JP5575586B2 - Video distribution transmission equipment - Google Patents

Description

  The present invention relates to a video distribution transmission apparatus capable of controlling viewing restrictions.

  In CATV, conventionally, video and audio are restricted by using a video distribution transmission device installed in a subscriber's house. In this video distribution transmission device, the TV receiver itself connected to the video distribution transmission device is turned on / off corresponding to the viewing restriction of the TV signal output itself among the TV signals transmitted from the CATV center. It is attempted not to transmit a TV signal whose viewing is restricted. In this system, an FSK (Frequency Shift Keying) transmitter is installed at the center of CATV, and the control signal for each video distribution transmission device having individual identification information is set to a frequency slightly below the broadcast band. It is mixed with other TV broadcast signals at 70-76 MHz. The video distribution transmission device extracts the control signal to which the identification information of the local station is added from the control signal mixed with the TV signal transmitted from the center, and transmits the TV signal according to the control signal. Control to turn the output ON / OFF. As a result, it is possible to perform viewing restriction control for subscribers whose viewing is restricted.

FIG. 5 shows an example of a circuit configuration of a conventional video distribution transmission device capable of performing such viewing restrictions.
In the video distribution transmission apparatus 100 shown in FIG. 5, the distribution signal distributed from the CATV center is a TV signal mixed with a control signal for viewing restriction, and is transmitted as an optical signal to each subscriber's home via the optical fiber 110. be delivered. The optical signal propagated through the optical fiber 110 drawn into the subscriber's home is input to the video distribution transmission device 100 and converted into an electrical signal by the photodiode (PD) 111. The distribution signal converted into the converted electric signal is amplified by an amplifier (AMP) 113 and subjected to level control in an automatic gain control unit (AGC) 114 so as to reach a predetermined level. In this case, the level of the distribution signal output from the PD 111 is detected by the AGC circuit 112, and the AGC circuit 112 sends a level control signal corresponding to the detected level of the distribution signal to the AGC 114. The AGC 114 controls the level of the distribution signal from the AMP 113 according to the level control signal. The TV signal set to a predetermined level by the AGC 114 is supplied to the high-pass filter (HPF) 116 and the low-pass filter (LPF) 122 via the branching unit 115, and a part of the distribution signal branched by the branching unit 115 is FSK. The signal is input to the signal receiving unit 129.

The HPF 116 extracts the TV signal in the BS / CS-IF frequency band, and the gain control unit (GC) 117 controls the level of the extracted TV signal in the BS / CS-IF system so as to be a predetermined level. Amplified by AMP118, AMP119, and AMP120 of the stage. The amplified BS / CS-IF TV signal from the AMP 120 is output after the unnecessary wave component is removed by the HPF 121. The LPF 122 extracts a TV signal in the V / UHF frequency band. The gain control unit (GC) 123 controls the level of the extracted V / UHF TV signal so that the TV signal becomes a predetermined level. It is amplified by AMP124, AMP125, and AMP126. The amplified V / UHF TV signal from the AMP 126 is output after the unnecessary wave component is removed by the LPF 127.
The BS / CS-IF TV signal output from the HPF 121 and the V / UHF TV signal output from the LPF 127 are mixed and output from the output terminal OUT128. A TV receiver is connected to the output terminal OUT128.

  The FSK signal receiving unit 129 to which the branch output from the branching unit 115 is input receives only a control signal for viewing restriction in a band lower than the band of the TV signal mixed with the TV signal, and demodulates the control signal. . The demodulated control signal is supplied to the analysis unit CPU 130, the control signal addressed to the own station to which the identification information of the own station is added is extracted by the analysis unit CPU 130, and the extracted control signal is supplied to the control unit 131. . When the control signal addressed to the own station is a control signal for turning off the viewing of the BS / CS-IF TV signal, the control unit 131 sends a control signal for increasing the attenuation to the GC 117. As a result, the BS / CS-IF TV signal is attenuated by the GC 117 and is not output from the HPF 120. When the control signal addressed to the own station is a control signal for turning off viewing of the V / UHF TV signal, the control unit 131 sends a control signal for increasing the attenuation to the GC 123. Thus, the V / UHF TV signal is attenuated by the GC 123 and is not output from the LPF 127. Furthermore, when the control signal addressed to the own station is a control signal for turning on viewing of the TV signal of the BS / CS-IF system or the V / UHF system, the control signal for increasing the attenuation amount is not sent to the GC 117 or the GC 123. BS / CS-IF and V / UHF TV signals are output as usual without being attenuated.

