JPS6284627A - Distortion monitor device - Google Patents

Abstract

PURPOSE:To accurately detect the trouble due to increase of distortion in a repeating amplifier by providing a level detector which detects the level of a detection signal passed through the 2nd filter and a means which detects an increase in distortion from a rise in the level of the detection signal and transmits a trouble detection signal to a monitor terminal. CONSTITUTION:A pilot signal which is cross-modulated by the nonlinearity of the repeating amplifier on a transmission path is extracted by the 1st filter 18, amplified by a pilot signal amplifier 19, and detected by a detector 20. The output of the detector 20 contains components of horizontal scanning frequency and frequencies which are integral multiplex of it, but the 2nd filter 9 passes one or plural components. The detection signal is amplified by a detection signal amplifier 10 and then its level is detected by the level detector 11. If the detection signal level rises abnormally, a terminal device which detects the trouble generates the trouble detection signal by a transmitting modulation circuit 28 so that the trouble is recognized by the monitor terminal, and the trouble detection signal is transmitted as an up transmit signal to the monitor terminal at a head end.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a distortion monitoring device for detecting an increase in distortion generated in a relay amplifier or the like in a transmission system such as CATV.

Conventional CATV has a tendency to become multichannel in order to provide not only simple retransmission but also a variety of services such as independent broadcasting and paid program service (Pay TV).

Accordingly, transmission lines, especially relay amplifiers, are required to have particularly high performance. Many of the major factors that reduce the reliability of such transmission systems are related to repeater amplifiers that include active elements.

One of the problems associated with repeater amplifiers is increased distortion due to excessive signal levels or amplifier failure. It is very useful to detect the occurrence of such a strain increase fault early and recognize the location of the fault, as it can shorten the time required for recovery. Such functionality is realized by a strain monitoring device that can be remotely monitored.

Conventionally, the method for detecting distortion-increasing faults is to simultaneously transmit a pilot signal of a specific frequency and detect the distortion-increasing fault indirectly by knowing the level of this pilot signal at the input or output of a relay amplifier. A method was taken to discover the Relay amplifiers equipped with such distortion fault detection units have unidirectional or bidirectional communication functions, and exchange data with monitoring terminals installed at headends, etc., to monitor the status of the relay amplifier. The most common method was to monitor

An example of such a conventional distortion monitoring device will be described below with reference to the drawings.

FIG. 4 shows an example of a CATV transmission network.

In Figure 4, 25 is the head end, 60.61.6
2 is a relay amplifier, 63 is a tap-off, 64.65 is a termination device, 68 is a terminal device, and 69 is a receiver. A downlink transmission signal such as a television signal is sent out from the head end 25, and is transmitted, for example, to a relay amplifier 60. Relay amplifier 62. The signal enters the terminal device 68 of each home via the tap-off 63, and if scrambled, is descrambled and enters the receiver 69.

In the conventional distortion monitoring device, the distortion fault detection section is placed in the relay amplifier 60, 61 of the trunk system, and in the monitoring terminal or the heel end 25. FIG. 5 shows a circuit configuration diagram of a relay amplifier in which a distortion fault detection section is installed.

In Fig. 5, -1 is an input terminal, 2 is an upper and lower signal separation filter, 3 is a down line amplifier, 4 is an up line amplifier, 6 is an upper and lower signal separation filter, 7 is an output terminal, 1 is the first filter, and 101 is the DC detector, 17 is a modulation signal generator,
16 is a modulator, 15 is a carrier wave oscillator, 14 is a multiplexer,
The relay amplifier 100 is configured as described above.

The operation of the line monitoring device configured as described above will be briefly explained below using FIG. 5.

A downlink signal consisting of a downlink video signal and a pilot signal of a specific frequency added to check the operating state of the downlink amplifier 3 enters from the input terminal 1, is separated by the upper and lower signal separation filter 2, and is sent to the downlink amplifier 3. 6 amplified by 3
The pilot signal amplified together with the downstream video signal is
It is extracted by the filter 18, detected by the DC detector 101, and the output level of the downlink amplifier 3 is measured. Therefore, if the level of this test signal appears to be abnormally high, it can be predicted that distortion has occurred. In this example, the return carrier wave obtained by the carrier wave oscillator 15 is modulated by the modulator 16 with a signal obtained by the modulation signal generator 17 whose frequency etc. can be changed according to this level value, and the signal is sent to the head as an upstream signal. By sending the signal back to the end, it is possible to monitor distortion caused by excessive input power of the relay amplifier at the head end. (Japanese Unexamined Patent Publication No. 50-33723, etc.) Problems to be Solved by the Invention However, in the above configuration, the input of the line amplifier becomes excessive in some parts of the band due to disturbances in the in-band characteristics. distortion may not be detected. This is because only the frequency of the pilot signal is monitored. Furthermore, if the line amplifier has a push-pull configuration, it may not be possible to detect an increase in distortion due to a failure of the line amplifier itself, such as a loss of balance.

