JP2001111975A - Equipment for catv - Google Patents

Abstract

PROBLEM TO BE SOLVED: To selectively switch a first transmitting signal composed of television broadcasting signal or the like and a second transmitting signal for cable broadcasting composed of an audio signal are to be sent to a terminal side or only the first transmitting signal is to be sent, on the transmission line of a CATV system for transmitting the first and second transmitting signals to the terminal side without making adverse the passing characteristics of respective signals. SOLUTION: An amplifier for two-way CATV system is provided with a down signal switch circuit 22 for switching whether all down signals transmitted from the side of a center device are to be passed through a first route L1 or only the first transmitting signal having a frequency higher than that of the second transmitting signal for cable broadcasting is to be passed through a second route L2. The second route L2 is provided with an HPF 22a for cutting off the second transmitting signal but the second route L2 is grounded when the first route L1 is selected. As a result, when the first route L1 is selected, the HPF 22a becomes a resonance circuit and the passing characteristics of down signals can be prevented from being affected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an F
In addition to the first transmission signal in the same signal form as these broadcast signals in the frequency band used for M broadcast and television broadcast,
CAT in which a second transmission signal for cable broadcasting whose frequency is set lower than the transmission signal is transmitted from the center device to the terminal side
The present invention relates to a CATV device provided on a transmission line of a V system.

[0002]

2. Description of the Related Art Conventionally, a CATV system uses a ground station (broadcasting station) so that a desired broadcasting signal can be selected and demodulated on a terminal side of the system using a commercially available receiver (FM tuner, television receiver, etc.). Station), and transmits a received signal or a broadcast signal for independent broadcast received from the center apparatus to the terminal side with the same frequency allocation as the transmission wave from the ground station. It has been like that.

In recent years, in response to a request from a subscriber to receive a cable broadcast signal from a cable broadcast station that distributes audio signals such as music by wire, transmission signals (such as the FM broadcast and television broadcast) described above have been received. In addition to the first transmission signal, such a transmission signal for cable broadcasting (hereinafter, referred to as a first transmission signal).
A CATV system is also known in which a center signal is transmitted from a center device to a terminal.

[0004] The second transmission signal for such a cable broadcast usually has a transmission frequency lower than the transmission frequency (for example, 26 MHz to 70 MHz) of the first transmission signal (eg, 70 MHz or higher) such as an FM broadcast or a television broadcast. ), A CATV system that transmits a second transmission signal for cable broadcasting to the terminal side in addition to the first signal,
As a CATV device for amplifying, branching, or distributing each of these transmission signals (hereinafter, the first transmission signal and the second transmission signal are collectively referred to as a downlink signal) on a transmission line, the transmission frequency band of the downlink signal is usually More extensive equipment is used.

That is, in a general CATV system device that transmits only the first transmission signal to the terminal, the transmission frequency band of the downlink signal is set to be equal to or higher than the lowest frequency (for example, 70 MHz) of the first transmission signal. However, in a CATV system device that transmits the second transmission signal to the terminal side in addition to the first transmission signal, the transmission frequency band of the downlink signal is set to be equal to or higher than the lowest frequency (for example, 26 MHz) of the second transmission signal. .

[0006]

However, as described above, the transmission frequency band of the downlink signal of the CATV equipment is changed to the second frequency band.
When the transmission signal is expanded to a frequency that can transmit the transmission signal, the transmission frequency band of the second transmission signal includes high-frequency noise generated by home electronic devices and frequencies of transmission radio waves from various wireless devices. In some cases, the signal is mixed into the second transmission signal and transmitted to the terminal side, which may adversely affect the reception / demodulation operation of the downlink signal on the terminal side.

For this reason, in a CATV system that transmits a second transmission signal for cable broadcasting to a terminal in addition to the first transmission signal, a terminal that does not wish to distribute the second transmission signal receives a downlink signal as a downlink signal. It has been desired to be able to selectively transmit only the first transmission signal.

In order to satisfy this requirement, the transmission frequency band of the downstream signal of the CATV equipment such as an amplifier, a branching device, and a distributor is set to a wide band including the second transmission signal, or the second transmission signal is used. What is necessary is just to provide a down signal switching circuit for switching whether to cut off and set a narrow band for passing only the first transmission signal.