JP 2008-92499 A

In the conventional video distribution transmission device 100 that can restrict viewing, the TV signal in the band (V / UHF band or BS / CS-IF band) that can be extracted by the filter is controlled to be cut or passed, and the entire band is passed. Can be controlled. In this case, even if the TV signal is cut off, it is not practical from the viewpoint of cost performance to completely cut off the TV signal, and an attenuation amount of about 60 dB is given to the TV signal, so that the TV signal is cut off and compromised. I do not get. However, the frequency becomes high as in the BS / CS-IF band, and particularly when the frequency is 2600 MHz, it is blocked by the influence of stray capacitance in the circuit of the video distribution transmission device 100 and the influence of the signal being emitted from the circuit to the space. It is difficult to give a sufficient amount of attenuation to the TV signal. As described above, when a TV signal that blocks a sufficient amount of attenuation is not provided, a booster is provided after the video distribution transmission device 100, and the TV signal amplified by the booster is input to the TV receiver. There is a problem that even a TV signal that is controlled to be cut off by the distribution transmission device 100 may be viewable.
Further, in the GC 117 and GC 123 of the video distribution transmission device 100, a PIN diode is used to attenuate the TV signal. That is, the TV signal is attenuated by the PIN diode by the control signal for turning off viewing. However, since a sufficient amount of attenuation cannot be obtained with a PIN diode, the power supply of the AMP 118 to AMP 120 and the AMP 124 to AMP 126 is turned off to stop the operation, or a relay contact that is opened and closed is inserted into the TV signal transmission path. It was necessary to earn attenuation by using the means together. Furthermore, when the attenuation amount is controlled for each band, a circuit for attenuating each band is required, which causes a problem that the circuit becomes complicated.
SUMMARY OF THE INVENTION An object of the present invention is to provide a video distribution transmission device that can be viewed and restricted with a simple circuit.

The transmission device for video distribution of the present invention extracts a control signal addressed to the own station from branching means for partially branching an input distribution signal, and the distribution signal branched by the branching means, and the extracted control signal is In the case of a control signal that turns off viewing in a predetermined frequency band, a first level control signal that periodically repeats the first level and the second level is output, and the extracted control signal is a control signal that turns on viewing A control means for outputting a second level control signal at a constant level, an extraction means for extracting a viewing signal in the predetermined frequency band from the distribution signal via the branching means, and an extraction means extracted by the extraction means Level adjustment means capable of adjusting the level of the viewing signal in the predetermined frequency band by a level control signal from the control means, the level adjustment means when receiving the first level control signal Viewing the signal of a constant frequency bands periodically by the level variation so that the level fluctuation difference of 10dB~20dB in a cycle of the first level control signal and outputs the predetermined when subjected to the second-level control signal The most important feature is that the viewing signal in the frequency band is output as a level corresponding to the second level control signal.

According to the present invention, in the case of a control signal for turning off viewing, the level of the viewing signal is periodically 10 dB to 20 dB in the period of the first level control signal that periodically repeats the first level and the second level. By changing the level so as to obtain a fluctuation difference and outputting it, it becomes impossible to view on the TV receiver. This is because the TV receiver incorporates an AGC circuit for absorbing level fluctuations, and this AGC circuit has a time constant that follows slow level fluctuations . This is because it is not possible to follow the level fluctuation of the viewing signal whose level has been changed so as to have a level fluctuation difference of 10 dB to 20 dB periodically.

It is a block circuit diagram which shows the structure of the transmission apparatus for video distribution concerning the Example of this invention. It is a circuit diagram which shows the structure of the control part and level adjustment part of the transmission apparatus for video distribution concerning this invention. It is a chart which shows the control operation of the control part and level adjustment part of the transmission apparatus for video distribution concerning this invention. It is a figure which shows the frequency characteristic of the attenuation amount of the level control of the transmission apparatus for video distribution concerning this invention. It is a block circuit diagram which shows the structure of the transmission apparatus for conventional video distribution.

