JPS6053955B2 - 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 in a dendritic CATV system includes the VHF low channel, the VHF high channel, and the U
The television signals of all the broadcast channels of the HF channel are broadcast to the terminal, several main line amplifiers are inserted in the middle, and a plurality of branch transmission lines are separated from each main line amplifier, and in this way each Television signals are transmitted to multiple terminals via branch transmission lines.

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 using a time-division method to identify each trunk amplifier. The situation is such that a stable monitoring operation cannot be expected since it requires many elements.

This invention makes it possible to effectively use the television signal of a broadcast channel as a monitoring signal to monitor actual images, and even if the number of broadcast channels is small, the transmission main line divided into many main line amplifiers can be used. It is an object of the present invention to provide a centralized monitoring device for a CATV system, which makes it possible to identify monitoring signals for each section of the system, and makes it easy to grasp the location where a fault occurs and the extent of the fault.

Next, the present invention will be explained with reference to the drawings of the embodiments. In Fig. 1, 1 is a common antenna of the CATV system; 4-1 to 4-n are trunk amplifiers inserted into the transmission trunk line 3, and 5 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 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 are provided, and a monitor television receiver 9 for receiving the above-mentioned television signals is also provided. In the CATV system as described above, in the present invention, an auxiliary transmission line 10 is laid along the transmission main line 3, preferably by another cable conduit, and each main line amplifier 4-1, 4-2
The TV signal of the first channel is output as a monitoring TV signal by band pass filters 11-1, 11-2 to 11-n which pass only the TV signal of an arbitrary broadcasting channel, for example, the first channel, from the branch output of 4-n. Extracted.

This band pass filter 11-1, 11-2 to 11-n
each constitute a part of the signal transmitting devices 12-1, 12-2 to 12-n, and each signal transmitting device is installed near the corresponding main line amplifier 4-1, 4-2 to 4-n. be done. In each signal sending device, band pass filters 11-1, 11-
The first channel television signal extracted at .2 to 11-n has a lower unique frequency. several bands, e.g. 90-96M
The signal transmitting device 12 transmits the television signal of the first channel of Hz.
-1 to 1 to 7 MHz, and signal transmitter 12-2 to 7 MHz.
~13MHz, each downconverter 13-
1, 13-2 to 13-n.

The output signals of these down converters have unique frequency bands that differ from each other for each corresponding trunk amplifier, and the output signals are further passed through band compressors 14-1 and 14-1 as necessary.
4-2 to 14-n, the original 6r1V1HZ bandwidth is compressed to, for example, about 2MH2, and then transmitted to the auxiliary transmission line 10 and reversely transmitted to the monitoring/receiving device 6.

In this invention, band pass filters 11-1, 11-2
The broadcast signal of any channel can be selected as the specific channel to be extracted in ~11-n, and in the above example, the first channel TV signal is extracted from all main line amplifiers up to the terminal, and the main line In order to identify each amplifier, down converters 13-1, 13-2 to 13-
Each signal is converted into its own frequency band by n and frequency-divided. In addition, the above-mentioned band compression is performed because the video signal of the television signal is assembled from a signal with a repeating field frequency of 60 Hz and a scanning frequency of 15,750 Hz, so the bandwidth is 4.5 M)
Based on the fact that necessary signals within the video frequency band width of Hz exist with a predetermined frequency interval, unnecessary signals between these necessary signals are removed and the necessary band is narrowed.
It is possible to maintain sufficient signal quality by compressing the bandwidth including the audio signal to about 2 MHz.

By compressing the frequency range of the TV signal, the total number of monitoring TV signals that can be reversely transmitted through the auxiliary transmission line within a constant frequency band can be increased, making it possible to identify multiple main line amplifiers without worrying about mutual interference or heat. Therefore, a large number of individual bands of surveillance television signals can be transmitted back to the surveillance and reception device 6.
The monitoring/receiving device 6 is provided with a band expander 15 for restoring the band-compressed reverse transmission television signal to its original bandwidth, and the output of this expander 15 is transmitted to the down converters 13-1 and 13, respectively. The signal is input to level determiners 16-.1, 16-2 to 16-n equipped with band-pass filters having pass frequency bands corresponding to the output frequency bands of -2 to 13-n.