By the way, such a down signal switching circuit has
For example, the transmission path of the downlink signal in the CATV equipment is 2
The system is divided into two systems, and either one of the transmission paths can be selected as a transmission path of a downstream signal by a changeover switch, and one path allows only the first transmission signal to pass and blocks the second transmission signal. (For example, a high-pass filter with a cut-off frequency of 70 MHz).

However, when the inventors of the present invention actually manufactured such a downlink signal switching circuit and measured the passing characteristics of the downlink signal in each transmission path,
When a path provided with a high-pass filter (hereinafter, referred to as a second path) is selected, only a first transmission signal can be passed without any problem, but a path for passing all downlink signals without a high-pass filter ( When the first path is selected, a so-called trap in which the transmission loss sharply increases at a specific frequency (for example, around 280 MHz) in the transmission frequency band of the first transmission signal is generated. It was found that one transmission signal could not be transmitted well.

The present invention has been made in view of such a problem, and in addition to a first transmission signal such as a television broadcast signal, a second transmission for cable broadcasting set at a lower frequency than the first transmission signal. On the transmission line of the CATV system that transmits signals to the terminal, both transmission signals are sent to the terminal or
It is an object of the present invention to provide a CATV device capable of selectively switching whether to transmit only the first transmission signal without deteriorating the pass characteristics of each signal.

[0012]

Means for Solving the Problems and Effects of the Invention In order to achieve the above object, in the CATV equipment according to the first aspect, data is transmitted from the center device to the installation point of the equipment via a transmission line. Downstream signal switching means for switching between transmitting the first transmission signal and the second transmission signal to the terminal side or transmitting only the first transmission signal to the terminal side.

The down signal switching means includes a first path through which the first transmission signal and the second transmission signal pass, and a first path through which the first transmission signal and the second transmission signal pass.
A path selection switch for selecting one of a second path provided with a first transmission signal pass filter for passing only the transmission signal and blocking the second transmission signal as a path of a downstream signal; When the first path is selected by the path selection switch, one end or both ends of the second path are grounded to ground or terminated by the transmission impedance of the second path, so that the first transmission signal pass filter is A resonance operation preventing means is provided for preventing the downstream signal passing through the first path from operating as a resonance circuit.

Therefore, in the CATV equipment of the present invention, when the down signal switching means selects the first path as the down signal passing path, the passing characteristic of the down signal on the first path becomes the second path. The first transmission signal passing filter provided on the path side does not deteriorate (in other words, the trap described above does not occur), and all the downstream signals composed of the first transmission signal and the second transmission signal are converted. , Can be transmitted well.

The reason will be described below. First,
As described above, two paths, the first path through which both the first transmission signal and the second transmission signal pass, and the second path through which only the first transmission signal passes, are provided as paths through which the CATV device passes the downstream signal. If one of the two paths is formed and one of the two paths is actually selected as the path through which the downlink signal passes, the transmission loss of the downlink signal on the first path is determined by the transmission frequency of the first transmission signal. The frequency increases sharply at a specific frequency in the band, and the first transmission signal cannot be transmitted well.

Therefore, the inventors of the present application conducted an experiment in order to investigate the cause. As a result, when the first path and the second path were formed in one case constituting the CATV equipment, Since the first path and the second path are arranged close to each other, if the first path is selected as a path for passing a down signal, the first transmission signal pass filter provided on the second path will cause resonance with respect to the first path. It has been found that it works as a circuit and absorbs a part of the downstream signal passing through the first path.

For this reason, according to the present invention, when the first path is selected as the path of the downstream signal via the path selection switch, the second transmission signal passing filter provided on the second path is used as a resonance circuit. In order not to work, the resonance operation preventing means is configured so that one end or both ends of the second path is grounded to the ground or terminated at the transmission impedance of the second path.

Therefore, according to the present invention, when the first path is selected as the path for passing the downstream signal, the first transmission signal pass filter provided on the side of the second path has the characteristic of passing the downstream signal on the first path. The first path is selected as the path through which the downstream signal passes, even if the first path is selected.
Even when a route is selected, it becomes possible to transmit a desired downlink signal to the terminal side satisfactorily.

Here, the resonance operation preventing means only needs to be able to ground or terminate at least one end of the second path when the path selection switch is switched to the side for selecting the first path. It can be configured with a switch for grounding or terminating in conjunction with the switch. However, in order to ground or terminate the second path using such a switch, when the path selection switch is switched to the side that selects the second path, the downstream signal (the first transmission signal) on the second path is used. Only), an expensive switch that can reliably shut off the high-frequency signal when the switch is off must be provided in the switch for grounding or termination so as not to affect the passing characteristics of the switch. In addition, the area of the circuit board must be increased.