FIG. 1 is a block circuit diagram showing a configuration of a video distribution transmission device 1 according to an embodiment of the present invention.
In the video distribution transmission apparatus 1 according to the present invention shown in FIG. 1, the distribution signal distributed from the CATV center is a TV signal mixed with a control signal for viewing restriction. It is distributed as an optical signal. The optical signal propagated through the optical fiber 10 drawn into the subscriber's home is input to the video distribution transmission device 1 and converted into an electrical signal by the photodiode (PD) 11. The distribution signal converted into the electric signal converted by the PD 11 is amplified by the amplifier (AMP) 13 and level-controlled by the automatic gain control unit (AGC) 14 so as to reach a predetermined level. In this case, the level of the distribution signal output from the PD 11 is detected by the AGC circuit 12, and the AGC circuit 12 sends a level control signal corresponding to the detected level of the distribution signal to the AGC 14. The AGC 14 controls the level of the distribution signal from the AMP 13 according to the level control signal. The TV signal set to a predetermined level by the AGC 14 is supplied to the high-pass filter (HPF) 19 and the low-pass filter (LPF) 22 via the branching unit 15, and a part of the distribution signal branched by the branching unit 15 is FSK. The signal is input to the signal receiver 16.

The HPF 19 extracts a TV signal in the BS / CS-IF frequency band. The level of the extracted BS / CS-IF TV signal is controlled by the level adjusting unit 20, and unnecessary wave components are removed by the HPF 21. Is output. The LPF 22 extracts a TV signal in the V / UHF frequency band, and the level of the extracted V / UHF TV signal is controlled by the level adjusting unit 23, and unnecessary wave components are removed by the LPF 127 and output. The The BS / CS-IF TV signal output from the HPF 21 and the V / UHF TV signal output from the LPF 24 are mixed and amplified by amplifiers AMP25, AMP26, and AMP27 that are cascaded in three stages. . A TV signal obtained by mixing the amplified BS / CS-IF system and V / UHF system from the AMP 27 is output from an output terminal (OUT) 28. A TV receiver is connected to OUT28.
The HPF 19, the level adjustment unit 20, and the HPF 21 constitute a first level adjustment system for controlling the level of the BS / CS-IF type TV signal, and the LPF 22, the level adjustment unit 23, and the LPF 24 constitute a V / UHF type TV signal. A second level adjustment system is configured to control the level of.

  The FSK signal receiving unit 16 to which the branch output from the branching unit 15 is input receives only a control signal for viewing restriction in a band lower than the band of the TV signal mixed with the TV signal, and demodulates the control signal. . The demodulated control signal is supplied to the analysis unit CPU 17, the control signal addressed to the own station to which the identification information of the own station is added is extracted by the analysis unit CPU 17, and the extracted control signal is supplied to the control unit 18. . When the control signal addressed to the own station is a control signal for turning off viewing of the TV signal of the BS / CS-IF system, the control unit 18 periodically sets the first level and the second level to the level adjustment unit 20. A first level control signal having a repeated rectangular wave is sent. As a result, the level adjusting unit 20 modulates the amplitude of the BS / CS-IF TV signal by the first level control signal (rectangular wave) and periodically outputs the level-changed signal in the period of the first level control signal. Become so. Further, when the control signal addressed to the own station is a control signal for turning on viewing of the BS / CS-IF type TV signal, the control unit 18 controls the second level control in which the level adjustment unit 20 is set to a predetermined constant level. Send a signal. As a result, the level adjusting unit 20 outputs a BS / CS-IF-based TV signal that is level-controlled according to the level of the second level control signal.

  Further, when the control signal addressed to the own station is a control signal for turning off viewing of the TV signal of the V / UHF TV signal, the control unit 18 sets the first level and the second level to the level adjustment unit 23. A first level control signal that is a periodically repeating rectangular wave is sent. As a result, the V / UHF TV signal is amplitude-modulated by the first level control signal (rectangular wave) in the level adjusting unit 23, and the level is periodically changed in the cycle of the first level control signal and output. become. When the control signal addressed to the own station is a control signal for turning on viewing of a V / UHF TV signal, the control unit 18 sends a second level control signal set to a predetermined constant level to the level adjustment unit 20. send. As a result, the V / UHF TV signal is level-controlled in the level adjusting unit 20 according to the level of the second level control signal and is output.

