JP2003199068A - Booster - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a booster applicable to a community transmission channel such as a CATV system, which is capable of reducing production cost with a simple constitution while improving transmission characteristics by suppressing insertion losses during signal pass. <P>SOLUTION: A signal pass circuit forming the booster has a constitution in which, roughly speaking, a signal amplifier APa section provided with amplifiers AMP1, AMP2 and a gain controller GC and a signal attenuating section ATa provided between the following stage of the section APa and provided with a plurality stages of attenuators ATT are connected in series between an input terminal IN and an output terminal OUT. After being amplification-processed by the former section APa so as to obtain a prescribed gain, an input signal is attenuation-processed to cancel the gain by the latter section ATa, and is outputted as an output signal. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a booster,
In particular, the present invention relates to a booster suitable for use in a co-listening transmission line such as a cable television system.

[0002]

2. Description of the Related Art Conventionally, as a communication means in a large-scale new town where a large number of detached houses are lined up, a complex new town including a group of apartments, or a local city, a plurality of people in a predetermined area or a residential building are used. A two-way system that connects a dwelling unit and a cable TV (hereinafter abbreviated as "CATV") center station through a co-listening transmission path (for example, an optical / coaxial transmission cable network) and bidirectionally transmits information and signals. CATV systems are known.

In recent years, such bidirectional CAT
Using the V system, in addition to the CATV system's original request for TV broadcasting and distribution services, fire and gas leaks from the security sensor installed in each dwelling unit,
A centralized monitoring type security service that collects various information regarding the occurrence of abnormal situations such as intrusion of suspicious persons and centrally manages it at the CATV center station side, and information communication terminals such as personal computers installed in each dwelling unit at the CATV center station A communication connection service for transmitting and receiving various kinds of information by connecting to an electric communication network such as the Internet or a public telephone network via the Internet has come to be provided.

Here, the signal transmitted through the common listening transmission line laid between each dwelling unit and the CATV center station is
Specifically, as shown in FIG. 5, approximately 10 to 55 MHz
Set the frequency band of the
Request signals are sent to the TV center station, and information provided via the Internet is transmitted and received. On the other hand, a frequency band of approximately 70 to 770 MHz is set for the downlink, and a television for about 100 channels is set. A broadcast signal (for example, a VHF broadcast signal, a UHF broadcast signal, etc.) is transmitted. The request signal, the Internet information, and the like are transmitted as signals transmitted and received through the co-listening transmission path with reference to a frequency width of 6 MHz assigned to a television broadcast signal for one channel.

Further, in general, boosters for amplifying signals with a predetermined gain are installed everywhere in the path of the co-listening transmission line in order to compensate for the transmission loss of the signal in the co-listening transmission line of the CATV system. Here, the schematic circuit configuration of the booster in the conventional technology is, for example, as shown in FIG. 6, the downlink side amplification function unit APd and the uplink line amplification function unit APu are arranged in parallel via the demultiplexing mixer Ds. It has a connected configuration. Further, the amplifier function unit APu on the upstream side is connected to the amplifier AM via high frequency relays RLa and RLb.
A signal amplification path (signal amplification circuit) to which P is connected and a signal path path (signal path circuit) consisting of only the signal line Lp are provided in parallel, and further drive power to the amplifier AMP and the high frequency relays RLa and RLb is supplied. The switch SWp for switching and controlling the supply is provided.

In such a conventional configuration, the switch S
The signal amplification path (amplifier AMP) is selected as a signal path on the upstream side by switching the Wp to control the supply state of the driving power to the amplifier AMP and the high frequency relays RLa and RLb. Signal amplification function (switch SWp
Is when the contact Na is connected) and the signal path route (signal line L)
The signal path function (when the switch SWp is connected to the contact Nb) and the amplifier A
A signal cut function (switch SWp) that cuts off the supply of drive power to both the MP and the high frequency relays RLa and RLb to stop the function of the amplification function unit APu on the upstream side and cuts off the output of the signal based on the input signal. Is when contact Nc is connected)
Either of these can be selectively set.