Therefore, as the resonance operation preventing means, as described in claim 2, the anode is connected to one end of the second path, the cathode is grounded to ground, and a predetermined current flows in the forward direction to turn on the state. Alternatively, the first impedance is determined by a diode having a predetermined impedance and a path selection switch.
When a path is selected, an energizing circuit may be configured to energize the diode in the forward direction to ground or terminate the second path.

That is, if the resonance operation preventing means is configured as described above, the circuit board may be provided with a diode and a circuit for forming an energizing path of the diode via a path selection switch. The area of the circuit board can be reduced compared to the case of mounting the switch of
It can be realized at low cost.

In order to terminate one end or both ends of the second path by using a diode with the transmission impedance (generally 75 Ω or 50 Ω) of the second path, use a PIN diode whose impedance changes according to a current flowing through the diode. The amount of current flowing through the PIN diode by the means is
What is necessary is just to set the amount of current at which the impedance of the PIN diode becomes the transmission impedance.

On the other hand, the C of the present invention (claims 1 and 2)
The ATV equipment selectively switches between a downlink signal to be transmitted to a terminal and a downlink signal including a first transmission signal and a second transmission signal or only the first transmission signal. Of a CATV device, or by incorporating a downstream signal switching means into various conventionally known CATV devices (for example, a CATV amplifier, a branching device, a distributor, etc.). it can.

For example, when the CATV equipment according to the present invention (claims 1 and 2) is configured as a main line amplifier or a branch amplifier for CATV, the route selection is performed as described in claim 3. A downstream signal amplifier circuit for amplifying a downstream signal passing through the first path or the second path selected by the switch may be provided.

Further, the CATV system not only transmits the downlink signal transmitted from the center device to the terminal, but also
In the case of a CATV system for transmitting an upstream signal transmitted from a terminal to a center device, for example,
As described, the CA according to any one of claims 1 to 3
The TV device may further include a pair of downstream signal passing filters and an upstream signal path including an upstream signal passing filter.

In other words, if the CATV equipment is configured as described in claim 4, the downstream signal input from the terminal connected to the transmission line on the center device side is selectively passed through the downstream signal passing filter. The downstream signal input to the switching means and passing through the downstream signal switching means can be transmitted to the terminal side from another terminal connected to the transmission line on the terminal side via another downstream signal passing filter. Also, the upstream signal transmitted from the terminal side can be transmitted to the center apparatus side via the upstream signal path provided with the upstream signal passing filter.

Thus, according to the CATV equipment of the fourth aspect, in a bidirectional CATV system, a bidirectionally transmitted downlink signal and uplink signal can be satisfactorily passed without interfering with each other. In particular, a pair of upstream signal passing filters are provided in the upstream signal path, and an upstream signal amplifying circuit for amplifying the upstream signal is provided between each of the upstream signal passing filters. For example, a CAT having an upstream signal amplification function
V equipment can be configured.

Further, for example, the CATV equipment according to claim 4 or 5 pulls a branch line branched from a transmission line of a bidirectional CATV system into a building, and transmits the transmission line wired in the building. External bi-directional CAT via line
It is used as a so-called ridged bidirectional CATV device that transmits a down signal from a V system to a terminal device in a building and transmits an up signal sent from the terminal device to an external bidirectional CATV system. In this case, for example, in addition to the downlink signal, a satellite reception signal obtained by receiving a transmission radio wave from an artificial satellite and performing frequency conversion can be transmitted to the terminal side. May be.

In other words, in addition to the downlink signal transmitted from the center device of the external bidirectional CATV system, the bidirectional CATV system in the building is transmitted from the broadcasting satellite (BS) or the communication satellite (CS). There is a type in which a satellite reception signal obtained by receiving a satellite wave can also be transmitted to a terminal. A CATV device used in this type of in-building bidirectional CATV system transmits a satellite reception signal having a higher frequency than a downlink signal and an uplink signal, received by a satellite reception antenna (BS antenna, CS antenna). Must be transmitted to the terminal together with the downlink signal.

