JPS6040070Y2 - Central monitoring device for CATV system - Google Patents

Description

[Detailed Description of the Invention] This 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:
VHF low channel, VHF high channel, and UH output from the headend connected to the common antenna
The TV signals of all the F channel broadcast channels are transmitted to the terminal, several main line amplifiers are inserted in the middle, and multiple branch transmission lines are separated from each main line amplifier.
In this way, television signals are transmitted to multiple 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. This required a large number of elements, and a stable monitoring operation could not be expected.

This device effectively uses the TV signal of the broadcast channel as a monitoring signal to enable monitoring with actual images, prevents the monitoring failure display from malfunctioning after the broadcast waves stop at night, etc., and furthermore A CAT that makes it possible to identify monitoring signals for each section of a transmission trunk divided into many trunk expansion types even if the number is small, making it easy to understand the location of failure and the extent of the failure.
The purpose is to obtain a centralized monitoring device for the V system.

Next, this invention will be explained with reference to an embodiment drawing. In FIG. 1, 1 is a common antenna of the CATV system, and 2 is a head that adjusts the level of the TV signal received by this antenna 1 for each broadcast channel and sends it to the transmission trunk 3. End, 4
-1 to 4-n are main line amplifiers inserted in the transmission main line 3;
is a terminator of 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 inside it receives the television signals of each broadcast channel from the output end of the head end 2, and outputs the signals when the level is above a predetermined value. level determiners 7-1 to 7-7 (for seven channels in this example) each having a band-pass filter that generates Another level determiner 21-1 to 21-7 each having a similar bandpass filter that produces an output when the level is above the level, and the level determiner 7-1 to 7-7 for each broadcast channel.
7 and another level determiner 21-1 to 21-7, and when there is no output from either one, the indicators 8-1 to 21-7
Exclusive OR circuit 22-1 that operates 8-7 correspondingly.
~22-7 are provided, and these head end 22-7 are provided.
The output status of each broadcast channel is monitored.

Incidentally, a monitor television receiver 9 connected to the output side of the head end 2 is also provided in the monitoring receiving device, so that the head end output can be monitored using the actual image receiving screen. .

In this invention, the auxiliary transmission line 1 is provided by another cable conduit preferably installed in parallel along the transmission main line 3.
0 is installed, and one end of the cable is connected to the monitoring/receiving device 6.

Also, a main line amplifier 4 connected to the terminal of the transmission main line 3
-n only, the bandpass filter 11-
A signal sending device 12- consisting of a down converter 13 and a down converter 13.
n are provided, and other intermediate trunk amplifiers 4-1 to 4-n-
1, each bandpass filter 1 is placed in each neighborhood.
1-1 to 1l-n-1 and level determination devices 14-1 to 1
4-n-1 and switching devices 15-1 to 15-n-
1 and signal transmitting devices 12-1 to 12-n-1 each including oscillators 16-1 to 16-n-1.

Bandpass filter 11 in signal sending device 12-n
-n extracts, for example, a television signal of a specific one of the broadcast channels from the branch output of the main amplifier 4-n within the channel band (6 MHz width), and the down converter 13 extracts this extracted TV signal. The auxiliary transmission line "0" converts the frequency of the television signal of a specific broadcasting channel into a lower frequency monitoring television signal while maintaining its frequency band.
and reversely transmits it to the monitoring receiving device 6.

In this case, the television signal extracted from the terminal mains amplifier 4-n is reversely transmitted via the auxiliary transmission line 10 from the terminal of the farthest distance interval to the monitoring and receiving device 6, and is therefore lowered by the down converter 13. Converting to 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 3 is used, the television signal extracted and reversely transmitted by the signal transmitter 12-n may be of any broadcast channel.

Each intermediate signal sending device 12-1.12-2 to 12-n-
1, the bandpass filter 11-1.11-2
~1l-n-1 are the corresponding main line amplifiers 4-1.4-
A signal of one frequency, such as a video signal carrier wave, in a TV signal of an arbitrary broadcasting channel is extracted in a narrow band from the branch outputs of 2 to 4-n-1, and this narrow band signal is passed to a level determination device 14-. 1.14-2 to 14-n-1.

