JPS6053956B2 - Central monitoring device for CATV system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a centralized monitoring device for the main line of a CATV system.

The transmission trunk line in a dendritic wiring CATV system includes:
The TV signals of all broadcast channels (HF Roach Channel, High Channel, and U8 Channel) output from the head end connected to the common antenna are transmitted to the terminal, and several main line amplifiers are installed along the way. A plurality of branch transmission lines are branched from each trunk amplifier after insertion, and in this way, television signals are transmitted to a large number of terminals via each branch transmission line.

If a failure occurs on this transmission trunk line, such as a cable break or trunk amplifier malfunction, the TV signal will not be transmitted from the failure point to the rear (closer to the end), and the impact on subscribers will be extremely large. , its monitoring is particularly important. Various methods have been used to monitor faults in transmission trunk systems, but these systems have complex mechanisms and operations, such as returning a pilot signal from each trunk amplifier and distinguishing between each trunk amplifier using a time-division method. The situation is such that a stable monitoring operation cannot be expected since it requires many elements.

This invention effectively utilizes the television signal of a broadcast channel as a monitoring signal and monitors the actual image. In addition, even if the number of broadcast channels is small, it is possible to identify the monitoring signals for each section of the transmission trunk divided into many trunk amplifiers, making it possible to understand the location of failure and the extent of the failure. A centralized monitoring device for CATV systems that makes it easy to understand. The purpose is to obtain.

Next, this invention will be explained with reference to the drawings of the embodiments. In FIG. 1, 1 is a common antenna of a CATV system, and 2 is a TV signal received by this antenna 1, which adjusts the level of each broadcast channel and sends it out to a transmission trunk 3. head end,
4-1 to 4-n are main line amplifiers inserted in the transmission main line 3;
5 is a terminator for the transmission trunk line 3;

In the illustrated example, there are n main amplifiers, and amplifiers 4-1 to 4-n are sequentially arranged far from the head end, and each amplifier is provided with a plurality of branch outputs. A monitoring/receiving device 6 is connected to the transmission main line 3 on the side of the head end 2, and a level determiner 7-- having a band-pass filter for each channel TV signal from the head end 2 is connected therein.
1 to 7-7 (in this example, for 7 channels), and is activated when the input becomes below a predetermined level.
-1 to 8-7, and a monitor television receiver 9 for receiving the television signal.In the CATV system as described above, in the present invention, preferably another An auxiliary transmission line 10 is laid along the route using a cable conduit or the like, and one end of the line is led into the monitoring/receiving device 6 .

Also, a main line amplifier 4 connected to the terminal of the transmission main line 3
-n is provided with a signal transmitter 12-n consisting of a bandpass filter 11-n and a down converter 13,
In the vicinity of each of the other intermediate main line amplifiers 4-1 to 4-n-1, band pass filters 11-1 to 11-n-1 are provided, respectively.
Level determination devices 14-1 to 14-n-1, switching devices 15-1 to 15-n-1, and oscillators 16-1 to 1
6-n-1, signal transmitting devices 12-1 to 12-n.
-1 is provided. In the signal transmitter 12-n, the bandpass filter 11-n converts the television signal of a specific one of the broadcast channels from the branch output of the main amplifier 4-n into the channel bandwidth (6 MH).
The down converter 13 frequency-converts the extracted television signal of the specific broadcasting channel into a monitoring television signal of a lower frequency while maintaining its bandwidth, and outputs it to the auxiliary transmission line 10. It is reversely transmitted to the monitoring receiving device 6.

In this case, the television signal extracted from the main line amplifier 4-n at the terminal is reversely transmitted from the terminal at the farthest distance interval to the monitoring/receiving device 6 via the auxiliary transmission line 10, and is therefore further transmitted to the down converter 13. Converting to a lower frequency is advantageous in terms of transmission loss. When the down converter 13 is not used, such as when the distance from the head end side to the end is relatively short, the TV signal extracted by the band pass filter 11-n is the TV signal of the lowest frequency band among the broadcast channels. However, as long as the down converter 13 is used, the television signal extracted and reversely transmitted by the signal transmitter 12-n may be of any broadcast channel. In each signal sending device 12-1, 12-2 to 12-n-1, band pass filter 11-1, 11-2 to 1
1-n-1 are the corresponding main line amplifiers 4-1, 4-2~
A single frequency signal such as a video signal carrier wave in a television signal of an arbitrary broadcasting channel is extracted from the branch output of 4-n-1 in a narrow band, and this narrow band signal is passed to the level determination device 14.
-1, 14-2 to 14-n-1.