Furthermore, if a fault detector for detecting level abnormalities as described above is added to every repeating amplifier, the number of fault detectors increases, resulting in an excessive cost. For this reason,
In conventional transmission systems, fault detectors are installed only in main relay amplifiers such as trunk lines, but this cannot detect failures in relay amplifiers near the end of the transmission network.In other words, failures at each home terminal cannot be detected. The problem was that the occurrence could not be accurately grasped.

In view of the above-mentioned problems, the present invention does not use indirect methods such as level monitoring, but directly detects failures at each home terminal due to increased distortion during actual video transmission service.
The present invention provides a distortion monitoring device that can accurately detect distortion.

Means for Solving the Problems In order to solve the above problems, the distortion monitoring device of the present invention includes an unmodulated biloft signal in the downlink transmission signal, and transmits a biloft signal at the end of each branched transmission path of the transmission system. In a certain terminal device, a first filter extracts the pilot signal cross-modulated due to nonlinearity of a relay amplifier on a transmission path to the terminal device, and extracts an envelope of the piezot signal that has passed through the first filter. a second filter that does not pass the DC component of the output signal of the detector; a level detector that detects the level of the detection signal that has passed through the second filter; The system is equipped with means for detecting an increase in the number of failures and transmitting a failure detection signal to a monitoring terminal.

Effect of the Invention With the above-described configuration, the present invention extracts the cross-modulation component from the transmitted television signal to the viroft signal and monitors its level at the end of the transmission network, thereby accurately detecting the total increase failure of the relay amplifier. It becomes possible to do so.

Embodiment Hereinafter, a distortion monitoring device according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a circuit configuration diagram of a terminal device in which a fault detector of a distortion monitoring device according to a first embodiment of the present invention is installed. In FIG. 1, 18 is a first filter, 19 is a pilot signal amplifier, and 20 is a detector, and these constitute a pilot signal amplification and detection section 21. Further, 9 is a second filter, 10 is a detection signal amplifier, and 11 is a level detector, and these and the pilot signal amplification/detection section 21 constitute a distortion disturbance detection section 22. Furthermore, 1 is an input terminal, 7 is a video output terminal, 27 is a reception demodulation circuit, and 2
8 is a transmission modulation circuit, 29 is an upper and lower signal separation filter, 30
31 is a keyboard, 31 is a descrambler, 38 is a control circuit, and the terminal device 5 is configured by the above.

Regarding the strain monitoring device configured as above, the following is the first part.
The operation will be explained using the diagram and FIG.

When a signal is passed through an amplifier that is generally not linear, the output contains something other than the human signal component. Now, when the input signal X is expressed by the following formula, x −A cos aL+B cos bt
The component corresponding to the so-called third-order distortion of -■x3 is expressed by the following equation using the 0 equation.

x3=(^cos at +Rcos bt)3=
1/4 (A3cos 3at+B" cos 3bt
)+3/4 (A2B cos(2aib)t + A
B2cos(2b:!=a)t l+3/4 (A'
cos at + B3cos bt )+3/2
(AB2 cos at + BA2 cos
bt) - In the right side of the formula, the first term is the third harmonic component, the second term is the intermodulation component, the third term is the fundamental nonlinear component, and the fourth term is the cross modulation component. Furthermore, in the equation (2), if the first term is an unmodulated pilot signal and the second term is a television signal, then the video signal is 5(t)
As, B = 1 15(t)
...■ I can express it. A, a, b are constants. Therefore, the cross-modulation component AB2cos at
Focusing on , using the formula ■, 8B2cos at = A (s(t)2+ 2s(t) + 1) c
os at −■. This is because the video signal component and its second component are included in the viroft signal envelope of the line amplifier output.
This shows that the next distortion component appears. On the other hand, the video signal 3 (t) has very strong components at the horizontal scanning frequency and frequencies that are integral multiples thereof. Therefore, by detecting the pilot signal of the line amplification output and detecting an increase in the level of the horizontal scanning frequency and its integral multiple frequency components, it is possible to detect an increase in distortion of the amplifier. Note that this also applies when a plurality of television signals are input to the line amplifier.

In FIG. 1, a terminal device 5 is a so-called 1-way addressable terminal device. If subscribers want to watch a program, they apply by phone or mail. On the other hand, a specific address is set for each terminal device. For example, in the case of the terminal device 5, the reception and demodulation circuit 27 receives a downlink command to the own terminal, and the keyboard 30, control circuit 38, and descrambler 31 The video signal of the paid program for which the user has already subscribed is obtained at the video output terminal 7. Therefore, the descrambler 4 includes a channel selection function.