Therefore, in designing and constructing the co-listening transmission line of the CATV system, the function (either the signal amplifying function, the signal path function or the signal cutting function) required in the co-listening transmission line is singled out. It can be easily realized by applying the booster and switching the switch. The configuration of the bidirectional booster (amplifier) as shown in FIG. 6 is disclosed in, for example, Japanese Patent Laid-Open No. 2000-1970.
It is described in detail in Japanese Patent Publication No. 19 and the like.

[0008]

However, the booster having the above-mentioned structure has problems such as deterioration of the transmission characteristics as described below. That is, considering the signal characteristics when the switches are operated to switch the signal paths to realize the above functions, when the signal amplification function is selected and set, as shown in FIG.
As shown in (a), an input signal of the uplink having a frequency band of about 10 to 55 MHz is amplified by a predetermined gain set in the amplifier AMP (in the figure, a case of a gain of 30 dB) is amplified and output. Further, when the signal cut function is selectively set, the transmission path of the input signal is cut off as shown in FIG.
A signal having a V level is output. On the contrary,
When the signal path function is selected and set, the signal line L
As shown in FIG. 7C, the transmission loss at p or the filter loss (insertion loss) due to the filter inserted in the common listening transmission path causes an attenuation of several dB with respect to the original level of the input signal. There was a problem that the output signal was output.

Here, in the co-listening transmission line which constitutes the CATV system, generally, a tree-and-branch in which a large number of branch lines are sequentially branched and distributed from a small number of trunk lines to a dwelling unit which is a service target of CATV. Since the network of the system is adopted, the signals transmitted from each dwelling unit to the CATV center station on the upstream line are concentrated from a large number of branch lines to a small number of trunk lines in sequence, so that the dwelling units in each dwelling unit and the common listening transmission line are connected. The effect of so-called ingress noise, which is the addition and amplification of various types of noise generated on the way, becomes great, and the CN ratio (carrier to noise rati) of the network is increased.
o: Carrier-to-noise ratio) is significantly deteriorated. Therefore, when designing and constructing a co-listening transmission line by applying the booster as described above, noise generated in the uplink is reduced as much as possible, and
It was necessary to take measures to maintain good signal gain.

Further, in the booster as described above,
When the signal amplification path and the signal path path are formed on the same substrate, noise generated on the signal amplification path side (amplifier noise) is obtained by electrically separating both signal paths (by taking isolation). ) Need not be mixed into the signal path route side. For example, as shown in FIG. 6, a configuration in which a high frequency relay or the like is interposed in the signal route is applied. In this case, the booster There is a problem that the circuit configuration becomes large and the product cost rises.

In view of the above problems, the present invention is a booster applied to a co-listening transmission line of a CATV system or the like, and has a simple circuit configuration to suppress insertion loss at the time of signal path. An object of the present invention is to provide a booster capable of reducing the product cost while improving the transmission characteristics.

[0012]

A booster according to a first aspect of the present invention has at least a signal amplifying function for amplifying an input signal so as to have a predetermined gain, and passing the input signal as it is. In a booster having a signal path function to perform, a signal amplification unit that amplifies the input signal so as to have a predetermined gain, and an amplification process that is provided after the signal amplification unit and is performed by the signal amplification unit. It is characterized by including a signal path circuit including a signal attenuator for attenuating the gain of the signal obtained.

The booster according to a second aspect is the booster according to the first aspect, wherein the signal path circuit is such that the gain given to the signal in the signal amplifying section is a gain attenuation processing in the signal attenuating section. It is characterized by being set to be offset by. A booster according to a third aspect is the booster according to the first or second aspect, wherein the signal attenuating section has a configuration in which a plurality of attenuators are connected in series.

A booster according to a fourth aspect is the booster according to any one of the first to third aspects, wherein the booster selectively outputs at least the output signal of the signal amplifying section and the output signal of the signal attenuating section. It is characterized by having a changeover switch for changing over and outputting. The booster according to claim 5 is the booster according to any one of claims 1 to 4, wherein the booster is a signal that cuts off an output of a signal based on the input signal by switching the changeover switch. It is characterized by having a cut function. A booster according to a sixth aspect is the booster according to any one of the first to fifth aspects, characterized in that the booster is installed in a co-listening transmission path that constitutes a cable television system.