The TV receiver connected to OUT28 has a built-in AGC circuit. This is because the reception level varies depending on the electric field in the area where the TV receiver is installed, the influence of reflectors on the spatial transmission path, such as flutter obstruction due to airplanes and sea level fluctuations, seasonal fading, etc. This is because it is necessary to absorb level fluctuations caused by obstacles. These level fluctuations have a time constant longer than several tens of Hz, and the TV receiver follows this time constant. However, it has been found that when the level changes in a cycle shorter than this time constant, the TV receiver cannot follow the level fluctuation, and the image is disturbed and the image cannot be viewed. In particular, an error occurs in digital broadcasting, and the image cannot be reproduced. It was confirmed that the image was disturbed when the frequency of the level change at this time was several hundred Hz or more and the level fluctuation difference was about 10 to 20 dB. In the video distribution transmission device 1 according to the present invention, by using this phenomenon, the level of the output from the video distribution transmission device 1 is varied at a frequency of several hundreds of Hz or more so that TV viewing cannot be performed. Yes. That is, the oscillation frequency of the oscillation signal used as the first level control signal is several hundred Hz or more, and preferably about 1 kHz to 2 kHz.
Furthermore, when the FSK signal receiving unit 16 cannot receive the FSK control signal, the control unit 18 may reduce power consumption by performing control to turn off the power of the AMP25 to AMP27.

  Next, the analysis unit CPU 17 controls the viewing of the BS / CS-IF TV signal and the control signal (BS / CS-IF) for controlling the viewing of the V / UHF TV signal. V / UHF) are output to the control unit 18. The control unit 18 receives a control signal (BS / CS-IF) and controls the level of the BS / CS-IF level adjustment unit 20. The control unit 18-1 also controls the control signal (V / UHF). Is input, and a second control unit 18-2 that performs level control of the level adjustment unit 23 of the V / UHF system is provided. The circuit configurations of the first control unit 18-1 and the second control unit 18-2 are the same. The level adjustment unit 20 and the level adjustment unit 23 have the same circuit configuration. FIG. 2 shows a circuit diagram of the first control unit 18-1 and the level adjustment unit 20 in FIG. Further, the control operation of the level adjusting unit 20 is shown in the chart of FIG.

  The circuits of the first control unit 18-1 and the level adjustment unit 20 shown in FIG. 2 will be described with reference to the chart shown in FIG. In the first control unit 18-1, the control signal (BS / CS-IF) among the control signals of the own station detected by the analysis unit CPU 17 is input to the base of the switching transistor TR1 through the resistor R2. . The transistor TR1 is turned on / off according to the level of the control signal (BS / CS-IF). The emitter of the transistor TR1 is grounded, and the collector is connected to the input of the inverter INV that constitutes the oscillation circuit section OSC. Thus, the input side of the oscillation circuit section OSC is opened or grounded according to the on / off state of the transistor TR1, and it is controlled whether the oscillation circuit OSC oscillates or is stopped. The oscillation circuit unit OSC includes an inverter INV, a negative feedback resistor R3 connected between the input and output of the inverter INV, and a capacitor C4 connected between the input of the inverter INV and the ground. The resistor R3 and the capacitor The oscillation frequency is determined by the time constant with C4. The output of the oscillation circuit OSC is input to the base of the switching transistor TR2 via the resistor R4. The emitter of the transistor TR2 is grounded, the collector is an output to the level adjusting unit 20, and a bypass capacitor C5 is connected between the collector and the ground to reduce the impedance of the collector in terms of high frequency. The transistor TR2 is turned on / off according to the output level of the oscillation circuit OSC.

  The level adjusting unit 20 receives a BS / CS-IF TV signal from the HPF 19 at an input terminal (RF IN). Further, a terminal to which the power supply Vcc is supplied and a terminal to which the control voltage Vs is supplied are provided. The BS / CS-IF system TV signal input to the input terminal is supplied to two first PIN diodes (PIN1) and second PIN diodes (PIN2) connected in series via capacitors C1 and C2 connected in series. It is input to two third PIN diodes (PIN3) and a fourth PIN diode (PIN4) connected in series via a capacitor C1. For example, a power supply Vcc of about 12 V is supplied to the connection point between the capacitor C1 and the capacitor C2 via the resistor R1, and the control voltage Vs is supplied to the connection point between the capacitor C2 and the anode of the PIN1 via the choke coil CH1. . The control voltage Vs can be varied, for example, can be varied between about 2V to 12V. A capacitor C6 is connected between the connection point between the cathode of PIN3 and the anode of PIN4 and the ground, and the impedance at the connection point is reduced in terms of high frequency. Further, the cathode of PIN2 and the cathode of PIN4 are connected, and the output is output to the output terminal (RF OUT) via the capacitor C3. An output from the output terminal (RF OUT) is input to the AMP 25. A connection point between the cathode of PIN2 and the cathode of PIN4 is connected to the collector of the transistor TR2, which is the output of the first controller 18-1, via a resistor R5.