In the illustrated example, the first stage and second stage main line amplifiers 4-1.4-
extracting the video signal carrier wave of the television signal of the 12th channel from 2, extracting the video signal carrier wave of the television signal of the 10th channel from the third and fourth stage trunk amplifiers (not shown), Similarly, the video signal carrier wave of the third channel television signal is extracted from the trunk amplifier 4-n-1 one stage before the terminal as several groups.

Each level determination device 14-1.14-2 to 14-n-1 determines whether the level of the narrowband signal received at the input is higher than a predetermined value, and only during the period when the input of the input is higher than the predetermined level. Output switching device 15-1.15-2~15
−n−1.

Each switching device outputs the outputs of the oscillators 16-1, 16-2 to 16-n-1, which have different oscillation frequencies from each other, to the auxiliary transmission line 10 as a monitoring signal only when they are in operation, and is activated when the input is no longer available. For example, it consists of an analog switching element, etc., which stops the transmission of the oscillator output to the auxiliary transmission line 10.

The oscillation frequencies of each of the oscillators 16-1, 16-2 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 transmitting device 12-n, As a result, the terminal signal sending device 1
The monitoring television signal from 2-n and each monitoring signal from the intermediate signal transmitting devices 12-1, 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 terminal, and furthermore, the frequency of the monitoring television signal from the terminal 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 17-1.17 that detects the above-mentioned monitoring television signal and each monitoring signal from the auxiliary transmission line 10 based on their respective frequencies, and produces an output when the signals are at or above a predetermined level. -2 to 17-n and each output of this detection device as one input, and for each detection device, each monitoring TV signal and the extracted TV signal that is the source of the monitoring signal are based on which broadcast channel. Level determiners 7-1゜7-2 to 7-7 detect the signals corresponding to the head-end TV signals of the respective corresponding broadcast channels.
n exclusive OR circuits 23-1. A monitoring display 18 activated by the output generated when
-1° 18-2 to 18-n, an up-converter 19 which extracts the above-mentioned monitoring television signal from the auxiliary transmission line 10 and returns it to the original frequency band, and the output of the up-converter 19 is extracted as the above-mentioned monitoring television signal. Another monitor television receiver 20 for receiving the specified broadcast channel
Further features are provided.

In other words, each signal sending device 12-1.1 during normal operation.
Each monitoring signal and monitoring television signal from 2-2 to 12-n are detected by a corresponding detection device 17-1, 17-2 to 17, respectively.
-n, and this detection output and each level judger? -1, 7-2 to each channel TV signal detection output from 7-7, each exclusive OR circuit 23-1.23-2
~23-n signals are given correspondingly to both of the input signals, so each exclusive OR circuit outputs each display 1 without producing an output.
8-1.18-2 to 18-n remain inactive.

The monitoring television signal from the terminal signal transmitting device 12-n is also returned to the frequency band of the original specific broadcast channel by the up converter 19 and sent to another monitor television receiver 20.
An image is received.

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 transmitting device drops dramatically or is interrupted, and all the corresponding display devices in the latter stages operate, and the received image on the monitor television receiver 20 also deteriorates in image quality or disappears. .

This makes it possible to determine which main line amplifier has caused the failure.

In other words, a line failure or a failure in the main line amplifier causes the output of the signal sending device downstream of the failure point to be cut off, causing the corresponding detection device to switch to the exclusive OR circuits 23-1 to 23-n.
One of the inputs to the corresponding one of the display devices 18-1 to 18-n is cut off, and as a result, the exclusive OR circuit with one input produces an output and operates the corresponding one of the display devices 18-1 to 18-n. It is.

This fault display operation is performed when broadcast waves are present,
When there is no broadcast wave, level determiners 7-1 to 7-7
Since neither of the detection devices 17-1 to 17-n produces an output, each exclusive OR circuit also does not produce an output, and this prevents the display from operating when there is no broadcast wave, such as at night. There is.

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 the number of main line amplifiers in the main line is large, a narrow band frequency signal such as a video signal carrier wave of a television signal of each broadcast channel can be used as a monitoring signal as it is.

FIG. 2 shows an example of this case, where the broadcast channel is 1. Third. 4th. 6th. 8th. This shows a system configuration in which there are a total of seven channels (10th and 12th) and seven main line amplifiers.