Therefore, in the CATV equipment according to the sixth aspect, a down signal and an up signal are passed between a pair of terminals respectively connected to the transmission line on the center device side and the terminal side, and the satellite reception signal is cut off. Through a pair of transmission signal passing filters to connect the downstream signal path and the upstream signal path,
In addition, a satellite reception signal passing filter that passes a satellite reception signal and blocks a downstream signal and an upstream signal is provided in parallel with the path of the downstream signal and the upstream signal formed through the pair of transmission signal passing filters. Connected satellite reception signal path.

Therefore, in the CATV device according to the sixth aspect, not only can the downlink signal and the uplink signal be transmitted bidirectionally, but also the satellite reception signal obtained via a satellite reception antenna or the like can receive other signals. The signal can be separately transmitted to the terminal side without causing interference with the (downlink signal and uplink signal), and can be used very effectively as a device for the above-mentioned in-building bidirectional CATV system.

In the CATV equipment according to the present invention, a pair of satellite reception signal passing filters is further provided in the satellite reception signal path.
If a satellite reception signal amplifying circuit for amplifying a satellite reception signal is provided between the pair of satellite reception signal passing filters, a CATV device having a function of amplifying a satellite reception signal can be configured.

A CAT according to claim 6 or 7.
In a V device, when a downlink signal and a satellite reception signal are configured to be input via one terminal connected to a transmission line on the center device side, an external CAT is connected to this terminal.
The downstream signal transmitted from the V system and the satellite reception signal received by the satellite reception antenna must be mixed by a mixer or the like, and then these signals must be input.

Therefore, the CA according to claim 6 or 7 is preferable.
As the TV device, for example, a satellite reception signal input terminal for inputting a satellite reception signal in addition to a terminal for inputting a downlink signal connected to a transmission line on the center device side as described in claim 8 And the satellite reception signal path may be connected to a satellite reception signal input terminal via a satellite reception signal pass filter.

That is, with this configuration, the downlink signal and the satellite reception signal can be input to different terminals,
Unlike a configuration in which these signals are input to a common terminal, a bidirectional CATV system in a building can be constructed without providing a mixer for mixing a downlink signal and a satellite reception signal.

[0036]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing C of an embodiment to which the present invention is applied.
FIG. 1 is a configuration diagram illustrating the entire configuration of an ATV bidirectional amplifier (hereinafter, simply referred to as an amplifier).

The amplifier of the present embodiment has an external bidirectional CAT
A drop line branched from a transmission line of the V system is pulled into a building such as an apartment or an apartment via a protector or the like, and is connected to an external two-way CATV through a transmission line in the building.
A downlink signal (for example, frequency: 26 MHz to 602 MHz) transmitted from the center device side of the system is transmitted to a large number of subscriber side terminal devices in the building, and an uplink signal transmitted from each terminal device ( For example, the frequency: 650 MHz to 770 MHz) is changed to an external bidirectional C.
Two-way CAT inside the building to send out on the transmission line of the ATV system
In the V system, the signal is provided on a transmission line in a building, and is used to bidirectionally amplify an upstream signal and a downstream signal flowing through the transmission line.

For this reason, the amplifier of this embodiment is provided at the upstream side of the transmission line in the building (in other words, the external bidirectional CAT).
A first input terminal T1 for inputting a downstream signal connected to the center device side of the V system, and a downstream signal output terminal connected to the downstream side of the transmission line in the building (in other words, the terminal device side). An output terminal Tout is provided.

In the amplifier of this embodiment, a satellite reception signal (frequency: 1035 MHz) from a satellite broadcast receiving BS antenna installed on the roof of a building or the like is provided as the satellite reception signal input terminal according to the present invention. A second input terminal T2 for inputting a frequency band of 1 to 1335 MHz, hereinafter referred to as a BS-IF signal) is also provided.

Then, B input to the second input terminal T2
The F-IF signal is taken into an amplifier via an HPF (HPF represents a high-pass filter) 2. HPF
2 is for passing a BS-IF signal and blocking a downstream signal and an upstream signal having a lower frequency than that of the BS-IF signal.
Hz.

The BS-IF that has passed through the HPF 2
The signal is input to an amplifier circuit 4 for amplifying the BS-IF signal, and is amplified by the amplifier circuit 4 to a predetermined signal level. The BS-IF amplified by the amplifier circuit 4
The signal is transmitted to the output terminal Tout via the HPF 6 having the same characteristics as the HPF 2, and is transmitted from the output terminal Tout to the transmission line on the terminal side.

