JPS6173436A - Bidirectional repeating amplifier - Google Patents

Abstract

PURPOSE:To omit a low group pilot signal rejector and a pilot signal transmitter on the terminal side by providing a high group pilot signal detector to a high group signal input part of a bidirectional repeating amplifier. CONSTITUTION:The high group pilot signal detector 18 extracts only a pilot signal for AGC out of high group signals SH obtained from a center head end, and outputs a detected output proportional to the receiving level to an AGC driving circuit 19 as a signal S18. The circuit 19 sends a driving signal S19 corresponding to the signal S18 to a low group AGC driving circuit 20. The circuit 20 executes the automatic gain control of a low group signal SL obtained from a low group signal amplifier 17 on the basis of the signal S19 and outputs the gain-controlled low group signal SL to an I/O terminal 12 through another low group signal amplifier 21 and a high group/low group distributor 13. Thus, the AGC of the low group signal SL can be attained by always detecting the level of the high group pilot signal, converting the detected level into a low group variable and supplying the variable to the circuit 20.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a bidirectional repeater amplifier (=== used in a CATV (Cable Ten Vision) system (==== equipped with an AGC (Automatic Gain Control) function).

[Conventional technology]

Figure 2 shows a conventional C
1 shows an example of the configuration of an ATV system. The center head end 1 includes transmitters 2 and 6 that transmit television signals and pilot signals, respectively, receives a low group signal SL sent from the terminal side, and receives the low group signal SL.
The high group signal (TV signal and pilot signal) SK1 to be transmitted is input, and only the low group signal SL is demultiplexed and sent to the receiver 4 (:, the high group signal SL is combined with an appropriate control signal to receive the high group signal SN). It has a built-in demultiplexing coupler 5 that sends out two transmission lines 6A and 6A.These six transmission lines are branched into transmission lines 6B and 6C (; -6 transmission lines 6B and 6C) by a trunk distributor 7.
A C1 two-way repeater amplifier 8A r 8B is provided, and the two-way repeater amplifiers 8A and 3B further connect the transmission line 6.
D and 6E, 6F and 6G (= branched to each terminal 10A, 10
B, 10C and 10D (- connected. Each terminal 1
Similar to the center head end 1, 0A to 100 have a function of transmitting a pilot (g) in addition to a transmission signal as information, that is, a pilot signal transmission a11A to 11.
It has D.・Also, bidirectional relay amplifier 8A,
8B+= is equipped with low group pilot signal removers 9A and 9B (described later).

Note that although the configuration shown in Figure #42 is shown schematically to simplify the explanation, in reality, the transmission path is configured in a more complicated dendritic manner.

The two-way relay amplifiers 8A and 8B used in the system configured as described above each transmit a high group signal Sm from the center head end 1 to each of the terminals 10A to 10D.
The low group signal SLc from each terminal 10A to 10D toward the center head end 1 is detected from the center head end 1 for the two terminals. However, based on the signal level and frequency, the pylon AGC method was used to automatically compensate for cable loss that fluctuates due to ambient temperature C2.

[Problems to be Solved by the Invention] The CATV system has a two-dendritic transmission path configuration (as shown in FIG. 2). In such a configuration, when considering a low group line from the end of the transmission path, that is, from each terminal 10A to 10D to one recenter head end, the low group pilot signal is transmitted from the pilot signal transmitter 11A of each terminal 10A to 100.
11D, the low group pilot signal becomes multiple waves at the branching/joining points of the transmission line, that is, the bidirectional repeating amplifiers 8A and 3Bl2, causing a beat disturbance. For this reason, the aforementioned low group pilot signal removers 9A and 9B, which pass only one pilot signal and remove the other pilot signals, are connected to the bidirectional relay amplifiers 8A and 8.
It is provided in B. Therefore, there are disadvantages in that the transmission characteristics deteriorate and, furthermore, the provision of such a wave remover leads to a decrease in economic efficiency.

An object of the present invention is to provide a bidirectional repeater amplifier that eliminates the need for a low-group pilot signal remover and a pilot signal transmitter on the terminal side, and enables construction of an economical CATV system without deteriorating transmission characteristics. There is a particular thing.

[Means for solving problems]

In order to achieve the above object, the present invention provides a high group pilot that detects a pilot signal included in this high group signal and outputs a detection signal according to its level to a high group signal input section of a bidirectional relay amplifier. A signal detector is provided, and the gain of the low group signal (not including the pilot signal) input from the low group signal input section is automatically controlled based on the detected signal.

It is known that the change in loss due to the ambient temperature of a CATV cable is approximately proportional to the square root of the signal frequency. Therefore, the level of the signal input to the high group pilot signal detector is changes according to cable loss fluctuations, so by detecting the level and frequency of this signal, the cable loss on the low group side, in other words, the signal level that should be used on the low group side can be determined.

