JPH0716178B2 - Communication line signal branching device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is used as a device for branching a communication signal bidirectionally transmitted over a two-wire communication line.

The present invention branches a communication signal coming from the far end and the near end to the communication line near the terminal of the two-wire communication line, and extracts the communication signal.
Suitable for use in monitoring or testing.

Here, the terminal includes a telephone terminal that transmits and receives a voice signal, or a terminal that transmits and receives an image signal or various digital signals such as a facsimile signal.

[Conventional technology]

When testing or adjusting the terminal connected to the subscriber line, actually transmit and receive communication signals between the terminal and the other terminal connected to the far end via the subscriber line and the communication network. It is sometimes necessary to monitor the communication signal by branching. FIG. 3 is a block diagram showing a conventional device for this purpose.

In FIG. 3, the terminal A is a terminal connected to the far end via the communication network NW, and the branching device EQ is inserted into the two-line subscriber line to which the terminal B at the near end is connected to The signal coming from the terminal A and the signal from the terminal B at the near end are branched and taken out to the output terminal O. Generally, the signal from the terminal A at the far end is a low-level signal that has been attenuated in the communication network, and the signal from the terminal B at the near-end is a high-level signal that has not been attenuated. Therefore, if the signals from both terminals are branched by a simple three-branch circuit, the level of the signal from the terminal B at the near end is too large to properly monitor. Therefore, as shown in FIG. 3, a variable resistance attenuator ATT is inserted between the terminal T on the terminal side and the branch point to attenuate the signal level from the terminal B at the near end. Third
In the figure, IF ₁ and IF ₂ are interfaces, and when a direct current is superposed on a communication line like a subscriber line, a direct current bypass circuit is provided as shown by a broken line DC.

[Problems to be solved by the invention]

In the above-mentioned conventional circuit, since the variable resistance attenuator ATT is used, the signal at the output terminal O, which is a branched output, can be made uniform for the signals from both terminals, but the communication signal between both terminals AB is also simultaneously affected by this variable resistance attenuation. It will be attenuated at the vessel ATT. For this reason, the level of the communication signal between the two terminals becomes different from the normal communication state, and there is a drawback that proper monitoring cannot be performed.

When the terminal B has the function of adjusting the transmission signal level, the variable resistance attenuator ATT is set to zero so that the signal level of the terminal B is adjusted to a low level equivalent to the signal level of the terminal A. However, in this case, even if the reception level of the terminal B is a normal level, the reception level of the terminal A becomes an extremely low level, and similarly it is possible to monitor an appropriate communication state. become unable.

The present invention is to improve this, and even if a signal branching device is inserted in a communication line, it does not affect the mutual communication between both terminals passing through the communication line, and the branching signal is It is an object of the present invention to provide a device capable of branching signals from terminals at substantially equal levels.

[Means for solving problems]

The present invention connects the first two-wire to four-wire conversion circuit (Ha) to the two-wire line side terminal (L) connected to the far-end terminal (A) via the communication line, and The second two-wire to four-wire conversion circuit (Hb) is connected to the two-wire terminal side terminal (T) connected to the terminal (B).
To connect the four-wire output of the first two-wire / four-wire conversion circuit to the four-wire input of the second two-wire / four-wire conversion circuit.
a) and a second signal path (Lb) that guides the four-wire output of the second two-wire to four-wire conversion circuit to the four-wire input of the first two-wire to four-wire conversion circuit.
And an amplifier (AMP) for branching and amplifying the signal in the first signal path and supplying the branched signal to the output terminal.

The first two-wire to four-wire conversion circuit is not an ideal two-wire to four-wire conversion circuit, but needs to have a characteristic of having a small signal leakage from the four-wire input to the four-wire output.

[Action]

A two-wire / four-wire conversion circuit is connected to both the line-side terminal and the terminal-side terminal, and these are connected to each other by a four-wire signal. As a result, in principle no great attenuation occurs for the mutual communication signals passing through this branching device. Regarding the branched signal, the low-level signal from the far-end terminal branches as a signal with low attenuation sent to the four-wire output of the two-wire to four-wire conversion circuit, and the high-level signal from the near-end terminal , The two-wire to four-wire conversion circuit uses the leakage from the four-wire input to the four-wire output to provide large attenuation and branch. That is, in order to attenuate the high level signal from the near-end terminal,
There is a difference from the prior art in that the leakage attenuation characteristic between the four wire terminals of the two wire to four wire conversion circuit is used.

If a two-wire to four-wire conversion circuit is configured in an ideal balanced state, the amount of leakage attenuation between two four-wire terminals will be infinite, but in general it is not possible to obtain an ideal balanced state and In the two-wire to four-wire conversion circuit for audio frequency signals, the leakage attenuation from the four-wire input to the four-wire output is about 20 dB. This is convenient because it is almost equivalent to the amount of attenuation of the signal passing through the communication network. Therefore, also for the first two-wire to four-wire conversion circuit described above, it is possible to obtain a sufficiently practical device without breaking the balance so as to intentionally cause leakage.