The HPFs 2 and 6 correspond to the satellite signal pass filters according to claims 6 and 7, and the amplifier circuit 4 corresponds to the satellite signal amplifier circuit according to claim 7 and the amplifier circuit 4 is provided. The path between HPF2 and HPF6 corresponds to the satellite reception signal path according to the sixth and seventh aspects.

On the other hand, the upstream signal transmitted from the terminal side is input to an output terminal Tout, and is passed through an LPF (LPF represents a low-pass filter) 10 and an HPF 12.
Captured in the amplifier. The LPF 10 is for passing a downlink signal and an uplink signal and blocking a BS-IF signal, and has a cutoff frequency of, for example, 770 MHz.
z. Also, the HPF 12 is an LPF 10
This is for passing only the upstream signal that has passed through and blocking the downstream signal, and the cutoff frequency is, for example, 6
It is set to 50 MHz.

The upstream signal that has passed through the HPF 12 is input to an amplifier circuit 14 for amplifying the upstream signal, and is amplified by the amplifier circuit 14 to a predetermined signal level.
The upstream signal amplified by the amplifier circuit 14 is supplied to the HPF 1
The signal is transmitted to the first input terminal T1 via the HPF 16 having the same characteristic as that of the LPF 2 and the LPF 18 having the same characteristic as the LPF 10, and is transmitted from the first input terminal T1 to the transmission line on the center device side.

The LPFs 10 and 18 correspond to a transmission signal pass filter according to claim 6, and the HPFs 12 and 16
The amplifying circuit 14 corresponds to the upstream signal pass filter according to claims 4 and 5, and the HPF 1 provided with this upstream signal amplifier circuit.
The path between the 2-HPF 16 corresponds to the upstream signal path according to claims 4 and 5.

Next, a downlink signal transmitted from an external bidirectional CATV system center device is input to the first input terminal T1, and this downlink signal is transmitted to a ground station (broadcasting station) on the center device side. ) And a transmission signal (first transmission signal) of a predetermined frequency band (for example, 70 MHz to 602 MHz) obtained by receiving broadcast waves of FM broadcast and television broadcast transmitted from the first transmission signal. And a cable broadcast signal (second transmission signal) from a cable broadcast station set to a low frequency (for example, 26 MHz to 70 MHz).

Then, the downstream signal input to the first input terminal T1 is taken into the amplifier via the LPF 18 and the LPF 20. The LPF 20 is for passing only a downstream signal and blocking an upstream signal and a BS-IF signal, and has a cutoff frequency of, for example, 602 MHz.
Is set to

The downstream signal passing through the LPF 20 is
The DC signal component is cut off and the signal is input to a downstream signal switching circuit 22 as a downstream signal switching unit via a capacitor C1 that allows the downstream signal component (high-frequency signal component) to pass. The downstream signal passing through the downstream signal switching circuit 22 is input to the downstream signal amplifier circuit 24 via the capacitor C2 provided for the same purpose as the capacitor C1,
Further, the downstream signal amplified by the amplifier circuit 24 is LP
LPF 26 having the same characteristics as F20 and LPF 1 described above.
0 to the output terminal Tout and output terminal Tout
out is sent out on the transmission line on the terminal side.

The LPFs 20 and 26 correspond to the downstream signal pass filter according to the fourth aspect, and the amplifier circuit 24 corresponds to the downstream signal amplifier circuit according to the third aspect. Next, the downstream signal switching circuit 22 sends the downstream signal composed of the first transmission signal and the second transmission signal to the amplifier circuit 24 side (in other words, the terminal side), or, among the downstream signals, for cable broadcasting. The user selects whether the second transmission signal is cut and only the first transmission signal is transmitted to the amplifier circuit 24 (terminal side) by the path selection switch SW.
Can be arbitrarily set by manually operating the system, and is configured as follows.

That is, the path selection switch SW includes a fixed contact s1 for signal input connected to the downstream signal input path on the capacitor C1 side and a fixed contact for signal output connected to the downstream signal output path on the capacitor C2 side. s2, fixed contacts t1 and t2 connected to each other via a first path L1 for directly passing the downstream signal, and a second path for passing the first transmission signal and blocking the second transmission signal among the downstream signals. Fixed contacts u1 and u2 connected to each other via L2,
Sliding contact v that is slid by user's switch operation
1 and v2, the fixed contacts s1 and s2 and the fixed contact t
1 and t2, or fixed contact s1,
Whether to connect s2 and the fixed contacts u1 and u2, respectively, can be manually switched.