Each level determination device determines whether the level of the narrowband signal received at the input is higher than a predetermined value, and outputs the output to the switching device 1 only while the input is higher than a predetermined level.
5-1, 15-2 to 15-n-1. Each switching device outputs the outputs of the oscillators 16-1, 16-2 to 16-n-1, each having a different oscillation frequency, to the auxiliary transmission line 10 as a monitoring signal only during operation.
It is made up of, for example, an analog switching element that stops operating and cuts off transmission of the oscillator output to the auxiliary transmission line 10 when there is no input. The oscillation frequencies of each of the oscillators 16-116-2 to 16-n-1 are different from each other and also different from the frequency band of the monitoring television signal from the terminal signal transmitter 12-n,
As a result, the monitoring television signal from the signal transmitter 12-n and each monitoring signal from each signal transmitter 121, 12-2 to 12-n-1 are frequency-divided and monitored via the auxiliary transmission line 10. It will be reversely transmitted to the receiving device 6. In this case, the frequency assignment of each oscillator should be determined so that the oscillation frequency decreases as it moves away from the head end and approaches the end, and furthermore, the frequency of the monitoring television signal from the end should be determined to be the lowest.Transmission loss It is advantageous in terms of Within the monitoring and receiving device 6, there is a detection device 17-1 which detects the above-mentioned monitoring television signal and each monitoring signal from the auxiliary transmission line 10 based on their respective frequencies, and generates an output when the signal falls below a predetermined level. , 17-2 ~ 17-
n, indicators 18-1, 18-2 to 18-n whose operation is controlled by the output of each detection device, and an auxiliary transmission line 10.
an up-converter 19 for extracting the monitoring television signal from the source and returning it to the original frequency band; and another monitor television receiver for receiving a specific broadcast channel extracted as the monitoring television signal by the output of the up-converter 19. A machine 20 is further provided. That is, during normal operation, each signal sending device 12-1, 12-2 to 12-n
The monitoring signals from -1 are the corresponding detection devices 17-1,
17-2 to 17-n-1 and each display 18-1
, 18-2 to 18-n-1, and the monitoring television signal from the signal transmitter 12-n is detected by the detection device 17.
-n to prevent the operation of the display 18-n, and at the same time, the up-converter 19 returns the frequency band to the original specific channel, and the image is received by another monitor television receiver 20. When the level of the branch output of one of the main line amplifiers drops due to a disconnection or failure of the amplifier, a monitoring signal is sent from the signal sending device connected to each of the subsequent main line amplifiers, including that main line amplifier. At the same time, the level of the monitoring television signal from the terminal signal transmitter drops drastically or is interrupted, and all the corresponding displays for subsequent stages are activated, and the received image on the monitor television receiver 20 also deteriorates in image quality or is not visible at all. It disappears. This makes it possible to determine at which main line amplifier the fault has occurred. In the embodiment shown in Fig. 1, each of the intermediate main line amplifiers except for the terminal main line amplifier is provided with an oscillator with a unique frequency, and the output of this oscillator is used as a monitoring signal. If there are more amplifiers than the number of main line amplifiers in the main line, a narrow band frequency signal such as a video signal carrier wave in a television signal of each broadcast channel can be used as a monitoring signal as it is.

Figure 2 shows an example of this case, where there are a total of 7 broadcast channels, 1st, 3rd, 4th, 6th, 8th, 10th, and 12th, and 7 main line amplifiers. The system configuration in one case is shown. In FIG. 2, a narrowband bandpass filter (or tuner) is installed near the main line amplifier 7 4-1 closest to the head end, which is tuned to and extracts the video signal carrier in the 12th channel television signal. )1
A signal transmitting device 12''-1 consisting of 11 is provided in the vicinity of the next-stage trunk amplifier 4-2, and is similarly tuned to the video signal carrier wave in the television signal of the 10th channel. Narrowband bandpass filter (or tuner) to extract 1
A signal transmitting device 12''-2 consisting of a bandpass filter 12''-2 is provided, and in the same manner, a bandpass filter 12''-2 extracts the TV signal of the first channel as it is only to the terminal trunk amplifier 4-7. A signal transmitter 12''-7 is provided. That is, from the signal transmitter 12''-7, the first channel television signal itself is reversely transmitted as a monitoring television signal to the monitoring and receiving device 6 via the auxiliary transmission line 10.
Other signal sending devices 12''-1, 12''-2...
From there, each video signal carrier wave of the 12th channel, 10th channel, etc. is transmitted to the auxiliary transmission line 1 as a narrowband monitoring signal.
0 to the monitoring/receiving device 6. The reason why broadcast channels closer to the end are assigned to lower frequency broadcast channels is because, as mentioned above, it is advantageous in terms of transmission loss during reverse transmission. In the monitoring/receiving device 6, each monitoring signal is passed through a level judger 17''-1, 17''- with a band-pass filter.
2, respectively, and only the monitoring television signal is level determined by the final stage level determiner 17''-7, and the monitor television receiver 20
is input. Each level determiner 17″-1, 17″-2
〜17″-7 indicates the indicators 1 ``-1, 18″-2〜 which are respectively connected to − when the input signal level falls below a predetermined value.
18"-7. As described above, according to the present invention, since the TV signal of the broadcast channel is returned only from the terminal main line amplifier for image monitoring, other intermediate trunks; The device only needs to return a monitoring signal whose signal content is to judge the level of the TV signal of a given broadcast channel. Therefore, each of these monitoring signals does not require a wide band, so it is possible to send a large number of monitoring signals within a fixed frequency band. Even if there are a large number of main line amplifiers, monitoring of broadcast channels using television signals can be carried out effectively.