In other words, the bidirectional relay amplifier according to the present invention (:
a high group pilot signal detector that extracts only the included pilot signals and outputs a detection signal according to its level;
Based on this detection signal, the control section automatically controls the gain of the low group signal not including the pilot signal inputted from the other terminal and sends it to the one terminal described above.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic block diagram showing one embodiment of a bidirectional relay amplifier according to the present invention. The input/output terminal 12 receives a high group signal S transmitted from a center head end (not shown).
This is a terminal for inputting signal R and outputting a low group signal SC transmitted from a terminal (not shown) toward the center head end. The high group and low group demultiplexer 16 has an input/output terminal 12
The high group signal axis inputted through It is sent to a group signal amplifier 14 and a group pilot signal detector 18. The bacterial swarm signal SR amplified by the high swarm signal amplifier 14 is sent to the input/output terminal 16 via the high/low group demultiplexer 15 . Similar to the input/output terminal 12 described above, this input/output terminal 16 inputs the low group signal St transmitted from the terminal, and also inputs the high group signal S) I transmitted from the center helmet end in the terminal direction. This is a terminal for outputting to. Similarly to the above-mentioned high group and low group demultiplexer 16, the 14 group low group demultiplexer 15 also receives the low group signal St input via the input/output terminal 16 and the high group signal St sent from the center head end. The group signal SR is demultiplexed, the high group signal S is sent to the input/output terminal 16, and the low group signal SL is sent to the low group signal amplifier 17.

On the other hand, the high group pilot signal detector 18 extracts only the pilot signal for AGC from the high group signal S8 transmitted from the center head end, and extracts the AGC pilot signal as a detection output signal 5li1 proportional to the reception level (-). circuit 19
Strengthen. The AGC drive circuit 19 sends the drive signal S1 to the low group AGC circuit 20 in response to this signal 811. The low group AGC circuit 20 uses the drive signal srs of the AGC drive circuit 19 to drive the low group signal amplifier 1 as described above.
AGC is performed on the low group signal SL from 7, and the AGCed low group signal S1 is outputted to the input/output terminal 12 via another low group signal amplifier 21, high group low group splitter 16, Ru.

Note that the high group signal S includes a pilot signal for high group AGC, but the low group signal SL does not include a pilot signal for low group AGC. Further, since it is not directly related to the gist of the present invention, the AGC circuit for high group signals has been omitted.

Next, the AGC of the bidirectional relay amplifier configured in this way will be explained.
I will explain about it.

First, the high signal island transmitted from the center head end (not shown) is input/output terminal 12. The signal is inputted to the high group signal amplifier 14 through the high group and low group demultiplexer 16 and is also inputted to the high group pilot signal detector 18 . The high group pilot signal detector 18 extracts only the pilot signal from the high group signal islands, and obtains a detection output Sll corresponding to its reception input level (:). This output Sta is the AGC drive circuit 1
9 and is manually input to the low group AGC circuit 20.

Now, let us consider a case where cable loss fluctuates due to changes in ambient temperature. According to the above-mentioned Kyoto theory, the change characteristics (frequency, wave number characteristics) of CATV A cable loss due to temperature (=
It is known that it is proportional to the square root of the frequency.

That is, since the level of the high group pilot signal is received while changing in accordance with the cable loss fluctuation, the amount of variation in cable loss at the pilot frequency can be determined by detecting the level of the high group pilot signal. Therefore, the received signal level at high group pilot frequencies causes low n
Since the amount of cable loss change at I can do it.

〔Effect of the invention〕

As explained above, the present invention provides AGC of the low group signal St.
Since the circuit configuration uses the high group signal Sn, a pilot signal transmitter at the terminal is not required,
As a result, there is no need for a low group pilot signal remover that inserts C2 to remove beat disturbances due to overlap of low group pilots (m number) at the branching/coupling points of the transmission path.Therefore,
Economical bidirectional CAT without deteriorating transmission characteristics
V system can be constructed.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram showing an embodiment of a bidirectional repeating amplifier according to the present invention, and FIG. 2 is a diagram showing an example of the configuration of a CATV system using a conventional bidirectional repeating amplifier. 1...Center head end. 2...TV signal transmitter. 6... (High group pilot signal transmitter. 4... Receiver, 5... Demultiplexing coupler. 6A to 6G... Transmission line, 7... Trunk distributor. 8A, 8B. ...Bidirectional relay amplifier. 9A, 9B... (low group) pilot signal remover. 10A to 100... terminal. 11A to 11D... (low group) pilot signal transmitter. 12.16. - Input/output terminal. 13.15... High group low group splitter. 14... High group signal amplifier. 17.21... Low group signal amplifier. 18... High group pilot signal detector. 19...AGC drive circuit, 20...Low group AGC circuit. SR...High group signal, sL...Low group signal. S, Hatake+SI嘗...Each signal.

Claims (1)

[Claims] A high group pilot signal detector that extracts only the pilot signal included in the high group signal from among the high group signals inputted from one terminal and outputs a detection signal according to the level thereof. , a control section that automatically controls the gain of a low group signal that does not include a pilot signal that is input from the other terminal based on the detection signal and sends it to the one terminal. .