JPS61199336A - Protecting device for communication - Google Patents

Abstract

PURPOSE:To block an unnecessary high frequency signal component by providing the 1st selector blocking a signal of an incoming frequency band and terminating the input of the 1st selector via the 2nd selector passing a signal of a frequency band blocked by the 1st selector. CONSTITUTION:A high pass filter (HPF) 117 passes an outgoing signal and blocks an incoming signal by deciding constants 109 116 and a low pass filter (LPF) 129 passes an incoming signal and blocks an outgoing signal by selecting constants 121 128. The outgoing signal inputted to an input terminal 101 passes through a fuse 106 and a capacitor 108 and is processed selectively by the HPF 117 and led to an output terminal 102. Since the LPD 129 is set so that the incoming signal frequency band only is passed, on outgoing signal flows to the LPF 129. When an unnecessary high frequency signal component at the incoming signal frequency band generated from a subscriber's equipment is fed to the output terminal 102, the invasion of the signal toward the input terminal 101 is blocked by the HPF 117.

Description

[Detailed Description of the Invention] Industrial Application Field This invention is a communication system that communicates down signals from a center to a subscriber's home and up signals from a subscriber's home to a center via a single coaxial cable. The present invention relates to a communication safety device suitable for a two-way CATV system.

Conventional technology When a coaxial cable is drawn from a branch or distributor in a two-way CATV system to a subscriber's home, surge voltages caused by lightning strikes may enter the subscriber's home from the system, and abnormal voltages due to earth leakage may enter the subscriber's home from the system. A protector is interposed between the branch/distributor and the subscriber's house to prevent the system from entering the subscriber's house or from the subscriber's house. This protector is usually installed at the coaxial cable entrance at the subscriber's premises. FIG. 2 is a circuit diagram showing an example of a conventional protector. Components that are the same as those in FIG. 1 are given the same numbers. The protector has input terminal 101
and an output terminal +02 are provided, the coaxial cable drawn from the branch or distributor of the bidirectional CATV system is connected to the input terminal +01, and the coaxial cable drawn into the subscriber's home is connected to the output terminal 102. . One terminal of a lightning arrester 105 is connected to the internal conductor side terminal +03 of the input terminal 101, and the other terminal is connected to A-. In addition, the internal conductor side terminals 10 and 3 and the lightning arrester +0
One terminal of a fuse 106 is connected to the connection point 5, and the other terminal is connected to one terminal of a choke coil 107 and a capacitor 108.
The other terminal of 07 is connected to ground. The external conductor side terminal +04 of the input terminal 101 is connected to ground. The other terminal of the capacitor 108 is connected to the internal conductor side terminal 118 of the output terminal 102. The external conductor side terminal 119 is connected to ground via a capacitor 120.

When a surge voltage due to a reservoir etc. is applied to the internal conductor side terminal 103 of the input terminal 101 via the internal conductor of the coaxial cable drawn from the bidirectional CATV system,
The surge voltage is immediately discharged to the ground by the lightning arrester 105 and no surge voltage is transmitted to the output terminal 102. In addition, when a surge voltage is transmitted through the outer conductor of the coaxial cable and applied to the outer conductor side terminal 104, the outer conductor side terminal 104 is grounded, and the inner conductor side terminal 103 of the rectangular terminal +01 is connected to the fuse 10.
6 and is connected to the ground by the choke coil 107, and has sufficiently low impedance with respect to the ground in terms of direct current.
It is connected to the output terminal +02 via a capacitor 108, and has a sufficiently high impedance in terms of direct current with respect to the internal conductor side terminal 118 of the output terminal +02.