The second path L for interrupting the second transmission signal
2 is provided with an HPF 22a whose cut-off frequency is set to, for example, 70 MHz, as a first transmission signal passing filter. This HPF 22a converts a downstream signal passing through the second path L2 into only the first transmission signal. Has restricted.

The HPF 22a and the fixed contact u1 corresponding to the fixed contact s1 for signal input are directly connected, but the HPF 22a and the fixed contact s for signal output are connected.
2 is connected to the fixed contact u2 via a capacitor Co that cuts off a DC signal component and passes a downstream signal component (here, a first transmission signal). And HPF
22a to the connection point with the capacitor Co (in other words, HPF
The anode of a diode Do whose cathode is grounded is connected to one end of the first transmission signal output side 22a).

The diode Do is turned on by being supplied with electricity in the forward direction, and grounds the second path L2 provided with the HPF 22a to the ground (corresponding to the resonance operation preventing means of the present invention). Yes, for example, PI
It is composed of N diodes. When the path selection switch SW is connected to the fixed contacts s1 and s2 and the fixed contacts t1 and t2, respectively, the first path L1 is selected as a path for passing the down signal, and the diode Do is forward-directed. The connection point of the HPF 22a with the capacitor Co is connected to the first path L1 via the resistor Ro so that a current flows, and the path between the fixed contact S2 and the capacitor C2 is connected via the resistor R1. , A power supply voltage Vc (positive DC voltage) is applied.

As a result, when the path selection switch SW selects the first path L1 as the path for passing the down signal, the resistance R1 → the fixed contact s2 → the fixed contact t2 → the resistance R
o, a forward current is supplied from the DC power supply to the diode Do through the path of o (corresponding to the energizing circuit according to claim 2), and the diode Do is turned on, and the HPF 2
The second path L2 provided with 2a is grounded.

The resistors Ro and R1 are for limiting the current flowing through the diode Do, and are provided with a capacitor C1.
o indicates that when the path selection switch SW is selecting the second path L2 as a path through which the downstream signal passes, the diode D
This is for preventing a current from flowing through o.

As described above, in the amplifier according to the present embodiment, the LPF 2 that allows the downstream signal to pass through the amplifier is used.
A down signal switching circuit 22 is provided on the down signal path between 0 and 26, and by manually operating a path selection switch SW provided in the down signal switching circuit 22, all signals are output from the output terminal Tout to the terminal side. It is possible to arbitrarily set whether to transmit the downlink signal (the first transmission signal and the second transmission signal) or to transmit only the first transmission signal.

For this reason, there is no need to provide a cable broadcasting service comprising audio signals such as music, etc.
In the system, the path selection switch SW is set to HPF
By switching to the side that selects the second path L2 provided with 22a, noise having the same frequency as the frequency band of the second transmission signal (cable broadcasting signal) is transmitted to the terminal device of the in-building bidirectional CATV system. Can be prevented, and the transmission quality of the downstream signal in the in-building bidirectional CATV system can be improved.

An HPF 22a is provided in the second path L2 for passing only the first transmission signal out of the downlink signals in order to block the passage of the second transmission signal. When the first path L1 is selected, the diode Do is energized to ground the second path L2 to the ground.
Function as a resonance circuit, and can prevent the transmission characteristic of the first transmission signal on the first path L1 from being adversely affected.

Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment.
Various embodiments can be adopted. For example, in the above embodiment, the downstream signal switching circuit 22 is connected between the LPF 20 through which only the downstream signal passes in the amplifier and the downstream signal amplifying circuit 24.
Provided, but the down signal switching circuit 22
May be provided at any position on the path through which the downstream signal passes in the amplifier. As shown in FIG. 2, between the LPF 18 where the downstream signal and the upstream signal flow in both directions, and the HPF 16 and the LPF 20. May be provided on the route. In this case, the signal input / output terminals of the downstream signal switching circuit 22 are connected to the DC component blocking capacitors C1 and C
It is necessary to provide 2.