That is, the booster according to the present invention has a signal path circuit having a structure in which a signal attenuator is connected to the rear of the signal amplifier, and the signal amplifier of the previous stage amplifies the signal so as to have a predetermined gain. The processed signal is attenuated by the signal attenuator in the subsequent stage so as to cancel the gain.
As a result, even when the signal is transmitted through the signal path circuit, the generation of noise and transmission loss is suppressed for the input signal, and an output signal having a substantially unchanged signal level is output. Can be output. Therefore, it is possible to realize a booster including a signal path circuit having a good CN ratio and excellent transmission characteristics.

Here, by applying an attenuator (ATT) for attenuating the gain of the signal as the signal attenuator, the signal attenuator (ATT) is originally provided in the booster in order to realize the signal amplifying function. The signal path circuit described above can be realized with a simple configuration in which one or a plurality of attenuators are connected in series. Particularly when the signal amplification circuit and the signal path circuit are formed on the same substrate, the signal output from the signal amplification unit and the signal output from the signal amplification unit via the signal attenuator (attenuator). Is provided with a selector switch for selectively switching and outputting the signal, and when the signal from the signal amplifier is selected by the selector switch, a signal amplifier circuit that outputs a signal having a predetermined gain is configured. Since a signal path circuit that outputs a signal having the same signal level as the input signal when the signal from the amplifier is selected is configured, the signal attenuator (attenuator) is added in addition to the signal amplifier originally provided in the booster. ) And a changeover switch, a booster having a signal amplification function and a signal path function can be realized with a simple configuration. Here, in the changeover switch, by providing a contact that interrupts the signal path, it is possible to easily realize a booster having a signal cut function in addition to the signal amplification function and the signal path function.

Further, according to the booster having such a circuit configuration, even when the signal amplifier circuit and the signal path circuit are formed on the same substrate, noise (amplifier noise) generated on the signal amplifier circuit side is generated. Since it does not mix into the signal path circuit side, expensive circuit components such as the high-frequency relays described above are inserted in the signal path to electrically separate the signal paths of both the signal amplifier circuit and the signal path circuit. It is not necessary to perform (isolation), simplifying the circuit configuration of the booster and improving the transmission characteristics.
Product costs can be reduced. Therefore, by applying such a booster to the common listening transmission line of the CATV system, various noises generated in each dwelling unit or in the middle of the common listening transmission line are added, amplified and transmitted in the upstream line. Since combined noise is suppressed, it is possible to significantly improve the transmission characteristics (CN ratio) in the network.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. First, a signal path circuit applied to the booster according to the present invention will be described. Figure 1
2 is a schematic configuration diagram showing an embodiment of a signal path circuit applied to a booster according to the present invention, and FIG. 2 is a signal waveform diagram showing transmission characteristics in the signal path circuit according to the present embodiment.

The signal path circuit according to this embodiment is roughly
As shown in FIG. 1, a signal amplification unit APa including amplifiers AMP1 and AMP2 and a gain controller GC between an input terminal IN and an output terminal OUT, and the signal amplification unit AP.
The signal attenuator ATa provided in the subsequent stage of a and including the attenuators ATT in a plurality of stages, and the bandpass filter BPF provided in the previous stage of the signal amplification unit APa and the subsequent stage of the signal attenuator ATa are connected. Have

The signal amplification section APa is a signal which is input from the input terminal IN and band-limited by the input side band-pass filter BPF so that only signal components in a predetermined frequency band (for example, 10 to 55 MHz) pass. On the other hand, the amplifiers AMP1 and AMP2 and the gain controller GC perform amplification processing at a signal amplification factor of a predetermined gain (for example, 30 dB). The signal attenuator ATa has a plurality of stages (here, three stages) of attenuators ATT having a signal attenuation rate of a predetermined gain (for example, 10 dB) with respect to the signal amplified by the signal amplifier Apa. Attenuation processing is performed. The signal attenuated by the signal attenuator ATa is again output by the output side bandpass filter BPF.
The signal is output from the output terminal OUT as an output signal after being band-limited so that only signal components in a predetermined frequency band (for example, 10 to 55 MHz) pass.

In the signal path circuit having such a configuration, the transmission characteristics in the signal amplification section APa are shown in FIG.
As shown in (a), of the input signals, for example, CAT
Approximately 10-55 MH applied to the uplink of V system
Only the signal component in the z frequency band is amplified with a signal amplification factor of a gain of 30 dB and output to the contact Na. on the other hand,
As shown in FIG. 2B, the transmission characteristic of the signal attenuator ATa is three stages with a gain of 10 dB set in each attenuator ATT for the input signal (signal of the contact Na) to the signal attenuator ATa. The signal is attenuated with the superimposed signal attenuation factor of −30 dB, and output to the output terminal OUT.