Further, the external conductor side terminal 119 of the output terminal 102 is connected to the ground via a capacitor 120, and has a sufficiently high impedance with respect to the ground in terms of direct current. Therefore, even if an abnormal voltage due to leakage is applied to the input terminal 1011\ from the bidirectional CATV system through the coaxial cable, the abnormal voltage will not be generated at the output terminal +02. The external conductor terminal 119 of the output terminal 102 is connected to the ground via the capacitor 120 because the external conductor terminal 104 of the input terminal 101 may have an abnormal voltage with respect to the earth ground, and in this case, the abnormal voltage is This is to prevent this from being transmitted to the subscriber's home since it will also be transmitted from the ground system. The fuse 106 is provided to protect the bidirectional CATV system and the protector itself when the leakage current is large.

Problems to be Solved by the Invention In recent years, two-way CATV has been in the spotlight even in Japan, and facilities are being installed. However, at the current stage of two-way CATV, it is rare for all subscribers to sign a contract for two-way communication at the same time as the installation of the facility; It is expected that there will be more. This is the same situation in the United States, where two-way CATV is more popular than in Japan. However, even if such a situation is expected, in order to respond to subscribers' requests for two-way communication at any time, two-way CATV facilities are designed from the beginning of installation to have a system that extends from the center to the safety device at the end of the facility's controlled area. The upstream signal system must be made bidirectional so that subscribers can use the uplink signal system at any time.

One of the major problems with bidirectional CATV systems is heating noise in the uplink S system. Bidirectional C as mentioned above
Since the ATV facility was first installed, the entire area of the facility has been interactive. Regardless of whether the subscriber uses the uplink signal system or not, terminals capable of transmitting uplink signals are being installed in all subscriber homes. Therefore, unnecessary heating noise in the high frequency range flows in from all subscriber homes, increasing the noise power in the upstream signal system, which is a very harmful and difficult problem to solve.

Basically, heating noise is random noise such as thermal noise and shot noise generated by the appliances used, but depending on the conditions, it may also be used (A) Random noise at the subscriber's home after the safety device. Unnecessary high-frequency signal components generated by home television reception boosters and television receivers.

(B) Intrusion of external radio waves due to the use of poor-quality coaxial cables in the subscriber's premises wiring or poor connections with wall terminals, etc.

(C) Intrusion of unnecessary high-frequency signal components from the commercial power supply at the subscriber's home via the television reception booster or television receiver.

etc. can also be considered. Since these things occur outside the control range of the two-way CATV facility operator, it is extremely difficult for the facility operator to prevent them from occurring.

And due to the intrusion of such unnecessary high frequency signal components,
AG in uplink signal system relay equipment and center equipment.
C functions are inhibited, malfunctions occur in digital data signal processing, etc., and this is a major hindrance to the operation of uplink signal systems, and countermeasures are strongly desired. Also, normally, when signals are brought in from the system, it is done using a branch or distributor as mentioned above, but the upstream signal sending equipment is not connected at the terminal, and only the home television reception booster or television receiver is connected. If connected, there will be impedance mismatch in the upstream signal frequency band, and performance such as reverse coupling loss, inter-terminal coupling loss, branching loss, distribution loss, frequency characteristics, VSWR, etc. of the branch or divider will deteriorate, and There is a risk that the signal system may no longer meet the required performance based on the system design, and countermeasures are strongly desired in this regard as well.

Means for Solving the Problem This invention eliminates unnecessary high-frequency signal components such as those shown in (A) to (C) above between the input section (system side) and the output section (subscriber's home side) of the protector. In order to block signals, at least a first selector is provided that blocks signals in the upstream frequency band, and one of the second selectors passes signals in the frequency band that are blocked by the first selector. The terminal is connected to the input side of the first selector, and the external terminal is terminated to earth using a terminator such as a resistor so as to match the line impedance of the system.

Embodiment FIG. 1 is a circuit diagram showing an embodiment of a protector according to the present invention. The protector has an input terminal 101 and an output terminal 10.
2 is provided, the coaxial cable drawn from the bidirectional CATV system branch or distributor is connected to the input terminal +01, and the coaxial cable drawn into the subscriber's premises is connected to the output terminal! Connected to 02. One terminal of a lightning arrester +05 is connected to the internal conductor side terminal 103 of the input terminal +01, and the other terminal is connected to ground.

