JPH05304672A - Inflow noise preventing circuit - Google Patents

Abstract

PURPOSE:To prevent the inflow of noise by providing a switch enterring an HPF passing the only outgoing signal, an LPF passing the only incoming signal, and an incoming return signal to the LPF only at the time of the incoming signal transfer. CONSTITUTION:A call signal passes through an HPF 13 of an inflow noise preventing circuit 1 in the outgoing area and a HPF 21 of a CATV converter 2 to be received by a CPU 25. The CPU 25 operates an RF switch 15 to 'pass' it. Then the data bit string is sent to a center device through a MODEM 24. In this case, as this signal is in the frequency of incoming band, it is sent through an LPF 14 to a CATV line 3. In this case, the noise from the other terminal, thereby the inflow of noise to a line 3 is evaded and the inflow noise is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ingress noise prevention circuit used in a CATV system, and more particularly to a circuit for preventing inflow of household noise in an upstream signal of the CATV system.

[0002]

2. Description of the Related Art Generally, a CATV system transmits TV broadcasts such as VHF and UHF from a center device side to a terminal side via a CATV line (downward direction),
Conversely, if a scrambled image is flowing from the terminal side to the center device side, a scramble release signal is sent, and a security sensor (fire detector,
When a security sensor or the like) is connected, so-called bidirectional transmission is performed in which a signal of security information or the like is returned (upstream direction). In this case, since the CATV system has a tree-like configuration with the center device side as the apex, even if the so-called polling method of calling a specific terminal is adopted, noise generated in each terminal is transmitted to the center device side. There is a problem that a so-called inflow noise phenomenon is generated, which prevents normal transmission of signals in the upstream direction.

On the other hand, in the conventional CATV system, all the branch amplifiers at each stage are controlled so that only the signal from a specific terminal reaches the center device side, and the upstream signal from the other direction is suppressed. The ingress noise was prevented.

[0004]

However, in such a conventional CATV system method, a specific terminal is called by polling, and at the same time, a good line is passed through all the branch amplifiers of each stage through an upstream signal. There is a problem in that it is necessary to specify and control, and it is necessary to perform very complicated control to judge the route individually over all terminals.

Further, the complexity of this control not only prolongs the time required for one polling, but also requires a complicated circuit configuration and processing on both the center device side and the amplifier side, resulting in a decrease in reliability and cost. It was also the cause of the up.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and provide a circuit for preventing ingress noise without performing complicated system control.

[0007]

In order to achieve the above object and to solve the conventional problems, the ingress noise prevention circuit according to the present invention performs communication between a center device and a terminal provided in each home system. In a directional communication CATV system, a high-pass filter that is inserted in series with the communication line of the CATV system and the connection part of each home system in series with the communication line and passes only the signal in the downlink band sent from the center device side to each terminal ( H.P.F.), a low-pass filter (L.P.F.) which is arranged in parallel with the high-pass filter and passes only an upstream band signal returned from the terminal side to the center device side, and the low-pass filter. And a changeover switch connected in series to control the signal input to the low-pass filter.

Further, the invention of claim 2 is characterized in that the change-over switch is operated by a command of a bidirectional terminal connected to the CATV system terminal side.

Further, the invention of claim 3 is a protector for CATV, which comprises a high-pass filter (HP) for passing only signals in the downlink band sent from the center device side to each terminal, and A low-pass filter (LPF) that passes only signals in the upstream band returned from the terminal side to the center apparatus side, which are arranged in parallel with the high-pass filter.
And a changeover switch that is connected in series with the low-pass filter and controls a signal input to the low-pass filter.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an embodiment of a system using an ingress noise prevention circuit according to the present invention. Here, 1 is an ingress noise prevention circuit, 2 is a CATV converter installed in a house, 3 is a CATV line, and 4 is a CATV line.
Is a home system, and 6 is a protector.