  When the control signal (BS / CS-IF) input to the first control unit 18-1 is at a high level (High), the control signal is used to turn on viewing of the BS / CS-IF TV signal. The transistor TR1 is turned on and the input side of the oscillation circuit unit OSC is grounded. Thereby, the oscillation of the oscillation circuit OSC is stopped, and the output of the oscillation circuit OSC becomes high level (High). The output of the oscillation circuit section OSC is input to the base of the transistor TR2 via the resistor R4, and the transistor TR2 is turned on. As a result, the cathode of PIN2 and the cathode of PIN4 are grounded via resistor R5 and the collector-emitter of transistor TR2. Therefore, a current is supplied from the power source Vcc to the PIN3 and PIN4 via the resistor R1, and the PIN3 and PIN4 become low in impedance. Further, a current is supplied from the control voltage Vs to the PIN1 and PIN2 via the choke coil CH1 to be conducted, and the impedances of the PIN1 and PIN2 are lowered. As a result, the BS / CS-IF TV signal input to the input terminal (RF IN) passes through PIN 1 to PIN 4 having a low impedance and is output from the output terminal (RF OUT). However, since the impedances of PIN1 and PIN2 change when the control voltage Vs is varied, the BS / CS-IF TV signal output from the output terminal (RF OUT) according to the magnitude of the control voltage Vs. The output level can be controlled. That is, when the control voltage Vs is maximized (for example, approximately 12 V), the output level of the BS / CS-IF system TV signal output from the output terminal (RF OUT) is maximized, and the control voltage Vs is minimized (for example, approximately 2V), the output level of the BS / CS-IF TV signal output from the output terminal (RF OUT) is minimized.

  When the control signal (BS / CS-IF) input to the first control unit 18-1 is at a low level (Low), the control signal is used to turn off viewing of the BS / CS-IF TV signal. Thus, the transistor TR1 is turned off and the input side of the oscillation circuit unit OSC is in an open state. As a result, the oscillation circuit OSC oscillates, and a rectangular wave having a predetermined frequency in which the high level and the low level are periodically repeated is output from the oscillation circuit OSC. The oscillation output of the oscillation circuit section OSC is input to the base of the transistor TR2 via the resistor R4, and the transistor TR2 is repeatedly turned on / off periodically. During the period in which the transistor TR2 is off, the cathode of PIN2 and the cathode of PIN4 are open in a direct current state so that no current flows, PIN3 and PIN4 become non-conducting, impedance increases, and PIN1 and PIN2 also becomes non-conductive and impedance increases. Then, the BS / CS-IF TV signal input to the input terminal (RF IN) is greatly attenuated by the PIN1 to PIN4 whose impedance is increased, and is output from the output terminal (RF OUT). Further, during the period when the transistor TR2 is on, the cathode of PIN2 and the cathode of PIN4 are grounded via the transistor TR2 as described above, and PIN3 and PIN4 are conducted to reduce the impedance, and PIN1 and PIN2 Is also conducted and the impedance is lowered. As a result, the BS / CS-IF type TV signal input to the input terminal (RF IN) passes through the PIN 1 to PIN 4 whose impedance is low without being attenuated and is output from the output terminal (RF OUT). become.

In this case, since the transistor TR2 is periodically turned on / off, the PIN1 to PIN4 are periodically turned on / off. As a result, the BS / CS-IF TV signal input to the input terminal (RF IN) is output from the output terminal (RF OUT) without being attenuated when the PIN 1 to PIN 4 are conducted, but the PIN 1 to PIN 1 When PIN4 is non-conductive, it is greatly attenuated and output from the output terminal (RF OUT). That is, the output level of the BS / CS-IF TV signal input to the input terminal (RF IN) is periodically changed in accordance with the oscillation output of the oscillation circuit unit OSC and output from the output terminal (RF OUT). Become so. In this case, since the impedances of PIN1 and PIN2 change when the control voltage Vs is varied, the BS / CS-IF TV signal output from the output terminal (RF OUT) according to the magnitude of the control voltage Vs. Level fluctuation difference is determined.
The circuit diagram of the second control unit 18-2 that receives the control signal (V / UHF) and controls the level of the level adjustment unit 23 of the V / UHF system and the level adjustment unit 23 is the circuit shown in FIG. The same operation as that shown in FIG. 3 is performed. The oscillation frequency of the oscillation circuit unit OSC is several hundreds Hz or more, preferably 1 kHz to 2 kHz.