Further, one terminal of a fuse 106 is connected to the connection point between the internal conductor side terminal 103 and the lightning arrester 105, and the other terminal is connected to one terminal of a choke coil 107 and a capacitor 108. The terminal is connected to ground. An external conductor side terminal 104 of the input terminal 101 is connected to ground. Capacitor 10 is connected to the other terminal of capacitor 108.
91, I 01I11.112.113 and coil +1
4. The terminal on the life side of the capacitor of the bypass filter (hereinafter referred to as HP F) 117 composed of +15.116 is connected, and the terminal of the capacitor 112 of HPF 117 is connected.
The side terminal is the internal conductor side terminal 11.8 of the output terminal +02.
It is connected to the. An external conductor side terminal +19 of the output terminal 102 is connected to ground via a capacitor 120. Said capacitor 108 and HPF l 17
At the connection point, coils 121, 122, +23.124
, ]25 and capacitors 126, 127, and 128 (hereinafter referred to as LPF).
129's terminal on the coil 121 side is connected, and the coil 12
The terminal on the 4th side uses a resistor as a terminator and connects it to a terminator 130.
is terminated to ground.

The resistance value of the terminator @130 is set to a value equal to the line impedance of the system. CATV is generally 75Ω
It is. For the H'PF 117, constants 109 to 116 are determined so as to pass the downstream signal and block the upstream signal, and constants 121 to 128 are determined for the LPF 129 to pass the upstream signal and block the downstream signal. is determined. The impedance is set equal to the line impedance. As explained above with reference to FIG. 1, in this embodiment, since it is common to set the lower frequency band of the system transmission band for uplink and the upper frequency band for downstream, HPF and LPF are used. However, even if the settings of the uplink and downlink frequency bands are different from those in the above embodiment, the same result can be achieved by changing the combination using a bandpass filter, band elimination filter, etc., as shown in Section 3. can achieve the objectives of

The downstream signal input to the action input terminal 101 is transmitted to the fuse 1.
06, :I passes through the indenser 108, II PFI
+7 is selectively passed through and directed to the output terminal 102. LPF] 29 is set to pass only the upstream signal frequency band, so the downstream signal is 1, P F'
It does not flow into +29. When an unnecessary high frequency signal component in the upstream signal frequency band generated from the subscriber's home is applied to the output terminal +02, II P F l I 7 prevents it from entering the input terminal +01 direction.

On the other hand, since the upstream signal frequency band is terminated by the terminating resistor 130 via the LPF 129, the impedance in the upstream signal frequency band viewed from the input terminal +01 to the output terminal 102 is the system line impedance. It is consistent with

Effects As explained above, the protector according to the present invention can be used as a bidirectional C
If installed in a subscriber's home that does not use the upstream signal system in the ATV system, unnecessary high-frequency signal components generated from the subscriber's home will not intrude into the system's upstream signal system. Since the upstream signal frequency band is matched with the line impedance of the system and terminated, it is possible to maintain ideal operating conditions of branchers and distributors for drawing signals from the system. Therefore, there is no malfunction of relay fusers or center equipment in the uplink signal system, and good two-way CATV operation is possible. The fact that the above-mentioned effect can be achieved within the facility's controlled area is a measure to prevent sink noise that can be reliably carried out at the facility's will, and is very effective.

[Brief explanation of drawings]

FIG. 1 shows an embodiment of the present invention. Reference numeral 27 shows an example of a conventional protector, and FIG. 3 shows another embodiment of the present invention. +01 = input terminal, 102: output terminal, l+7:
Bypass filter (HPF), +29: Low-pass filter (LPF), +30: Termination resistor.

Claims (1)

[Claims] In the line between the input part and the output part, on which the signal is transmitted, there is a first part that blocks signals in the upstream frequency band in bidirectional communication.
a selector is disposed, and on the input side of the first selector, a second selector that passes some or all of the signals in the frequency band blocked by the first selector is provided. A communication protector characterized by being terminated with a terminator.