In the CATV system, the main-stream ingress noise prevention circuit 1 uses the low-pass filter that passes only the signal in the upstream band (10 to 50 MHz) used for upstream data transmission to transmit upstream data. This is a circuit that prevents ingress noise during transmission. Generally, as shown in FIG. 2, the home system 4 and the CATV line 3 are connected.
It is provided inside the so-called protector 6, which is installed at the boundary with the. This ingress noise prevention circuit 1 is
An up-side terminal 11 connected to the line 3, a down-side terminal 12 connected to the home system 4, a high-pass filter 13 provided between both terminals and connected in series with the CATV line 3, and similarly to the CATV line. 3, a low pass filter 14 connected in series with the high pass filter 13 and an RF switch (changeover switch) 15 connected in series with the low pass filter 14. In addition, a lightning protection element 16 and a coil 17 and capacitors 18 and 19 are provided as a filter for passing DC and low frequency signals.

On the other hand, in the home system 4, the CATV converter 2 is connected to the terminal 5. The CATV converter 2 is for viewing a multi-channel program on a general television by converting a CATV program consisting of several tens of channels into one channel or two channels and outputting a video signal. It also has a function as an interactive terminal. The CATV converter 2 according to the present invention is a TV converter unit such as a tuner or an intermediate frequency amplifier for demodulating a television signal sent through the CATV line 3 and outputting the television signal to a television or the like, like a normal CATV converter. In addition to including 40, a high-pass filter 21, an RF amplifier 22, an RF switch 23,
Modulator 24, demodulator 27, central processing unit (hereinafter abbreviated as CPU) 25 for controlling these, I / O
26 are provided.

Here, the high-pass filter 13 of the ingress noise prevention circuit 1 is a downlink band (70 to 450 MHz) used for a television signal sent from the center device side.
It is a circuit that passes only the signal of. That is, the television signal sent from the center device side passes through the high-pass filter 13 and flows into the home system 4.
On the contrary, the upstream band signal cannot pass through the high pass filter 13 including noise. On the other hand, the low-pass filter 14 is a circuit that passes only signals in the upstream band of 10 to 50 MHz. That is, as a result, in data transmission in the upstream direction, signals outside this band are removed as noise.

Next, the RF switch (changeover switch) 15
Is a switch that operates by a DC signal from the outside, and controls the opening and closing of the circuit on the low-pass filter 14 side.
That is, when this is turned on during upstream data transmission, the return signal from the home system 4 side flows through the low-pass filter 14, and this signal is transmitted to the center device side via the CATV line 3. Therefore, conversely, when the RF switch is OFF, the signal in the upstream band does not flow to the CATV line 3 side including noise. In this case, the RF switch 15 is controlled by the control signal from the CATV converter 2. As the RF switch 15, a switch that can be operated from the outside such as a relay is used. As the configuration, a circuit arranged in series with the circuit on the side of the low-pass filter 14 to directly open and close the circuit, or a branch is provided and connected to the ground to connect the signal to the ground.
The data transmission in the upstream direction may be controlled depending on whether or not the data is dropped to the destination. However, in the latter case, when the RF switch 15 is closed and connected to the ground, the down signal that has passed through the high-pass filter 13 falls to the ground via the RF switch 15 and is not output to the home system 4. In order to prevent this, it is necessary to use two low-pass filters 14 with the RF switch 15 interposed therebetween. On the other hand, in the former case, only the low-pass filter 14 on the left side in FIG. In addition, this RF switch 15
In some cases, since the capacitor 19 is provided in the preceding stage, the high frequency signal is actually turned on / off.

On the other hand, the high-pass filter 21 in the CATV converter 2 also passes only the signal in the downlink band as described above, and specifically passes the ringing signal sent by polling from the center device side. Also,
The RF switch 23 is controlled by the CPU 25, and C
It is turned on when the PU 25 sends a return signal in the upstream band in response to polling from the center device side. The RF amplifier 22 is a circuit that amplifies the returned signal.

Next, the operation of this embodiment will be described with reference to FIG. CATV that normally performs bidirectional transmission
In the system, a television signal is transmitted from the center device side at a downlink band frequency. In addition to this, a call signal for calling each terminal by a so-called polling method is also sent in this band. Further, in each terminal, the CATV converter 2 receives this calling signal, and when its own address is designated, the requested data is returned to the center device side.

Now, assume that the terminal to which the CATV converter 2 is connected is designated. At this time, since the ringing signal is sent in the downlink band, the ingress noise prevention circuit 1
The high-pass filter 13 and the high-pass filter 21 of the CATV converter 2 are received by the CPU 25. The CPU 25 returns the requested data based on the information of this signal to the center device side this time with the frequency of the upstream band.