Further, in the above embodiment, in the downstream signal switching circuit 22, a diode Do is provided at one end of the HPF 22a constituting the second path L2 on the output terminal Tout side, and a current is caused to flow through the diode Do so that the current flows through the diode Do. Output terminal Tout
Although it has been described that one end of the side is grounded, for example, FIG.
, A diode Do may be provided at one end of the HPF 22a on the first input terminal T1 side, and a current may flow through the diode Do to ground one end of the second path L2 on the first input terminal T1 side, or , HP configuring the second path L2
Diodes Do may be provided at both ends of F22a, and both ends of the second path L2 may be grounded by passing a current through both diodes Do.

Next, in the above embodiment, when the path selection switch SW is switched to the side through which all the down signals pass, a current flows through the diode Do via the resistor R1, the path selection switch SW and the resistor Ro. Diode Do
Is turned on, and one end of the second path L2 is grounded to the ground.
When an N diode is used, the impedance of the diode Do becomes the transmission impedance (for example, 75Ω) of the second path L2 when a current flows through the diode Do by adjusting the resistance values of the resistors R1 and Ro. , One end or both ends of the second path L2 may be terminated.

That is, since the impedance of the PIN diode changes depending on the amount of current flowing therethrough, the resistor R which determines the amount of current flowing through the diode Do so that the impedance becomes the transmission impedance of the second path L2.
By setting the resistance values of 1 and Ro, one end or both ends of the second path L2 can be terminated when the path selection switch SW is switched to the side that allows all the down signals to pass.

Even if one end or both ends of the second path L2 is terminated in this way, it is possible to prevent the HPF 22a from operating as a downstream signal resonance circuit. on the other hand,
In the above embodiment, the second input terminal T2 for inputting the satellite reception signal (BS-IF signal) from the BS reception antenna.
And the BS-IF input to the second input terminal T2
The amplifier configured to amplify the signal in the amplifier circuit 4 and then send the signal from the output terminal Tout to the terminal has been described. For example, the second input terminal T2 is deleted, and the HPF2
Is connected to the first input terminal T1 instead of the second input terminal T2, the BS-IF signal is amplified by the amplifier circuit 4 and transmitted from the output terminal Tout to the terminal side. Can be.

That is, when only the first input terminal T1 is used as the input terminal, the downstream signal and the BS-IF signal may be mixed and input to the first input terminal T1. In this case, although a separate mixer for mixing the downlink signal and the BS-IF signal is required, the BS-IF signal is separately provided.
The IF signal is input to the amplifier circuit 4 via the HPF 2,
The downstream signal is input to the downstream signal switching circuit 22 via the LPF 18 and the LPF 20, and since these input signals do not interfere with each other, an amplifier having the same signal transmission characteristics as the above embodiment can be configured.

In particular, if it is not necessary to amplify a satellite reception signal such as a BS-IF signal, the amplifier circuit for amplifying the satellite reception signal may be omitted from the amplifier of the above embodiment. If it is not necessary to pass a satellite reception signal such as an IF signal, the second input terminal T2, HPF2, amplifier circuit 4, and HPF6 may be deleted from the amplifier of the above embodiment.

On the other hand, the amplifier of the above embodiment is a bidirectional CA
For a TV system, the down signal and the up signal transmitted bidirectionally in this system have been described as being amplified and sent to the terminal side or the center apparatus side. If only one or both passes, the unnecessary amplifier circuit 14 or 24 may be deleted from the amplifier of the above embodiment.

Further, a CAT transmitting only a downlink signal
In the V system, from the amplifier of the above embodiment, the second input terminals T2, HPF2, amplifying circuits 4, and HPF6 for transmitting satellite reception signals, and the LPFs 18, for transmitting upstream signals,
HPF 16, amplifying circuit 14, HPF 12, and LPF 1
And 0 are all removed, and an amplifier having only a downstream signal transmission circuit may be used. Further, if there is no need to amplify the downstream signal, the downstream signal amplification amplifier circuit 2 may be used.
It is sufficient to configure a transmission device for downlink signal switching in which 4 is also deleted.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating a configuration of an amplifier for a bidirectional CATV system in a building according to an embodiment.

FIG. 2 is a circuit diagram showing a modified example of the in-building bidirectional CATV system amplifier of the embodiment.

