JPS62173825A - Testing system for modulator demodulator - Google Patents

Abstract

PURPOSE:To loop back the transmission level of line standards even if secular change occurs in the line characteristic, by setting an amplification gain value, which compensates the difference between the measured value of a reception signal level and a reference transmission level, to an amplifying circuit in a back loop. CONSTITUTION:When the looping command from a modulating and demodulating device 2 passes a communication line 4 and is demodulated by a demodulating circuit 6 and is outputted as reception data 21, a control circuit 11 reads an output 22 from a level measuring circuit 10 which measures the reception signal. The gain of the amplifier 9 is controlled by a control signal 23 so that the output level of an output signal 25 of the amplifier 9 is 0dBm, and a control signal 24 is outputted to switch circuits 12 and 13 so that they are in contact states to form a loop. Thus, a transmission signal is transmitted in the loop-back transmission level in circuit standards even if the line loss characteristic is varied by secular change.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a test method for testing a modem, and more particularly to a method for setting a return output level when forming an analog loop.

[Conventional technology]

Conventionally, when forming an analog loop in which a received signal is folded back as a transmitted signal in response to a command from a remote modem in a data modem, the gain of the next amplifier installed in the analog loop to compensate for line loss is As a result, the received signal was amplified by the amplification gain of the ratio value set when the modulator/demodulator tl was installed and adjusted, and the received signal was returned and transmitted.

[Problem that the invention seeks to solve]

In the conventional method described above, even if the line loss fluctuates over time and the loss differs from the loss at the time of installation and adjustment of the modulator/demodulator, the received signal is reduced by the amplification gain set in the amplifier. This method has the disadvantage that it may be amplified and sent back, which may cause it to deviate from the line standard.

[Means for solving problems]

In order to solve these drawbacks, the modem test method of the present invention includes a switch circuit that forms an analog loop that loops the received signal back to the line side and a gain value that can be switched and set using a control signal in the data modem. An amplifier installed in the analog loop, a level measurement circuit that measures the received input signal level, and a command indicating an analog loop command from a remote modulation/demodulation device via the main channel are decoded, and the output of the level measurement circuit is The control circuit includes a control circuit that reads and outputs a control signal to the amplifier to operate the switch circuit, and reads the output of the level measurement circuit when receiving a command indicating an analog loop command from the remote modem device. Accordingly, the present invention is characterized by having a procedure of operating the switch circuit to form an analog loop after setting the gain value of the amplifier so that the folded output level does not exceed a predetermined value.

[For production]

According to the present invention, when a command to instruct an analog loop from a remote modem is received, an amplification gain value that guarantees the difference between a received signal level measurement value and a reference transmission level is applied to an amplifier in the analog loop. It becomes possible to set.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

The figure is a block diagram showing an embodiment of a modem test method according to the present invention. In the figure, 1 is a data modem and 2 is a remote modem, and these modems 1 and 2 are connected via communication lines 3 and 4. The modulation/demodulation device 1 includes a modulation circuit 5 for modulating transmission data, a variable resistance attenuator 7 for adjusting the level of the modulated analog signal, and a communication line 4.
A demodulation circuit 6 is provided which demodulates the received signal from the modulation/demodulation device 2 through the demodulation device 2 and outputs received data 21 . moreover,
Switch circuits 12 and 13 that form a companion analog loopback for looping back the received signal on the line side, and an amplifier configured between the switch circuits 12 and 13, whose amplification gain value can be variably set by a control signal to be described later. 9 and
A level measuring circuit 10 that measures and outputs the received signal input level; and a main channel that decodes commands indicating analog loop commands from the modulator/demodulator 2 and reads the output of the level measuring circuit 10, and controls the amplifier 9; A control circuit 11 is provided which outputs a signal and operates switch circuits 12 and 13. Here, when a certain predetermined signal bang is detected from the received data 21 of the control circuit 11Yi, it is regarded as an analog loop bank command, and the output 22 of the level measuring circuit 10 is read. A switch circuit 1 outputs a control signal 23 for setting the gain to the amplifier 9 and forms an analog loopback.
A series of procedures for outputting the switching control signal 24 to the terminals 2 and 13 are executed.

Next, in the configuration of the above embodiment, the operation when the modem 1 forms an analog loop based on a command transmitted from the remote modem 2 will be described. In the modem 1, when an analog loop command is not received, the switch circuits 12 and 13 are in a contact state that does not form the loop, and the level measuring circuit 10 is assumed to continuously measure the level. . When the analog loop command from the modulation/demodulation device 2 is demodulated by the demodulation circuit 6 via the communication circuit +W4 and outputted as received data 21, the control circuit 11 controls the level measurement circuit 11 which is measuring the received signal input. Read the output 22 of Then, the output level of the output signal 25 of the amplifier 9 is 0 dBrrt.
The gain of the amplifier 9 is controlled by the control signal 23 so that the following occurs, and the control signal 24 is output to the switch circuits 12 and 13 so that the contact state forms an analog loop. Therefore, by the above-described operation, it is possible to form an analog loop in the modem 1 based on the command from the remote modem 2.

〔Effect of the invention〕

As explained above, the present invention provides an amplification gain value that guarantees the difference between the received signal level measurement value and the reference transmission level when receiving a command to instruct analog looseness from a remote modem. The advantage of this setting is that even if the line loss characteristics change over time, the transmission signal can be sent out at the tick-back transmission level within the line standard.

[Brief explanation of drawings]

The drawing is a block diagram showing one embodiment of the present invention. 1.2...modulation/demodulation device, 3,4...communication circuit,
5φ...Modulation circuit, 6...Demodulation circuit, T...
Variable resistance attenuator, 9...Amplifier, 10...Level measurement circuit, 11...Control circuit, 12.13...
・Switch circuit.

Claims (1)

[Claims] In a data modulation/demodulation device, there is a switch circuit that forms an analog loop that loops the received signal back to the line side, an amplifier installed in the analog loop whose gain value can be switched and set by a control signal, and a level measurement that measures the level of the received input signal. A control circuit that decodes a command indicating an analog loop command from a remote modulation/demodulation device via a main channel, reads the output of the level measurement circuit, outputs a control signal to the amplifier, and operates the switch circuit. said amplifier circuit, and when receiving a command indicating an analog loop command from said remote modem/demodulator, reads the output of said level measuring circuit to prevent said output level from exceeding a predetermined value. 1. A modem test method, characterized in that after setting a gain value, the switch circuit is operated to form an analog loop.