At this time, the CPU 25 first outputs a DC signal via the I / O 26. RF by this DC signal
The switch 15 is activated to "pass". Next, CA
A command is also issued to the RF switch 23 in the TV converter 2 to make it "pass". Then, after that, the data bit string is transmitted to the center device side via the modem 24. In this case, since this signal has a frequency in the upstream band, it passes through the low-pass filter 14 and is sent to the CATV line 3. At this time, the noise from the other home system is cut by the function of the circuit provided in the other home system. As a result, mixing of noise into the CATV line 3 is avoided, and merge noise is prevented.

After this return is completed, the CPU 25 again issues a command to turn off the RF switches 15 and 23.
That is, the upstream band signal does not flow out of the home-side system 4 on the CATV line 3 side. Therefore,
Even when the terminal of another home side system is responding, the noise generated in the home side system 4 is not mixed in the signal in the upstream band.

As described above, in this embodiment, the inflow noise prevention circuit 1 is provided in the protector 6, but the mounting position is not limited to this. For example, the protector 6 alone is provided. Of course, it may be inserted between the home system 4 and the home system 4. Further, in the present embodiment, a system in which each terminal is called by the polling method is assumed, but C
The present invention can be achieved by other methods such as SMA / CD. Further, in this embodiment, the CATV converter is installed inside the home.
Although it is configured to use the computer 2, the terminal is CATV.
Not limited to the converter, any type may be used as long as bidirectional communication is possible.

[0021]

As described above, in the ingress noise prevention circuit according to the present invention, the high-pass filter that passes only the downlink band signal, the low-pass filter that passes only the uplink band signal, and the terminal are By providing a changeover switch that inputs the return signal of the upstream band to the low-pass filter only when transmitting the signal in the upstream direction, not only blocking the noise of the home system of the terminal at the time of sending the return signal, but also other home systems There is an effect that it is possible to prevent the noise from flowing in. Therefore, the normal transmission of the upstream signal due to the ingress noise can be achieved without performing complicated control.

In particular, according to the second aspect of the present invention, since the changeover switch is controlled by a command from the bidirectional terminal connected to the designated terminal, the present invention can be performed only by calling the terminal by polling or the like. There is an effect that the circuit can be controlled. Therefore, inflow noise prevention can be used with simpler control, and reliability can be improved and cost can be reduced.

Further, according to the invention of claim 3, by installing the circuit in the protector, installation, maintenance,
This has the effect of facilitating inspections, etc., and also making the protector itself multifunctional. Therefore, the cost can be reduced by saving labor such as installing circuits and saving space.
The product value of the protector itself can also be increased.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of an ingress noise prevention circuit according to the present invention.

FIG. 2 is a block diagram showing an installation example of a protector including an ingress noise prevention circuit according to the present invention.

[Explanation of symbols]

 1 ingress noise prevention circuit 2 CATV converter (two-way terminal) 3 CATV line 4 home system 6 protector 13 high-pass filter 14 low-pass filter 15 RF switch (changeover switch)

Claims (3)

[Claims] 1. A two-way communication CATV system for performing communication between a center device and a terminal provided in each home system, wherein a communication line of the CATV system and a connection portion of each home system are inserted in series to the communication line. And a high-pass filter (HPF) that allows only the signals in the downlink band sent from the center device side to each terminal to pass through, and the uplink that is sent from the terminal side arranged in parallel to the high-pass filter to the center device side. Ingress noise prevention, comprising: a low-pass filter (LPF) that passes only a band signal, and a changeover switch that is connected in series to the low-pass filter and that controls a signal input to the low-pass filter. circuit. 2. The ingress noise prevention circuit according to claim 1, wherein the changeover switch is activated by a command from a bidirectional terminal connected to the CATV system terminal side. 3. A two-way CATV system for performing communication between a center device and a terminal provided in each home system, wherein a communication line of the CATV system and a connection part of each home system are installed in series with the communication line. And a high-pass filter (HPF) that allows only the signals in the downlink band sent from the center device side to each terminal to pass through, and the uplink that is sent from the terminal side arranged in parallel to the high-pass filter to the center device side. A low-pass filter (LPF) that allows only signals in a band to pass through, and a ingress noise prevention circuit that includes a changeover switch that is connected in series to the low-pass filter and that controls a signal input to the low-pass filter. Characteristic protector.