Therefore, the transmission characteristic of the entire signal path circuit according to this embodiment is, as shown in FIG. 2C, an input that is input from the input terminal IN and is composed of signal components in the frequency band of approximately 10 to 55 MHz. The signal is amplified by the signal amplification unit APa at a signal amplification rate of 30 dB and then attenuated at a signal attenuation rate of 30 dB by the signal attenuator ATa via the contact Na, and output terminal OUT.
Output from the output terminal OUT, since the gain component applied to the signal path circuit is canceled out, the output signal having the original signal level of the signal input to the input terminal IN is substantially output.
Will be output from. As a result, it is possible to realize a signal path circuit in which noise and transmission loss are favorably suppressed with respect to an input signal.

The frequency band of the signal processed by the signal path circuit shown in this embodiment (10 to 55 MHz)
The gain and the gain (30 dB) are merely examples for convenience of description, and the present invention is not limited thereto.
Therefore, when the CATV system or the like is applied to the co-listening transmission line, it may be appropriately set according to the system specifications and the like. Further, the number of amplifiers in the signal amplifier APa and the number of attenuators in the signal attenuator ATa are not limited to this, and may be set appropriately.

Next, a schematic structure of the booster having the above-mentioned signal path circuit will be described. FIG. 3 is a schematic configuration diagram showing an embodiment of the booster including the signal path circuit described above, and FIG. 4 is a signal waveform diagram showing the transmission characteristic of the booster according to the present embodiment.

The booster according to this embodiment is schematically shown in FIG.
As shown in FIG. 5, a configuration in which a downstream side amplification function unit APd and an upstream side amplification function unit APu are connected in parallel via the demultiplexer mixer Ds between the input terminal IN and the output terminal OUT. In particular, the upstream side amplification function unit APu includes an input side band pass filter BPF and an amplifier AM.
A signal amplification unit APb (corresponding to the signal amplification unit APa of the signal path circuit shown in FIG. 1) including P11, AMP12, and a gain controller GC, and three contact points Nx provided on the output side of the signal amplification unit APb, respectively. Changeover switches SWx and SWy having Ny and Nz, and a changeover switch S
A signal attenuator ATb (corresponding to the signal attenuator ATa of the signal path circuit shown in FIG. 1), which is connected between specific contacts Nx of Wx and SWy, and includes three-stage attenuator ATT;
The configuration includes a signal line La connected between specific contacts Ny of the changeover switches SWx and SWy, and an output-side bandpass filter BPF.

Here, the amplifiers AMP11 and AMP12 and the gain controller GC which constitute the signal amplification section APb.
The gain realized by is originally set to correspond to the gain that the booster has as a signal amplification function. For convenience of description, the amplifiers AMP11 and AM that configure the signal amplification unit APb are similar to the signal path circuit described above.
The gain (signal amplification rate) set by P12 and the gain controller GC is set to 30 dB, and the gain (signal attenuation rate) set to each of the three-stage attenuators ATT constituting the signal attenuator ATb is set to 10 dB. Further, the frequency band of the signal band-limited by the bandpass filter BPF on the input side and the output side is set to 10 to 55 MHz.

In the booster having such a structure, the changeover switches SWx and SWy are changed over to the Nx contact, and the signal amplifying section APb and the signal line La are provided between the input terminal (upstream input) and the output terminal (upstream output). And a band-pass filter BPF on the input / output side are connected to each other to form a signal path, so that an input signal (up to about 10) on the upstream side input to the amplification function unit APu via the demultiplexing mixer Ds.
Signal component having a frequency band of ˜55 MHz) is shown in FIG.
As shown in (a), a signal amplification path (signal amplification circuit) that is amplified by the gain 30 dB set in the signal amplification unit APb and output as an output signal is set.

