JPH0964794A - Modulator/demodulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an exact loop back test by detecting the level difference of the reception level from an opposite station and the transmission level of a present station, controlling the gain of a loop back amplifier by this detection signal and always performing a loop back by a constant transmission level. SOLUTION: This device has a switching device 3 normally selecting the present station transmission signal from a transmission level setting part 2 and selecting a loop back signal when a switch signal instructing the loop back from an opposite station is received by a demodulation part 4, an amplifier 7 for gain variable loop back for compensating the line loss on a line side and a reception level detection circuit 6 detecting the level of a reception line signal, and the device is provided with a loop back level control part 5 comparing the detection value of a reception level and the set value of a transmission level and performing a gain control for the amplifier for loop back by the difference signal. The reception line signal is automatically amplified to a constant loop back level and the loop back is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a modem for data transmission, and more particularly to a modem using an analog 4-wire dedicated line and having a loopback test function.

[0002]

2. Description of the Related Art Conventionally, this type of modulation / demodulation apparatus has a loopback function on the line side, that is, an analog loopback (ALB) function, as one of test functions. The ALB function is a function of returning the receiving line signal on the line side to the transmitting side.
This is for performing a transmission / reception test later.

In other words, the ALB is executed by receiving the ALB instruction signal from the other modem and returning the received line signal to the transmitting side. At this time, the received line signal reflects the line loss by the return amplifier. It is compensated and folded at the same level as the transmission level of the transmission line signal.

For example, as disclosed in Japanese Patent Application Laid-Open No. 62-72237, a folded receiving line signal is amplified by a folding amplifier set in advance to a gain for amplifying a line loss, and is then folded back to a transmission line. . However, when the reception level exceeds the standard, an accurate test cannot be performed. At this time, there is a function to prohibit ALB. See also Sho 63-1204
In Japanese Patent Publication No. 42, the reception level before ALB switching is latched, the gain of the folding amplifier is set with the retained level, and the reception level is increased and folded by the folding amplifier.

[0005]

As described above, in the conventional example, since the gain of the loop-back amplifier is set in advance or the gain is set at the reception level immediately before the loop-back, an accurate loop-back is performed at that time. The transmission level is set. Thereafter, particularly, the fluctuation of the reception level during the loopback becomes the fluctuation of the loopback transmission level as it is. In such a case, there is a problem that an accurate loopback test cannot be performed.

[0006]

According to the present invention, there is provided a modem apparatus comprising:
A modulation unit that converts a transmission data signal from a terminal into a line-side analog transmission line signal, a transmission level setting unit that sets a transmission level of the transmission line signal from the modulation unit, and always transmits the transmission line signal. A switch that transmits to the transmission line side and switches a return line signal for return by the switching signal to the transmission line side, and a switch that amplifies the reception line signal on the reception line side and performs the switching as the return reception line signal; A variable gain type folding amplifier to be added to the amplifier, the level of the reception line signal is detected, the detected level is compared with the transmission level of the transmission level setting section, and the gain of the folding amplifier is calculated by a difference signal indicating the level difference. A return level control unit for controlling the reception line signal into a reception data signal on the terminal side, and at the same time, a signal from the other modem included in the reception line signal. And a demodulator for detecting the switching signal and outputs it to the switch.

[0007]

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

FIG. 1 is a block diagram showing a configuration of an embodiment of the present invention. The modulation and demodulation apparatus converts a transmission data signal from a terminal into an analog transmission line signal on a 4-wire dedicated line, and converts a reception line signal received from the 4-wire dedicated line into reception data on the terminal. And a receiving side for demodulating the signal.

On the transmitting side, a modulation section 1 for modulating a transmission data signal from a terminal side, and a transmission level setting section 2 for adjusting a modulated transmission line signal to a predetermined level.
And a switching device 3 for switching and transmitting the transmission signal and the return signal of the own station.

On the receiving side, a demodulation unit 4 receives a receiving line signal from the line side, modulates the signal into a receiving data signal on the terminal side, and simultaneously detects a switching signal inserted into the receiving line signal; A reception level detection circuit 6 for measuring the level, a return level control unit 5 for controlling the return level based on the detected value of the reception level and the set level of the transmission level setting unit 2, and a gain control by the return level control unit 5; Return amplifier 7 for compensating for line loss
With.

Next, the operation will be described. The switch 3 always selects the own station transmission signal from the transmission level setting unit 2 and sends it to the line side as a transmission line signal. When the switching signal from the partner station inserted into the reception line signal is detected by the demodulation unit 4, the switching signal is input to the switch 3. As a result, the switch performs a switching operation and sends a return signal to the line side instead of the own-station transmission signal, thereby forming an ALB.

The level of the reception line signal is detected by a reception level detection circuit 6, and this detection signal is input to a return level control section 5. The detection signal is transmitted by the transmission level setting unit 2
And a difference signal indicating the level difference is extracted and applied to the gain control circuit of the folding amplifier 7.

The return amplifier 7 receives the reception line signal, amplifies the signal by the line loss, that is, the difference signal of the return level control unit 5, and inputs the amplified signal to the switch 3 as the return signal. The transmission level set by the transmission level setting unit 2 keeps a constant value, but the reception line signal fluctuates due to the fluctuation of the line loss. The folding amplifier automatically adjusts the fluctuation of the reception level to increase the reception line signal to a constant folding transmission level.

[0014]

As described above, the modulation / demodulation device of the present invention detects the reception level, and automatically controls the gain of the folding amplifier based on the level difference between the detected value and the set value of the transmission level. Therefore, a constant return transmission level can always be maintained without being affected by fluctuations in the line loss. Therefore, there is an effect that an accurate loopback test can always be performed.

[Brief description of drawings]

FIG. 1 is a block diagram showing an exemplary embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Modulation part 2 Transmission level setting part 3 Switcher 4 Demodulation part 5 Return level control part 6 Reception level detection circuit 7 Return amplifier

Claims (1)

[Claims] A modulator configured to convert a transmission data signal from a terminal into an analog transmission line signal on a line side; a transmission level setting unit configured to set a transmission level of the transmission line signal from the modulator; A switch for transmitting the transmission line signal to the transmission line side and switching and transmitting a reception line signal for return to the transmission line side by a switching signal; and amplifying the reception line signal on the reception line side for receiving the return signal. A variable gain type folding amplifier to be added to the switch as a line signal,
A folding level control unit that detects the level of the reception line signal, compares the detection level with the transmission level of the transmission level setting unit, and controls the gain of the folding amplifier with a differential signal indicating this level difference; A modulator / demodulator that converts a signal into a reception data signal on the terminal side and, at the same time, detects the switching signal from the counterpart modulation / demodulation device included in the reception line signal and outputs the switching signal to the switch.