In the second, the main line amplifier 4- which is closest to the head end.
1 is provided with a signal transmitting device 12'-1 consisting of a narrowband bandpass filter (or tuner) 11'-1 that is tuned to and extracts the video signal carrier wave of the television signal of the 12th channel. In the vicinity of the main line amplifier 4-2 in the next stage, there is also a narrowband bandpass filter (or tuner) 11'-2 that is tuned to and extracts the video signal carrier wave in the television signal of the 10th channel. A signal transmitting device 12'-2 is provided, and in the same manner, a signal transmitting device comprising a bandpass filter 11'-7 that extracts the television signal of the first channel as it is only to the terminal trunk amplifier 4-7. 12'-7 is provided.

That is, from the terminal signal device 12'-7, the television signal of one channel itself is transmitted as a monitoring television signal via the auxiliary transmission line 10 to the auxiliary transmission line 1 as a monitoring television signal.
0 to the monitoring/receiving device 6, and from each of the other signal transmitting devices 12'-1, 12'-2...
Each video signal carrier wave of channel, 10th channel, etc. is reversely transmitted to the monitoring receiving device 6 via the auxiliary transmission line 10 as a narrowband monitoring signal.

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 determiner with a bandpass filter 17'-1, 17'-2, . . .
The level of the monitoring television signal is determined separately by the level determiner 17'-1 for the final stage, and the frequency is converted to one of the empty channels or VHF channels via the converter 24. is input to the monitor television receiver 9.

Each level determiner 17'-1, 17'-2 to 17'-7 displays an indicator 18'-1 when the input signal level is above a predetermined value.
, 18'-2 to 1B'-7.

Other operations are the same as in FIG. 1.

As mentioned above, according to this invention, since the TV signal of the broadcast channel is returned from only the main line amplifier at the end for image monitoring, the TV signal of any broadcast channel can be returned from the other intermediate main line amplifiers. It is only necessary to return the monitoring signal whose signal content is to judge the level of the signal.Therefore, these monitoring signals do not require a wide band, so a large number of monitoring signals can be handled within a certain frequency range, making it suitable for broadcasting at night, etc. The display device will not malfunction when the waves stop, and even if there are a large number of main line amplifiers, line monitoring using the television signal of the broadcast channel can be effectively carried out.

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. The monitoring signal may be converted into an optical signal and reversely transmitted with low loss.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a CATV system according to one embodiment of this invention, and FIG. 2 is a block diagram showing another embodiment. 3...Transmission trunk line, 4-1.4-2~4-n...
... Main line amplifier, 6 ... Monitoring and receiving device, 1
0... Auxiliary transmission line, 11-1.11-2 to 11
-n...Band pass filter, 12-1.12
-2 to 12-n... Signal sending device, 13...
...down converter, 14-1.14-2 to 14-
n-1... Level determination device, 15-1.15-
2-15-n-1...Switching device, 16
-1.16-2 to 16-n-1...Oscillator, 1
7-1.17-2 to 17-n...detection device, 1
8-1.18-2 to 18-n... Indicator, 19
...Up converter, 20...Monitor television receiver, 23-1 to 23-n...Exclusive OR circuit.

Claims (1)

[Scope of utility model registration request] An arbitrary specific broadcasting channel is assigned to each of a plurality of trunk amplifiers inserted into the transmission trunk of a CATV system, and the TV signals obtained from the branch outputs of the trunk amplifiers are allocated to the trunk amplifier. A signal transmitting device that extracts only the television signal of a specific broadcast channel and outputs a signal of a unique frequency to the main line amplifier in accordance with its output level is provided near each main line amplifier, and the transmission main line and In parallel, a separate auxiliary transmission line is laid, the individual signals from each signal sending device are reversely transmitted via the auxiliary transmission line, and the individual signals reversely transmitted are transmitted from the auxiliary transmission line. A monitoring/receiving device is provided on the head end side of the transmission trunk for identifying and monitoring the output status of each main line amplifier based on the respective unique frequencies. an exclusive OR circuit whose inputs are the output and the head end output of the specific broadcasting channel assigned to the trunk amplifier corresponding to the individual signal; and a monitoring display controlled by the output of the exclusive OR circuit. A central monitoring device for a CATV system, characterized by being equipped with a monitor.