JPS6040069Y2 - Central monitoring device for CATV system - Google Patents

Description

[Detailed explanation of the invention] The transmission trunk line in the dendritic wiring CATV system is
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 amplifiers are inserted in the middle, and four or more branch transmission lines are separated from each main amplifier.
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. This required a large number of elements, and a stable monitoring operation could not be expected.

This device effectively utilizes the TV signal of a broadcast channel as a monitoring signal to enable monitoring with actual images, and also enables monitoring failures to be displayed without malfunctioning even after broadcast waves have stopped, such as at night. A CATV system that allows monitoring signals to be identified for each section of a transmission trunk divided into multiple trunk expansion types even if the number of channels is small, making it easy to understand the location of failure and the extent of the failure. The aim is to obtain a centralized monitoring device for

Next, this invention will be explained with reference to the drawings showing an embodiment of the invention. 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 pressures.

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
indicator 8-1.8- correspondingly activated by the output of
2 to 8-7 are provided to monitor the output status of each broadcast channel of the head end 2.

Incidentally, a monitor television receiver 9 connected to the output side of the head end 2 is also provided in the monitoring and receiving apparatus, so that the head end 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 1-n is placed in its vicinity.
and a down converter 13.
are provided, and other intermediate main line amplifiers 4-1 to 4-n-1
For each bandpass filter 11-
1 to 1l-n-1 and level determination devices 14-1 to 14-
Signal transmitting devices 12-1 to 12-n-1 are provided, each of which includes a switching device 15-1 to 15-n-1, and an oscillator 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, with a channel bandwidth of 6 MHz, and the down converter 13 extracts this extracted specific broadcasting signal. The television signal of the channel is frequency-converted to a monitoring television signal of a lower frequency while maintaining its band, and is output to the auxiliary transmission line 10 and reversely transmitted to the monitoring reception 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 13 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 single frequency signal such as a video signal carrier wave of a television signal of an arbitrary broadcasting channel is extracted from the branch outputs of 2 to 4-n-1 in a narrow band, and this narrow band signal is passed to the level determination device 1.
4-1.14-2 to 14-n-1.

Each of the level determination devices 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 determines whether or not an input of a predetermined level or higher is given. Switching device 15-1.15-
2 to 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 transmitter 12-n. The terminal signal sending device 12-n
Monitoring television signals from and intermediate signal transmitting devices 12-
Each of the monitoring signals from 1.12-2 to 12-n-1 is frequency-divided and reversely transmitted to the monitoring receiving device 6 via the auxiliary transmission line 10.

In this case, the frequency allocation of each oscillator should be set 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 is determined to be the lowest. advantageous in terms of

Within the monitoring and receiving device 6, there is a detection device 17-1 that 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 to 17-n,
Monitoring display devices 18-1, 18-2 to 18-n are activated in response to the respective outputs of the detection device, and an up-converter takes out the monitoring television signal from the auxiliary transmission line 10 and returns it to the original frequency band. 19 and the up converter 1
There is further provided another monitor television receiver 20 for receiving the specific broadcast channel extracted as the monitoring television signal by the output of the monitor 9.

In other words, each signal sending device 12-1.1 during normal operation.
Each monitoring signal and each monitoring television signal from 2-2 to 12-n are detected by a corresponding detection device 17-1, 17-2 to 1, respectively.
7-n, and therefore each display device 18-1, 18-2 to 1
8-0 remains inactive.

The monitoring television signal from the terminal signal transmission device 12-n or the up-converter 19 returns the frequency band of the original specific broadcast channel to another monitor television receiver 20.
An image is received.

When the level of the branch output of any main line amplifier drops due to a disconnection or main line amplifier failure, 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 transmission device drops drastically or is interrupted.
Accordingly, all the corresponding rear-stage displays 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 fault or a main line amplifier failure causes the output of the signal sending device downstream of the fault point to be cut off, causing the corresponding detection device to generate an output and display the indicators 18-1 to 18.
−It activates the corresponding one among the circles.

This fault display operation is performed when broadcast waves are present,
When there is no broadcast wave, the display 18
-1 to 18-n and headend monitoring display 8-1
~8-7 all work.

In this invention, in order to prevent this, a pseudo signal sending device 21 is further provided in the head end 2 as shown in FIG.

That is, FIG. 2 is a block diagram showing the detailed configuration of the second head end of the CATV system according to the second invention, which includes a branching filter 22 that branches the received wave from the antenna 1 for each broadcast channel, and the branching filter 22. Amplifiers 23-1 to 2 for each broadcast channel that amplify each channel wave to a predetermined level.
3-7 (7 channels in the illustrated example) and a mixer 24 that mixes the outputs of each amplifier and outputs the mixture to the transmission trunk line 3.
is attached.