Further, the changeover switches SWx and SWy are switched to Ny contacts, and a signal in which the signal amplifying section APb, the signal attenuating section ATb, and the input / output side bandpass filter BPF are connected between the input terminal and the output terminal. By forming the path, as in the case shown in FIG. 2C, the gain (3
0 dB) is attenuated by the signal attenuator ATb (-3
(10 dB), the signal path path is output as an output signal having substantially the signal level originally possessed by the input signal (without insertion loss) as a result of the cancellation (see FIG. 4B). Signal path circuit) is set.

Further, changeover switches SWx, SWy
Is switched to the Nz contact to disconnect the signal path between the input terminal and the output terminal, thereby cutting off the output of the signal based on the input signal as shown in FIG. A signal cut path (signal cut circuit) through which a signal having a level is output is set. In this embodiment, since the signal path is electrically cut off by switching the contacts of the changeover switches SWx, SWy, the changeover switches SWx, Sx
Wy isolation (ie switch characteristics)
Although the output signal slightly fluctuates depending on the above, it does not greatly affect the transmission characteristics in the actual product.

On the other hand, the amplification function section APd on the downlink side has a signal path in which the amplifier AMP21 is connected between the input terminal (downstream input) and the output terminal (downstream output), so that the demultiplexing mixing is performed. The input signal on the downlink side (signal component having a frequency band of approximately 70 to 770 MHz) input via the device Ds is amplified by the amplifier AMP21 so as to have a predetermined gain and output as an output signal.

That is, in the booster according to this embodiment, by operating the changeover switches SWx and SWy, one of the signal amplification function, the signal path function, and the signal cut function is selected as the signal path on the upstream side. In the design and construction of the co-listening transmission line of the CATV system, any function (signal amplification function, signal path function or signal cutting function) required in the co-listening transmission line can be set. Can be easily realized.

Here, in the above-described embodiment, the configuration is shown in which the signal attenuator composed of the attenuator is connected to the subsequent stage of the signal amplifier in the setting state of the signal path circuit, but it is similar to the booster according to the present invention. According to the technical idea, a configuration is conceivable in which an attenuator is connected before the signal amplification section. However, in such a configuration, since the signal level is attenuated by the attenuator and then the signal is input to the signal amplification unit, the gain in the output signal is canceled, but the amplifier noise generated in the signal amplification unit is canceled. However, there is a problem in that it is not possible to suppress the above and is directly affected by it.

On the other hand, in the booster according to the present invention, in the setting state of the signal path circuit, the gain given in the signal amplifying section is canceled by the signal attenuating section, and the amplifier noise generated in the signal amplifying section. Since both of the signal level (C) of the carrier wave and the noise (N), which are parameters of the CN ratio, are reduced by suppressing both of them at the same time, the deterioration of the CN ratio is suppressed while suppressing the insertion loss. It is possible to make a great improvement, and it is possible to realize a network (co-listening transmission path) having good transmission characteristics.

Further, according to the booster having such a circuit configuration, even when the signal amplifying circuit and the signal path circuit are formed on the same substrate, the noise (amplifier noise) generated in the signal amplifying section is a signal. Since it does not affect the path circuit side, it does not require an expensive and complicated circuit configuration for isolation, and it has a simple and inexpensive circuit configuration with an attenuator and changeover switch with a simple configuration, and good transmission. A booster having characteristics can be realized.

In the booster according to the present embodiment, the gain (signal amplification rate) in the signal amplification section APa is set to 30 dB, and the gain (signal attenuation rate) in the signal attenuation section ATb is set to 10 dB to cancel this gain. Although the configuration in which the attenuator ATT having a) is fixedly connected in three stages is shown, the present invention is not limited to this, and the signal attenuation rate in the signal attenuating section ATb is changed to the signal amplification rate in the signal amplifying section APa. It may be configured appropriately so that it can be adjusted correspondingly. For example, a switch for switching the connection relationship between the attenuators ATT is provided between each attenuator ATT (signal attenuation rate 30 dB) that constitutes the signal attenuator ATb, and the number of attenuator ATT connections can be arbitrarily changed by appropriately setting the switch. Let the signal attenuator A
The transmission characteristic (signal attenuation rate) of Tb may be changed. Further, as another configuration example, the signal attenuator ATb
Each attenuator ATT constituting the above may be configured to be attachable / detachable to / from the circuit board of the booster, and may be replaced with another attenuator having an arbitrary gain (signal attenuation rate) as needed. The attenuator ATb may be composed of a single attenuator.