〔Example〕

FIG. 1 is a block diagram of the apparatus of the first embodiment of the present invention. This device includes a two-wire line side terminal L connected to a far-end terminal A via a communication line, a two-wire terminal side terminal T connected to a near-end terminal B, and a far-end terminal. And a signal from the terminal at the near end are branched and sent out, and a two-wire output terminal O is provided. A feature of the present invention is that a first two-wire to four-wire conversion circuit Ha in which two wire terminals are connected to the line side terminal L and a second two wire in which two wire terminals are connected to the terminal side terminal T are used. The four-wire conversion circuit Hb is provided, and the four-wire output 4WS of the first two-wire / four-wire conversion circuit Ha is connected to the four-wire input 4WR of the second two-wire / four-wire conversion circuit Hb by the first signal path La. Then, the four-wire output 4WS of the second two-wire to four-wire conversion circuit Hb is connected by the four-wire input 4WR of the first two-wire to four-wire conversion circuit Ha and the signal of the first signal path is connected. Is provided with an amplifier AMP for branching and amplifying and supplying it to the output terminal. Here, the first two-wire to four-wire conversion circuit Ha needs to have a characteristic of having a small signal leakage from the four-wire input to the four-wire output. In FIG. 1, BNa and BNb are balanced circuits connected to the two-wire / four-wire conversion circuit, respectively.

In this device, the signal coming from the terminal A at the far end appears at the four-wire output 4WS of the two-wire to four-wire conversion circuit Ha, and is input to the four-wire input 4WR of the two-wire to four-wire conversion circuit Hb without being attenuated. Also, the signal coming from the terminal B at the near end is a two-wire / four-wire conversion circuit.
It appears at the 4-wire output 4WS of Hb and is input to the 4-wire input 4WR of the 2-wire to 4-wire conversion circuit Ha without being attenuated. Therefore,
The attenuation of the communication signal between the terminals L and T is only the conversion loss of the two two-wire / four-wire conversion circuits Ha and Hb.

Regarding the signal branched in this state, the low level signal coming from the terminal A at the far end appears at the four-wire output 4WS of the two-wire to four-wire conversion circuit Ha, and this is not attenuated and input to the amplifier AMP. Be led to. On the other hand, terminal B at the near end
The high-level signal coming from the signal appears at the four-wire output 4WS of the two-wire / four-wire conversion circuit Hb, and is further input from the signal path Lb to the four-wire input 4WR of the two-wire / four-wire conversion circuit Ha. In the four-wire conversion circuit Ha, it undergoes a large attenuation and appears at its four-wire output 4WS, and is guided to the input of the amplifier AMP via the signal path La. That is, the signal from terminal A reaches the input of the amplifier AMP without being attenuated, and the signal from the terminal B is greatly attenuated to reach the input of the amplifier AMP. Therefore,
At the output O, the signals from both terminals have almost the same signal level.

On the other hand, assuming that the signal attenuation caused by passing through the communication network NW is about 20 dB, and the leakage attenuation from the four-wire input 4WR to the four-wire output 4WS in the two-wire to four-wire conversion circuit Ha is about 20 dB, both terminals When A and B perform transmission at the same signal level, the signal levels of both terminals appearing at the branch output terminal O become equal.

FIG. 2 is a block diagram of the apparatus of the second embodiment of the present invention. In this example, an amplifier is provided in the signal path of the four wires in consideration of the conversion loss generated in the two-wire / four-wire conversion circuit, and further, in consideration of the case where the device is directly inserted into the subscriber line for use, the DC current It is a practical device with a bypass passage.

That is, in FIG. 2, the two-wire / four-wire conversion circuits Ha and Hb
Is a two-wire to four-wire conversion circuit used for standard audio frequency signals, between the two-wire terminal and the four-wire output,
Alternatively, signal attenuation of 3.5 dB occurs between the 4-wire input and the 2-wire terminal. In order to compensate for this signal attenuation, an amplifier AMP that receives the four-wire output 4WS of the two-wire to four-wire conversion circuit Ha as an input
₁ and the output of this amplifier as input, the 2-wire to 4-wire conversion circuit Hb
An amplifier AMP ₂ having a four-wire input 4WR as an input is provided, and the gains of these two amplifiers are set to 3.5 dB, respectively. The branch point to the amplifier AMP is the connection point between the above two amplifiers AMP ₁ and AMP ₂ . Furthermore, the four-wire output of the two-wire to four-wire conversion circuit Hb
An amplifier AMP ₃ having a gain of 7 dB is connected to the signal path Lb between the 4WS and the four-wire input 4WR of the two-wire / four-wire conversion circuit Ha.