FIG. 4 shows the frequency characteristics of the attenuation amounts in the first control unit 18-1 and the level adjustment unit 20 which are the circuit diagram shown in FIG.
In FIG. 4, the frequency characteristic of the attenuation indicated by the two-dot chain line is a characteristic when the control voltage Vs is varied to the maximum voltage (for example, about 12 V). The frequency characteristic of the attenuation indicated by the one-dot chain line is This is a characteristic when the control voltage Vs is changed to a minimum voltage (for example, about 2 V). By varying the control voltage Vs, an arbitrary attenuation amount between the alternate long and short dash line is set. be able to. The frequency characteristic of the attenuation amount indicated by the solid line is the frequency characteristic of the attenuation amount when the transistor TR2 is turned off and the cathodes of PIN2 and PIN4 are opened. Referring to FIG. 4, when the control voltage Vs is set to the maximum voltage (for example, about 12V), the attenuation amount is about 0 dB in the frequency band of about 90 MHz to about 2600 MHz, and slightly attenuates when the frequency becomes high. . Further, when the control voltage Vs is set to the minimum voltage (for example, about 2 V), the attenuation amount is about 10 dB at about 90 MHz, and the attenuation amount gradually increases as the frequency increases, and about 12 dB at about 2600 MHz. Attenuation amount. Further, when the transistor TR2 is turned off and the cathodes of PIN2 and PIN4 are in an open state, the attenuation is about 33 dB at about 90 MHz, and the attenuation gradually decreases as the frequency increases, and about 19 dB at about 2600 MHz. Attenuation amount.

Note that the second control unit 18-2 that performs level control of the V / UHF level adjusting unit 23 when the control signal (V / UHF) is input and the frequency characteristics of the attenuation amount of the level adjusting unit 23 are also shown in FIG. This is the same as the frequency characteristic of the attenuation shown in FIG.
As described above, the level adjustment unit 20 (23) controlled by the oscillation output of the oscillating oscillation circuit OSC can provide the TV signal when the control voltage Vs is set to the maximum voltage (for example, about 12 V). The level fluctuation difference is the difference between the minimum attenuation indicated by the alternate long and short dash line and the attenuation in the open state, and is at least about 18 dB or more. Further, when the control voltage Vs is set to the minimum voltage (for example, about 2 V), the level variation difference given to the TV signal is the same as described above and is at least about 8 dB or more. As a result, even when viewing the TV signal via the level adjustment unit 20 (23) controlled by the oscillation output of the oscillating oscillation circuit OSC, the image is distorted or the image cannot be reproduced and cannot be viewed. It becomes like this. That is, the video distribution transmission device according to the present invention can restrict viewing regardless of whether it is an analog broadcast or a digital broadcast.
Further, by varying the control voltage Vs, it is possible to set an arbitrary attenuation amount between about 0 dB and about 10 dB between the one-dot chain line and the two-dot chain line.

In the video distribution transmission apparatus according to the present invention described above, the conventional viewing restriction by ON / OFF control requires isolation of 60 dB or more, but gives a TV signal a level fluctuation of about 10 to 20 dB. This makes it possible to limit viewing, and the circuit becomes simple and inexpensive. When viewing is turned on (the oscillation circuit OSC stops oscillating), the level adjustment unit 20 (23) can adjust the output level by varying the control voltage Vs. Thus, in the video delivery transmission apparatus according to the present invention, the level adjustment unit 20 (23) for adjusting the output level is also used as a viewing restriction circuit.
Further, in the video delivery transmission apparatus according to the present invention, the receiver, which was a drawback of the conventional ON / OFF control method, is not viewable even if an amplifier is used.
Furthermore, if the period for changing the gain is slowed or a plurality of periods are combined, noise will appear in the video and audio, but the content can be discriminated. This can be used to create an appealing effect for viewers and invite them to purchase.
Furthermore, when the FSK signal receiving unit 16 cannot receive the FSK control signal, the control unit 18 can perform the control to turn off the power of the AMP25 to AMP27, thereby surely limiting the viewing and reducing the power consumption. Can do.
In the above description, the oscillation circuit OSC is configured by an inverter, but is not limited thereto, and may be an oscillation circuit using an OP amplifier or an oscillation circuit using an active element such as a transistor.