[0036]

According to the booster of the present invention, a signal path circuit having a configuration in which a signal attenuator is connected to a stage subsequent to the signal amplifier is provided, and a predetermined gain is provided by the signal amplifier in the preceding stage. Since the signal that has been subjected to the amplification processing is attenuated by the signal attenuator in the subsequent stage so as to cancel the gain, even if the signal is transmitted through the signal path circuit, As a result, the generation of noise and transmission loss is suppressed, and it is possible to output an output signal having a substantially same signal level. Therefore, it is possible to realize a booster including a signal path circuit having a good CN ratio and excellent transmission characteristics.

Here, by applying an attenuator (ATT) for attenuating the gain of the signal as the signal attenuator, the signal attenuator (ATT) is provided after the signal amplifier originally provided in the booster to realize the signal amplifying function. The signal path circuit described above can be realized with a simple configuration in which one or a plurality of attenuators are connected in series. Particularly when the signal amplification circuit and the signal path circuit are formed on the same substrate, the signal output from the signal amplification unit and the signal output from the signal amplification unit via the signal attenuator (attenuator). Is provided with a selector switch for selectively switching and outputting the signal, and when the signal from the signal amplifier is selected by the selector switch, a signal amplifier circuit that outputs a signal having a predetermined gain is configured. Since a signal path circuit that outputs a signal having the same signal level as the input signal when the signal from the amplifier is selected is configured, the signal attenuator (attenuator) is added in addition to the signal amplifier originally provided in the booster. ) And a changeover switch, a booster having at least a signal amplification function and a signal path function can be realized with a simple configuration.

Further, according to the booster having such a circuit configuration, noise (amplifier noise) generated on the signal amplification circuit side does not mix into the signal path circuit side, so that the signal amplification circuit and the signal path circuit are not affected. Since it is not necessary to electrically separate the two signal paths (to provide isolation), the transmission characteristics can be improved and the product cost can be reduced while simplifying the circuit configuration of the booster. Therefore, by applying such a booster to the common listening transmission line of the CATV system, various noises generated in each dwelling unit or in the middle of the common listening transmission line are added, amplified and transmitted in the upstream line. Since combined noise is suppressed, it is possible to significantly improve the transmission characteristics (CN ratio) in the network.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of a signal path circuit applied to a booster according to the present invention.

FIG. 2 is a signal waveform diagram showing transmission characteristics in the signal path circuit according to the present embodiment.

FIG. 3 is a schematic configuration diagram showing an embodiment of a booster including the signal path circuit according to the present embodiment.

FIG. 4 is a signal waveform diagram showing transmission characteristics in the booster according to the present embodiment.

FIG. 5 is a diagram showing setting states of signal frequencies in an uplink and a downlink applied to a bidirectional CATV system.

FIG. 6 is a schematic circuit configuration of a bidirectional booster in the related art.

FIG. 7 is a signal waveform diagram showing a transmission characteristic of a booster in a conventional technique.

[Explanation of symbols]

APu Uplink side amplification function APd Downlink side amplification function unit APa, APb signal amplifier ATa, ATb signal attenuator SWx, SWy changeover switch

Claims (6)

[Claims] 1. A booster having at least a signal amplification function of amplifying an input signal so as to have a predetermined gain, and a signal path function of passing the input signal as it is, A signal including a signal amplifier that amplifies the generated signal so as to have a predetermined gain, and a signal attenuator that is provided at a subsequent stage of the signal amplifier and that attenuates the gain of the signal amplified by the signal amplifier. A booster characterized by having a pass circuit. 2. The signal path circuit is set so that the gain applied to the signal in the signal amplifying section is canceled by the attenuation processing of the gain in the signal attenuating section. The booster according to Item 1. 3. The booster according to claim 1, wherein the signal attenuator has a configuration in which a plurality of attenuators are connected in series. 4. The booster comprises a changeover switch for selectively changing and outputting at least the output signal of the signal amplifying section and the output signal of the signal attenuating section. Booster described in any of. 5. The booster has a signal cut function for interrupting output of a signal based on the input signal by switching the changeover switch. Booster described in either. 6. The booster according to any one of claims 1 to 5, wherein the booster is installed in a co-listening transmission line that constitutes a cable television system.