In each of the above-mentioned embodiments, the monitoring television signal and the monitoring signal are reversely transmitted as electrical signals to the monitoring receiving device via the auxiliary transmission line, but the auxiliary transmission line is used as an optical cable to transmit the monitoring television signal and the monitoring signal. may be converted into an optical signal and reversely transmitted with low loss.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a CATV system according to one embodiment of the present invention, and FIG. 2 is a block diagram showing another embodiment. 3...Transmission trunk line, 4-1, 4-2 to 4-n...
・Trunk line amplifier, 6...Monitoring/receiving device, 10...
...Auxiliary transmission line, 11-1, 11-2 to 11n...
...Band pass filter, 12-1, 12-2~1
2-n-1... Signal sending device, 12-n...
... Signal transmitter, 13 ... Down converter, 14-1, 14-2 to 14-n-1 ... Lebel determination device, 15-1, 15-2 to 15-n -1...
・Switching device, 16-1, 16-2 to 16-n-
1... Oscillator, 17-1, 17-2 to 17-n
...Detection device, 18-1, 18-2 to 18-n
...display unit, 19...up converter, 20...monitor television receiver.

Claims (1)

[Claims] 1. A plurality of main line amplifiers inserted into a transmission trunk line of a CATV system are each assigned a unique frequency, and at least one of the main line amplifiers connected to the end of the transmission trunk line is assigned a unique frequency. A specific broadcasting channel in a frequency band different from the individual frequency assigned to the trunk amplifier at the terminal is assigned, and the TV signal of the specific broadcasting channel is extracted from the branch output of the terminal trunk amplifier and monitored. Connect a signal transmitter that outputs a TV signal to another intermediate amplifier, and use the above-mentioned signals specific to the main amplifier depending on the output level of the TV signal obtained from its branch output. Connecting signal transmitting devices that output monitoring signals each having a unique frequency, and laying a separate auxiliary transmission line in parallel with the transmission main line,
The monitoring television signal from the signal transmitter and each monitoring signal from each of the signal transmitting devices are reversely transmitted through the auxiliary transmission line, and the reversely transmitted monitoring television signal and each monitoring signal are 1. A centralized monitoring device for a CATV system, characterized in that a monitoring receiving device for receiving the information and monitoring the output status of each main line amplifier is provided on the head end side of the transmission main line. 2 A signal transmitter connected to the trunk amplifier at the end of the transmission trunk extracts the television signal of the lowest frequency band among the broadcasting channels and outputs it as a monitoring television signal. Each signal transmission device connected to the main amplifier extracts signals of different narrowband frequencies from the television signals of the different broadcasting channels except for the channel in the lowest frequency band, and outputs them as monitoring signals. and each signal sending device is provided with a frequency selection characteristic so that the frequency of each monitoring signal becomes lower as the signal sending device is connected to the trunk amplifier near the end of the transmission trunk line. A centralized monitoring device for a CATV system according to claim 1, characterized in that: 3. Each of the above-mentioned signal transmission devices extracts a television signal of an arbitrary broadcasting channel from the branch output of the main line amplifier to which it is connected, and only when the output level of this television signal is equal to or higher than a predetermined level, outputs the television signal from the oscillator provided in each. The monitoring signal of the individual frequency is outputted to the auxiliary transmission line, and the individual frequency of each monitoring signal is gradually lowered as the signal sending device connected to the trunk amplifier near the end of the transmission trunk line becomes lower. 2. A centralized monitoring device for a CATV system according to claim 1, wherein the output frequency of each of the oscillators is set so that: 4 The signal transmitter converts the television signal of a specific broadcasting channel extracted from the main line amplifier at the terminal to a lower frequency and a frequency band different from that of the monitoring signal, and sends it as a monitoring television signal to the auxiliary transmission line. Claim 1, characterized in that the monitoring receiving device is equipped with an up-converter that returns the monitoring television signal to its original frequency band and inputs it to the monitor television receiver. A centralized monitoring device for a CATV system as described in 2.