DESCRIPTION OF SYMBOLS 1 Transmission equipment for video distribution, 10 Optical fiber, 11 Photodiode, 12 AGC circuit, 13 AMP, 14 AGC, 15 Branch, 16 FSK signal receiving part, 17 Analysis part CPU, 18 Control part, 18-1 1st control Unit, 19 HPF, 20 level adjustment unit, 21 HPF, 22 LPF, 23 level adjustment unit, 24 LPF, 25-27 AMP, 28 output terminal, 100 video distribution transmission equipment, 110 optical fiber, 111 photodiode, 112 AGC Circuit, 113 AMP, 114 AGC, 115 branching device, 116 HPF, 117 GC, 118-120 AMP, 121 HPF, 122 LPF, 123 GC, 124-126 AMP, 127 LPF, 129 FSK signal receiving unit, 130 analysis unit CPU 131 control unit

Claims (5)

Branching means for partially branching the input distribution signal;
A control signal destined for the local station is extracted from the distribution signal branched by the branching means, and the first level and the second level when the extracted control signal is a control signal for turning off viewing in a predetermined frequency band. A control means for outputting a first level control signal that periodically repeats and outputting a second level control signal that is set to a constant level when the extracted control signal is a control signal for turning on viewing;
Extracting means for extracting a viewing signal of the predetermined frequency band from the distribution signal via the branching means;
Level adjustment means capable of adjusting the level of the viewing signal in the predetermined frequency band extracted by the extraction means by a level control signal from the control means;
When the level adjusting means receives the first level control signal, the level adjustment means periodically changes the viewing signal of the predetermined frequency band to a level fluctuation difference of 10 dB to 20 dB in the period of the first level control signal. When the second level control signal is received, the viewing signal in the predetermined frequency band is output as a level corresponding to the second level control signal. Branching means for partially branching the input distribution signal;
Control means for extracting a control signal addressed to the own station from the distribution signal branched by the branch means, and outputting a level control signal corresponding to the extracted control signal;
First extraction means for extracting a viewing signal in the first frequency band from the distribution signal via the branching means, and the level of the viewing signal in the first frequency band can be adjusted by the level control signal from the control means A first level adjustment system comprising a first level adjustment means,
Second extraction means for extracting a viewing signal in the second frequency band from the distribution signal via the branching means, and the level of the viewing signal in the second frequency band can be adjusted by the level control signal from the control means A second level adjustment system comprising a second level adjustment means,
Output means for mixing and outputting the output from the first level adjustment system and the output from the second level adjustment system;
The control means applies, to the first level adjustment means, a first level control signal that periodically repeats a first level and a second level in the case of a control signal for turning off viewing of the first frequency band. The viewing signal in the first frequency band is output with a level fluctuation periodically having a level fluctuation difference of 10 dB to 20 dB in the period of the first level control signal , and the control signal is viewed in the first frequency band. A second level control signal, which is set to a constant level in the case of a control signal for turning on, is applied to the first level adjusting means, and the viewing signal in the first frequency band is set to a level corresponding to the second level control signal. Output as
The control means applies, to the second level adjustment means, a first level control signal that periodically repeats a first level and a second level in the case of a control signal for turning off viewing of the second frequency band. The viewing signal in the second frequency band is output with a level fluctuation periodically having a level fluctuation difference of 10 dB to 20 dB in the period of the first level control signal , and the control signal is viewed in the second frequency band. A second level control signal, which is set to a constant level in the case of a control signal for turning on, is applied to the second level adjusting means, and the viewing signal in the second frequency band is set to a level corresponding to the second level control signal. Video distribution transmission equipment characterized by being output as: 3. The video distribution transmission device according to claim 1, wherein the first level control signal is a rectangular wave from an oscillation circuit that oscillates at a predetermined frequency.   Amplifying means for amplifying and outputting the output from the level adjusting means is provided, and when the control means cannot receive the control signal, the control means turns off the power supply of the amplifying means. The transmission device for video distribution according to claim 1.   The output means is provided with an amplifying means for amplifying and outputting the output, and when the control means cannot receive the control signal, the control means turns off the power supply of the amplifying means. The video distribution transmission device according to claim 2.

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