Each of the level determiners 16-1, 16-2 to 16-n has an indicator 17-1, 17-2 to 17-n at its output end, and each of the main line amplifiers 4-1, 4-2 -4-n is provided.

That is, the level determiner 16-1 converts the branched output of the main line amplifier 4-1 into a band pass filter 11-1, a down converter 13-1, a band compressor 14-1 and a band expander 1.
5 and operates the indicator 17-1 when the level is below a predetermined level, and the level determiner 16-2 outputs the branched output of the main amplifier 4-2 to the band-pass filter 11-2.
, the down converter 13-2, the band compressor 14-2, and the band expander 15, and when the received signal is below a predetermined level, the display 17-2 is activated, and each level determiner 16 is operated in the same manner. -1, 16-2 to 16-n detect a drop in the level of the branch output of the corresponding main amplifier. The output of the band expander 15 is also frequency-switched by the up converter 18 corresponding to each output frequency band of each down converter into, for example, a positive band air channel or several channels of the UHF band, and this is input to the monitor television receiver 9. Any reversely transmitted television signal can be viewed as an image, and of course only the output of the up-converter 18 may be received by a separate monitor television receiver. In this invention, a unique frequency band is assigned to each trunk amplifier, and the output television signal of an arbitrary broadcasting channel is extracted from each trunk amplifier, and the output television signal is transferred to the unique frequency band. After converting each, it is returned to the head end via an auxiliary transmission line, and each main line amplifier is separated into multiple units by a level judge and display set corresponding to each of the above unique frequency bands and a monitor TV receiver. It is possible to monitor faults in the main line system in a section while viewing the actual images. Therefore, according to the present invention, even if the number of broadcast channels is small, it is possible to effectively identify and monitor main line amplifiers with more channels, and even in the largest transmission system, the auxiliary transmission line as a monitoring line can be used as a monitoring line. Since a signal converted to a lower frequency than the extracted TV signal is transmitted, not only is there a transmission loss, but when it is received by the monitor TV receiver in the monitoring receiving device, the TV signal from the head end may be a direct wave. Since no interference occurs, no ghost occurs, and the quality of the monitoring image can be maintained favorably.

In the above-mentioned embodiment, the surveillance television signal is reversely transmitted to the surveillance receiver as an electrical signal, but it is possible to use an optical cable as the auxiliary transmission line to convert the surveillance television signal into an optical signal and reversely transmit it with low loss. You may also do so.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a CATV system according to an embodiment of the present invention. 3: Transmission trunk line, 4-1, 4-2 to 4-n: Trunk line amplifier,
6: Monitoring receiver, 9: Monitor television receiver, 10:
Auxiliary transmission line, 11-1, 11-2 to 11-n: band pass filter, 12-1, 12-2 to 12-n: signal sending device, 13-1, 13-2 to 13-n: down converter , 14-1, 14-2 to 14-n: band compressor, 15
: Band expander, 16-1, 16-2 to 16-n: Level determiner, 17-1, 17-2 to 17-n: Display, 18
: Up converter.

Claims (1)

[Claims] 1 Assign any specific broadcasting channel to each of the multiple main line amplifiers inserted into the transmission main line of the CATV system,
From the television signal obtained from the branch output of the trunk amplifier, only the television signal of a specific broadcasting channel assigned to the trunk amplifier is extracted, and this extracted television signal is transmitted to a TV signal unique to the trunk amplifier. A signal transmission device that converts and outputs a monitoring television signal in a low frequency band is provided near each main line amplifier, and a separate auxiliary transmission line is laid in parallel with the transmission main line, and the signal is transmitted through the auxiliary transmission line. The monitoring television signals output from each signal transmitting device are reversely transmitted, and the reversely transmitted monitoring television signals from each signal transmitting device are received to determine the output status of each main line amplifier. A centralized monitoring device for a CATV system, characterized in that a monitoring/receiving device for identifying and monitoring is provided on the head end side of the transmission trunk.