In FIG. 1, a signal containing an unmodulated pilot signal together with a television signal is input as a downstream signal to an input terminal l. A pilot signal that has undergone cross modulation due to the nonlinearity of a relay amplifier in the transmission path is extracted by a first filter 18, amplified by a pilot signal amplifier 19, and detected by a detector 20. The detector 20 may be of any type as long as it can extract the envelope, such as a half-wave rectifier type, a full-wave rectifier type, a square law detector, or a synchronous detector using a PLL or the like.

As mentioned above, the output of the detector 20 includes the horizontal scanning frequency and frequency components that are integral multiples thereof, and the second filter 9 passes one or more of these components. . If the output signal of the second filter 9 is called a detection signal, the second filter 9 serves to improve the S/N ratio of the detection signal and stabilize the distortion increase detection operation.

Fig. 2 (al to ('b)) shows an example of the frequency characteristics of such a second filter 9. However, in Fig. 2, f□ indicates the horizontal scanning frequency. Fig. 2 +a+
The filter does not allow direct current components to pass through, and although it is disadvantageous in terms of improving the S/N ratio of the detection signal, it can also cope with the occurrence of distortion due to excessive input of signals other than television signals. Figure 2 (bl~(dl) uses the fact that, as mentioned above, when a television signal is included in the downlink signal, the detection signal has very strong components at the horizontal scanning frequency and frequencies that are integral multiples thereof. This figure shows an example of the characteristics of the second filter that can improve the S/N ratio of the detection signal.

The detection signal obtained in this way is sent to the detection signal amplifier l.
After being amplified by O, the level is detected by a level detector 11. If the detection signal level becomes abnormally high,
The transmission modulation circuit 28 generates a failure detection signal that can be recognized by the monitoring terminal of the terminal device that has detected the failure, and is transmitted as an upstream transmission signal to the monitoring terminal at the head end. The fault detection signal may, for example, give a different carrier frequency to each terminal device, change the output, frequency, or phase depending on whether or not a fault has occurred, or may be modulated with a digital signal.

As described above, according to this embodiment, the first filter extracts the pilot signal cross-modulated due to the distortion of the repeater amplifier, the detector extracts the envelope of this pilot signal, and the horizontal scanning frequency and its integral multiple frequency. a second filter that passes one or more of the components;
By providing a level detector and a transmission modulation circuit in a terminal device, it is possible to directly and accurately detect a distortion increase fault in a relay amplifier by detecting an increase in the level of the cross-modulation component from the television signal to the pilot signal. At the monitoring terminal at the head end, it is possible to know which transmission route a failure has occurred.

A second embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 is a circuit diagram of a terminal device of a distortion monitoring device showing a second embodiment of the present invention. In the same figure, 21 is a viroft signal amplification/detection section, 9 is a second filter, 10 is a detection signal amplifier, and 11 is a level detector, which constitutes a total failure detection section 22 in the same manner as in the configuration shown in FIG. Further, 1 is an input terminal, 7 is a video output terminal, 8 is a control circuit, 27 is a reception demodulation circuit, 28 is a transmission modulation circuit, and 29 is an upper and lower signal separation filter, which is the same as the configuration shown in Fig. 1. be. The difference from the configuration shown in FIG. 1 is that the output of the level detector 11 is input to the transmission modulation circuit 28 via the control circuit 8. Note that the terminal device 5 is configured as described above.

The operation of the terminal device of the distortion monitoring device configured as described above will be described below.

The method for detecting the total increase is exactly the same as in the first embodiment, and when the distortion of the downstream signal increases, the output of the level detector 11 increases. The difference from the first embodiment is that the failure detection signal is transmitted not in one direction, but in both directions, while exchanging commands. That is, the monitoring terminal at the head end sends a downlink command that can identify which terminal device it is as a downlink signal. The control circuit 8 of the terminal device 5 uses the reception demodulation circuit 27 to decode this lower recommand, and as a response, transmits an uplink command containing information from the level detector, that is, information on the presence or absence of distortion disturbance. It is sent back to the monitoring terminal using the modulation circuit 2nd. In this way, the monitoring terminal can know whether each terminal device has detected a distortion fault. The communication procedure between the monitoring terminal and each terminal device may be a polling method that constantly calls each terminal device in turn, or a method in which the terminal device sends a signal to the monitoring terminal when a failure occurs and then starts communication. It may be a contention method or a combination of both.

Note that this terminal device 5 may be a so-called 2-way addressable terminal device that can provide pay-per-view services.

In other words, similarly to the transmission of the fault detection signal, the reception demodulation circuit 27
, the transmission modulation circuit 28 and the control circuit 8 are shared to perform two-way communication with the head end, and in response to instructions from the keyboard 30, pay programs can be selected and descrambled and viewed using the descrambler 31, and charges 1. It will be done according to the time given.