[Explanation of symbols]

T1 first input terminal, T2 second input terminal, Tout output terminal, 2, 6, 16, 12, 22a HPF (high-pass filter), 10, 18, 20, 26 ... LPF (low-pass filter), 4 , 14, 24 ... amplifier circuit, 22 ... down signal switching circuit, SW ... path selection switch, L1 ... first
Path, L2: second path, Ro, R1: resistance, Co, C
1, C2: capacitor, Do: diode.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5C064 BA01 BB05 BC12 BC13 BC16 BD01 BD07 5K046 AA01 BA05 BB03 CC00 CC06 CC22 CC28 KK03 KK13 PP05

Claims (8)

[Claims] 1. A first transmission signal having the same signal form as each of these broadcast signals in a frequency band used for FM broadcasting and television broadcasting using a ground station, and a frequency set lower than the first transmission signal. The second transmission signal for cable broadcasting is a CATV signal transmitted from the center device to the terminal side as a downlink signal.
The first transmission signal and the second transmission signal, which are provided on a transmission line of a system and transmitted from the center device to the installation point via the transmission line, are sent to a terminal, or the first transmission signal CATV equipment provided with a down signal switching means for switching whether only the signal is transmitted to the terminal side, wherein the down signal switching means comprises: a first path through which the first transmission signal and the second transmission signal pass; A second path provided with a first transmission signal pass filter for passing only the first transmission signal and blocking the second transmission signal; and a first path and a second path for passing the down signal. A path selection switch for selecting one of the paths, and, when the first path is selected by the path selection switch, whether one end or both ends of the second path is grounded to ground. Or a resonance operation preventing means for terminating at the transmission impedance of the second path to prevent the first transmission signal pass filter from operating as a resonance circuit for a downstream signal passing through the first path. CATV equipment comprising: 2. The resonance operation preventing means includes: a diode having an anode connected to one end of the second path, a cathode grounded to ground, and turned on or having a predetermined impedance when a predetermined current flows in a forward direction; When the first path is selected by the path selection switch, the diode is energized in a forward direction, and the second path is selected.
The CATV device according to claim 1, further comprising: an energizing circuit that grounds or terminates a path. 3. The apparatus according to claim 1, further comprising a downstream signal amplifying circuit for amplifying the downstream signal passing through the first path or the second path selected by the path selection switch.
Or the CATV equipment according to claim 2. 4. The bidirectional CATV system according to claim 1, wherein the CATV system transmits the downlink signal to the terminal via the transmission line and transmits an uplink signal transmitted from the terminal to the center device. The CATV equipment is further provided between a pair of terminals respectively connected to the transmission lines on the center device side and the terminal side and the down signal switching means, and passes the down signal, A pair of downstream signal passing filters for blocking the upstream signal, and provided in parallel with a downstream signal path formed between the pair of terminals via the pair of downstream signal passing filters;
The CATV device according to any one of claims 1 to 3, further comprising: an upstream signal path including an upstream signal passing filter that passes the upstream signal and blocks the downstream signal. 5. The method according to claim 1, wherein a pair of the upstream signal passing filters is provided in the upstream signal path, and an upstream signal amplifying circuit for amplifying the upstream signal is provided between the pair of upstream signal passing filters. The CA according to claim 4, characterized in that:
TV equipment. 6. The terminal for CATV receives, in addition to the downlink signal, a satellite reception signal having a higher frequency than the downlink signal and the uplink signal obtained by receiving and transmitting a radio wave transmitted from an artificial satellite. Between the pair of terminals respectively connected to the transmission line on the center device side and the terminal side, a pair of transmission signals for passing the downlink signal and the uplink signal and blocking the satellite reception signal. The downlink signal path and the uplink signal path are connected through a pass filter, and the satellite is connected in parallel to the downlink signal and uplink signal paths formed through the pair of transmission signal pass filters. 5. A satellite reception signal path having a satellite reception signal passing filter for passing a reception signal and blocking the downstream signal and the upstream signal is connected. The CATV equipment according to claim 5. 7. A satellite reception signal pass filter is provided in the satellite reception signal path, and a satellite reception signal amplifying circuit for amplifying the satellite reception signal is provided between the pair of satellite reception signal pass filters. The CATV device according to claim 6, wherein the CATV device is used. 8. A satellite reception signal input terminal for inputting the satellite reception signal, wherein the satellite reception signal path is connected to a transmission line on the center device side via the satellite reception signal pass filter. The CAT according to claim 6 or 7, wherein the CAT is connected to the satellite reception signal input terminal instead of the terminal.
V equipment.