream transmission line 22 within the tap-off, is multiplexed with the upstream signal from the subsequent tap-off in the branch circuit 14, and is sent to the center device.

At this time, at tap-off with a small loss, the ingress noise returns to the center device together with the upstream signal without much loss. For this reason, the variable attenuator 15 is provided on the upstream transmission line 22 to appropriately attenuate the levels of the upstream signal and the ingress noise. The amount of attenuation can be calculated in advance to provide an attenuator having a predetermined amount of attenuation (the same applies to the following configurations). As a result, it is possible to arbitrarily set the arrival level of the upstream signal to the center without affecting the downstream signal.

FIG. 2 shows another example of the tap-off according to the present invention. Here, in contrast to the configuration of FIG. 1, two directional filters 12, 1 connected by a downlink transmission line 21 and an uplink transmission line 22,
3 is provided between the input terminal 10 and the branch circuit 14. The variable attenuator 15 is provided on the upstream transmission line 22. In the configuration of FIG. 1, the upstream signal whose level is attenuated by the variable attenuator 15 is only the upstream signal from the subscriber terminal connected to the tap-off and the ingress noise from the tap-off. However, in the configuration of FIG. 2, in addition to the upstream signal from the subscriber terminal connected to the tap-off, the upstream signal and the ingress noise from the subsequent subscriber terminal connected to the tap-off are attenuated by the variable attenuator 15.

FIG. 3 shows another example of tap-off. In the configuration of FIG. 3, two directional filters 12 and 13 connected by a downstream transmission line 21 and an upstream transmission line 22 are provided between the branch circuit 14 and the output terminal 11. The variable attenuator 15 is also installed on the upstream transmission line 22. In the configuration of FIG. 3, the variable attenuator 15 attenuates an upstream signal and an ingress noise transmitted from a subscriber terminal connected to a tap-off stage subsequent to the tap-off.

A configuration in which the above-described tap-off is arranged on a CATV transmission line (tap off-line) will be described. FIG.
In the tap-off configuration, only the upstream signal and the ingress noise from the subscriber terminal connected to the tap-off are attenuated.
For this reason, the tap-off in FIG. 1 is applied to a predetermined number of tap-offs sequentially from the last stage of the tap-off line. The number of tap-offs having this configuration is appropriately changed according to the design conditions of the entire system.

In the tap-off of FIG. 2, the variable attenuator 15 reduces the level of the upstream signal and the ingress noise from all the subscriber terminals connected to the tap-off and the subsequent tap-off. Therefore, for example, the present invention can be applied to only one tap-off at a substantially central portion among a plurality of tap-offs arranged in cascade in a tap-off line. However, not limited to this mode, in consideration of the level of the entire uplink signal,
Several locations can be installed during tap-offline.

In the tap-off configuration of FIG. 3, since the level of the upstream signal passing through the subsequent-stage tap-off is reduced, it cannot be installed at the last stage. Install inside.

It is also possible to install both the tap-off of the configuration of FIG. 1 and the tap-off of the configuration of FIG. 2 or 3 as tap-off lines as long as the conditions of the system are satisfied.

By installing an attenuator on the upstream transmission line during tap-off, the upstream signal from the subscriber terminal is also attenuated. Is automatically adjusted, and the required carrier passes through the transmission path at an appropriate level, so that no particular problem occurs.

[0022]

According to the tap-off and CATV system of the present invention, an attenuator is installed on an upstream transmission line within a predetermined tap-off during tap-off and the upstream level is controlled to reduce upstream ingress noise. it can.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration example of tap-off according to the present invention.

FIG. 2 is a block diagram showing another configuration example of the tap-off of the present invention.

FIG. 3 is a block diagram showing another configuration example of the tap-off of the present invention.

FIG. 4 is a configuration diagram of a CATV system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Center device 2, 3 Relay amplifier 4, 5, 6, 7, 8 Tap-off 9 Subscriber terminal 10 Input terminal 11 Output terminal 12, 13 Directional filter 14 Branch circuit 15 Variable attenuator 16 Distribution circuit 17, 18, 19, Reference Signs List 20 branch output terminal 21 downlink transmission line 22 uplink transmission line

Claims (10)

[Claims] 1. A tap-off system comprising an input terminal and an output terminal, a branch circuit for branching a signal propagating between these terminals, and a distribution circuit for distributing the branched signal to subscriber terminals. A tap-off wherein a directional filter is provided, the two directional filters are connected by a downlink signal transmission path and an uplink signal transmission path, respectively, and an attenuator is installed in the uplink signal transmission path. 2. The tap-off according to claim 1, wherein two directional filters are arranged between the branch circuit and the distribution circuit. 3. The tap-off according to claim 1, wherein two directional filters are arranged between the input terminal and the branch circuit. 4. The tap-off according to claim 1, wherein two directional filters are arranged between the branch circuit and an output terminal. 5. The tap-off according to claim 1, wherein the attenuator is a variable attenuator. 6. A center device, a CATV transmission line, and the CA
In a CATV system including a relay amplifier installed on a TV transmission line and a plurality of tap-offs cascaded to the relay amplifier and subscriber terminals connected to the tap-off, an upstream signal level is attenuated within at least one tap-off. CATV system characterized by the above-mentioned. 7. The tap-off in which the upstream signal level is attenuated and adjusted includes an input terminal and an output terminal, a branch circuit for branching a signal propagating between these terminals, and a distribution of the branched signal to subscriber terminals. A tap-off provided with a distribution circuit, wherein two directional filters are arranged in a signal path, and the two directional filters are respectively connected by a downlink signal transmission path and an uplink signal transmission path, and are connected to an uplink signal transmission path. 7. The CATV system according to claim 6, wherein an attenuator is provided. 8. In a plurality of tap-offs cascaded to a relay amplifier, one or more tap-offs arranged in order from a tap-off farthest from the relay amplifier branch an input terminal and an output terminal and a signal propagating between these terminals. And a distribution circuit for distributing the branched signal to the subscriber terminal.
Two directional filters are arranged, and the two directional filters are connected by a downlink signal transmission path and an uplink signal transmission path, respectively.
7. The CATV system according to claim 6, wherein tap-off is performed in which an attenuator is installed in an upstream signal transmission path. 9. In a plurality of tap-offs cascaded to a relay amplifier, one or a plurality of tap-offs include an input terminal and an output terminal, a branch circuit for branching a signal propagating between these terminals, and adding a branched signal. A distribution circuit for distributing the signal to the user terminal, wherein two directional filters are arranged between the input terminal and the branch circuit or between the branch circuit and the output terminal, and the two directional filters are connected to a downstream signal transmission line. 7. A tap-off connection in which an attenuator is installed in the upstream signal transmission line, and the attenuator is connected to the upstream signal transmission line.
The CATV system as described. 10. The CATV system according to claim 9, wherein one tap-off is arranged near a center of a plurality of tap-offs connected in cascade.