As described above, by manually controlling the output of the level detector in the terminal equipment to the transmission modulation circuit via the circuit, it becomes more flexible when expanding the system, such as adding terminal equipment that has a full fault detection section. You can build a system with Furthermore, since the reception demodulation circuit, transmission modulation circuit, and control circuit are shared for the transmission of the failure detection signal and the transmission of channel selection/charging information, it is economical.

In addition, in both the first and second embodiments, instead of providing all the fault detection sections 22 in all terminal devices, it is also possible to provide the all fault detection sections 22 only in terminal devices located at positions where the fault detection effect is large. good. For example, since most failures occur in relay amplifiers, if there are multiple terminal devices further downstream from the relay amplifier at the end of the transmission path, all failure detection units are required for only one of these terminal devices. Just by installing 22, the same fault detection ability can be obtained.

By doing so, the system can be realized at a lower cost.

Further, in the first embodiment, the terminal device having the total failure detection section may be a simple terminal device without the reception demodulation circuit 27, the control circuit 38, the keyboard 30, and the descrambler 31, and may also be a It may be a special terminal device that does not have the output terminal 7 and only has a fault detection function. Similarly, in the second embodiment, the terminal device including the entire fault detection section may be a simple terminal device without the keyboard 30 and the descrambler 31, and may also be a simple terminal device without the video output terminal 7, and the fault detection It may be a special terminal device having only one function.

Effects of the Invention As described above, the present invention includes an unmodulated pilot signal in the downlink transmission signal, and in the terminal device at the end of each branched transmission path of the transmission system, the transmission path to the terminal device includes an unmodulated pilot signal. a first filter that extracts the pilot signal that has been cross-modulated due to nonlinearity of a relay amplifier; a detector that can extract the envelope of the biloft signal that has passed through the first filter; and a DC output signal of the detector output signal. a second filter that does not allow components to pass; a level detector that detects the level of the detection signal that has passed through the second filter; and a terminal that detects an increase in distortion based on the increase in the level of the detection signal and monitors the failure detection signal. By providing a means for transmitting the pilot signal from the transmitted television signal, the intermodulation component from the pilot signal is extracted, and its level is monitored at the end of the transmission network, thereby accurately detecting distortion increase failures in the repeater amplifier. becomes possible.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a circuit of a terminal device of a distortion monitoring device according to a first embodiment of the present invention, FIG. 2 is a characteristic diagram showing an example of frequency characteristics of a second filter 9, and FIG. FIG. 4 is a block diagram showing an example of a CATV transmission network, and FIG. 5 is a circuit block diagram of a relay amplifier of a conventional distortion monitor. 1...Input terminal, 5...Terminal device, 7
......Video output terminal, 8.38...Control circuit, 9...Second filter, 10...
Detection signal amplifier, 11...Level detector, 18
......First filter, 19...Pilot signal amplifier, 20...Detector, 21...
... Pilot signal amplification detection section, 22 ... Distortion disturbance detection section, 27 ... Reception demodulation circuit, 28 ...
... Transmission modulation circuit, 29 ... Upper and lower signal separation filter, 30 ... Keyboard, 31 ...
・Descrambler. Name of agent: Patent attorney Toshio Nakao and one other person
(Figure 2)

Claims (5)

[Claims] (1) A wired transmission system that extends in a dendritic manner from a head end, and includes an unmodulated pilot signal in the downlink transmission signal, and in a terminal device at the end of each branched transmission path of the transmission system, the terminal device a first filter that extracts the pilot signal that has been cross-modulated due to the nonlinearity of the relay amplifier on the transmission path; a detector that can extract the envelope of the pilot signal that has passed through the first filter; and a detector that can extract the envelope of the pilot signal that has passed the first filter; a second filter that does not pass the DC component of the device output signal; a level detector that detects the level of the detection signal that has passed through the second filter; and a level detector that detects an increase in distortion based on an increase in the level of the detection signal, and detects a fault. 1. A distortion monitoring device comprising: means for transmitting a signal to a monitoring terminal. (2) The distortion monitoring device according to claim 1, wherein the transmission system is a CATV transmission system. (3) Claims characterized in that the second filter is capable of passing one or more frequency components of the horizontal scanning frequency of the television signal transmitted as a downstream signal and frequencies that are integral multiples thereof. The distortion monitoring device according to item 1 or 2. (4) The distortion monitoring device according to any one of claims 1 to 3, wherein the means for transmitting the failure detection signal to the monitoring terminal uses upstream transmission of the transmission system. (5) The terminal device and the monitoring terminal have bidirectional communication means, and transmit fault detection signals by exchanging commands with each other.
2. Distortion monitoring device according to item 1 or 2.