Further, since the direct current is superposed on the signals of the two wires at the terminals L and T, the direct current is prevented from being applied to the two wire to four wire conversion circuit. A direct current is shunted using a choke and a capacitor as shown and connected by a direct bypass DC so that there is a correct coupling between T and T.

In the device shown in FIG. 3, there is no signal attenuation between the line side terminal L and the terminal side terminal T. Therefore, the conditions for the communication between the terminal A and the terminal B are not changed regardless of whether or not the branching device is connected. Moreover, the low-level signal that has arrived at the terminal L from the terminal A at the far end is given to the input of the branching amplifier AMP without being attenuated. In addition, a high-level signal input from the terminal B at the near end to the terminal T is output from the four-wire output 4WS of the two-wire to four-wire conversion circuit Hb.
It reaches the four-wire input 4WR of the amplifier AMP ₃ and the two-wire to four-wire conversion circuit Ha, appears at its four-wire output 4WS after being greatly attenuated inside the two-wire to four-wire conversion circuit Ha. The leakage attenuation from the four-wire input 4WS to the four-wire output 4WR of the two-wire / four-wire conversion circuit Ha is 20 dB, and the signal attenuation received by the communication signal in the communication network NW is almost 20 dB.
Then, the signals from both terminals appear at the output terminal O at substantially equal levels. Two-wire-four-wire conversion circuit
The balanced state of Ha, that is, the leakage attenuation amount from 4-wire input 4WS to 4-wire output 4WR can be adjusted by the value of the balanced network BNa connected to this 2-wire to 4-wire conversion circuit Ha. Then, the signal levels from the two terminals A and B can be adjusted to be equal at the output terminal O.

The relationship between the signal levels will be further described in detail with reference to an example in which the transmission signal level of the terminal A is 0 dBm and the communication network NW
Loss of 11 dB to 25 dB and standard value of 18 dB. Also, the leakage attenuation between the four wire terminals of the two wire to four wire conversion circuit Ha is set to 20 dB. At this time, if the transmission signal level of the terminal B is set to -5 dBm, the transmission signal of the terminal B is 3.5d in the two-wire / four-wire conversion circuit Hb.
Receives B attenuation and is amplified by amplifier AMP ₃ by 7 dB,
The signal level of the 4-wire input 4WR of the 2-wire to 4-wire conversion circuit Ha is -1.5.
It becomes dBm. Therefore, it appears at −21.5 dBm in the four-wire output 4WS of the two-wire / four-wire conversion circuit Ha. On the other hand, the transmission signal from terminal A is input to terminal L with a standard value of -18 dBm, and the two-wire to four-wire conversion circuit H
Since it is attenuated by 3.5 dB at a, the output 4WS appears at −21.5 dBm and the signal from terminal A and the signal from terminal B have the same level.

When the attenuation amount of the communication network NW fluctuates from the standard value, the signal level from the terminal A fluctuates according to the fluctuation amount. Also, since the equilibrium state of the 2-wire to 4-wire conversion circuit Ha can be changed by the value of the connected balance network BNa, the 2-wire to 4-wire conversion circuit H
The leakage attenuation between the four wire terminals of a can be adjusted accordingly.

〔The invention's effect〕

As described above, according to the present invention, even if the signal branching device is inserted in the communication line, the level of the mutual communication signal of both terminals passing through the communication line is not affected and the signal is branched. It is possible to obtain branched outputs from both terminals so that the signals have almost equal levels.

[Brief description of drawings]

 FIG. 1 is a block diagram of the apparatus of the first embodiment of the present invention. FIG. 2 is a block diagram of the apparatus of the second embodiment of the present invention. FIG. 3 is a block diagram of a conventional device.

Claims (1)

[Claims] 1. A two-wire line side terminal (L) connected to a far-end terminal (A) through a communication line, and a two-wire terminal side terminal (L) connected to a near-end terminal (B). T)
And a signal output device (O) of two wires for branching and transmitting the signal from the far-end terminal and the signal from the near-end terminal, the line-side terminal A first two-wire to four-wire conversion circuit (Ha) in which the two-wire terminal is connected to, and a second two-wire to four-wire conversion circuit (Hb) in which the two-wire terminal is connected to the terminal side terminal, A first signal path (La) for guiding the four-wire output of the one two-wire four-wire conversion circuit to the four-wire input of the second two-wire four-wire conversion circuit.
And a second signal path (Lb) for guiding the four-wire output of the second two-wire to four-wire conversion circuit to the four-wire input of the first two-wire to four-wire conversion circuit.
And an amplifier (AMP) for branching and amplifying the signal in the first signal path and supplying the amplified signal to the output terminal. The first two-wire to four-wire conversion circuit converts the four-wire input to the four-wire output. A signal branching device for a communication line, which has a small signal leakage.