This pseudo signal sending device 21 is connected to each of the amplifiers 23-1 to 23-2.
Level detection device M25- consists of a detection amplification/switching element that receives each output of 3-7 and determines its level.
1 to 25-7 and each level detection device 25-1 to 25-7
When the output of each amplifier 23-1 to 23-7 falls below a predetermined level, the relay contact 26a
- Relay device 26-1 to close each of 1 to 26a-7
26-7 and the above 1) (7-Amplifiers 23-1 to 23-7 provided corresponding to each of the contacts and having the same frequency as the television signal of the broadcast channel served by, for example, a video signal carrier wave or fixed It is provided with signal generators 28-1 to 28-7 that generate pattern video signals and the like based on the energization of the power supply 27 by closing the relay contacts and send them to the transmission main line 3.

Specifically, the signal generators 28-1 to 28-7 are sequentially assigned to each broadcasting channel, for example, the signal generator 28-1 is assigned to the first channel, the signal generator 28-2 is assigned to the third channel, and so on. Then, the signal generator 28-7 generates a pseudo signal having the same frequency as the video signal carrier wave of the broadcast wave of the 12th channel, and also generates a signal corresponding to the television signal extracted by the terminal signal transmitter 12-n, for example. Only the generator 28-1 may be a fixed pattern generator that generates a fixed pattern video signal with a predetermined bandwidth that provides a fixed image.

With this configuration of the headend 2, even if the broadcast waves stop on some or all channels, such as at night, the pseudo signal will automatically replace the transmission main line for the channels where the broadcast waves have stopped. As a result, the above-mentioned failure monitoring of the main line system can be effectively performed even when broadcast waves are interrupted, and the head-end monitoring displays 8-1 to 8-7 are also activated when broadcast waves are interrupted. This will prevent you from doing so.

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. In the case where there is air discharge from a main line amplifier in a main line, a narrowband 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.

FIG. 3 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 7 channels, 10th and 12th channels, and 7 main line amplifiers.

In FIG. 3, the head end 2 is assumed to have the configuration shown in FIG. Signal sending device 1 consisting of a narrowband bandpass filter (or tuner) 11'-1 for extracting this
A narrow band pass filter (or Tuner) Signal sending device 1 consisting of 11'-2
2'-2, and in the same manner, a signal transmitting device 12'- consisting of a bandpass filter 11'-7 that extracts the television signal of the first channel only to the main line amplifier 4-7 at the end. 7 is provided.

That is, from the terminal signal transmitting device 12'-7, the television signal itself of the first channel is reversely transmitted as a monitoring television signal to the monitoring receiving device 6 via the auxiliary transmission line 10.
Other signal sending devices 12'-1, 12'-2...
From there, the video signal carrier waves of the 12th channel, the 10th channel, and so on are reversely transmitted to the monitoring and receiving device 6 via the auxiliary transmission line 10 as narrowband broadcast monitoring signals.

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 level determiners 17'-1, 17'-2, . . . with band-pass filters.
The level of the monitoring television signal alone was determined by the final stage level determiner 17'-7, and the frequency was converted to one of the empty channels or VHF channels via the converter 29. Then, it is input to the monitor television receiver 9.

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

As mentioned above, according to this invention, the TV signal of the broadcast channel is returned only from the main line amplifier at the end for image monitoring, so the TV signal of any broadcast channel is returned from the other intermediate main line amplifiers. It is only necessary to return the monitoring signal whose signal content is only level judgment, and therefore, these monitoring signals do not require a wide range, so a large number of monitoring signals can be handled within a certain frequency band, and broadcasting at night etc. Failure monitoring is possible without malfunctioning of the display 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 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 an embodiment of this invention, FIG. 2 is a block diagram showing a detailed configuration example of its head end, and FIG. 3 is the same (another embodiment of the CATV system). It is a block diagram showing 3...Transmission main line, 4-1.4-2 to 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
B-1, 18-2 to 18-n... Indicator, 19
......up converter, 20...monitor television receiver, 21...pseudo signal sending device, 25-1 to 25-7...level detection device, 2
6-1 to 26-7... Relay device, 27...
...Power supply, 28-1 to 28-7...Signal generator.

Claims (1)

[Scope of utility model registration request] An arbitrary specific broadcasting channel is assigned to each of a plurality of main line amplifiers inserted into the transmission main line of a CATV system, and the TV signals obtained from the branch outputs of the main line amplifiers are allocated to the main line 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 unique signals from each signal sending device are reversely transmitted via the auxiliary transmission line, and the transmitted unique signals are received from the auxiliary transmission line. A monitoring/receiving device for identifying and monitoring the output status of each main line amplifier based on their own frequencies is provided on the head end side of the transmission main line, and further within the head end device connected to the front of the transmission main line, A centralized monitoring device for a CATV system, characterized in that it is provided with a pseudo signal sending device that oscillates pseudo signals of the same frequency as the received waves of the stopped broadcast channel when the broadcast waves stop, and sends them to the transmission main line. .