Echo Canceller Test Procedure | Echo Cancellation Test Equipments

This page describes Echo Canceller Test Procedure. It mentions Echo Cancellation Test Equipments. Echo canceller is the equipment used for echo cancellation. The echo canceller measurements performed by this test procedure include return loss, line rate, jitter, ERLE, continuity, tone disabler (data transmission, in-band signaling) etc.

About Echo Canceller:
The device mainly used in telecommunication networks to eliminate or reduce the echo is known as echo canceller. It uses advanced DSP algorithms to perform echo cancellation. Following section mentions various measurements performed on the echo canceller as part of test evaluation.
Refer echo canceller basics >> for more information.

Echo Cancellation Test Equipments

Following is the list of test equipments used for Echo Cancellation.
• Sweep Signal Generator
• Spectrum Analyzer
• Directional Coupler
• Termination
• 75 Ohm unbalanced to 120 Ohm balanced Transformer
• PCM Channel Test set
• Oscilloscope
• Digital Transmission Analyzer
• Jitter Modulator Oscilloscope
• 3dB and 6dB pad
• DC regulated power supply
• Digital volt meter

Test procedure for echo canceller measurements

Let us understand test procedure for various test and measurements as part of echo canceller evaluation in the lab and in the field.

Output Port Return Loss

• Connect the test equipments as shown in the fig-1.
• Set the sweep signal generator to the desired frequency.
• connect the signal generator to input port of directional coupler and output port to spectrum analyzer.
• calibrate spectrum analyzer by shorting coupled port of directional coupler.
• Now connect the output port of canceller to coupled port of directional coupler and note down readings.
• The difference between these two readings will give return loss of the output port.

Perform the above steps for input port return loss with suitable changes for the input port instead of output port as measurement port. Record the measurements as per format mentioned in the table-1 below.

Pulse Mask Measurement

Line coding used should be HDB3 as per ITU-T Rec. G.703. Output pulse characteristics can be measured by two methods.
• Pulse Mask Method
• CRO method

In pulse mask method, pulse mask is placed at the front end screen of CRO. Now output pulse characteristics may be observed. If the output pulse falls within ITU-T pulse mask then it is treated as OK. CRO method is described below.

• Make the connections as per figure-2.
• Feed 2 Mbps data to Si port of echo canceller.
• Connect So port to CRO through two 60 Ohm resistors as shown.
• Measure pulse characteristics of both +ve and -ve pulses and results are tabulated as shown in table-2.
• Repeat the above echo canceller test procedure for receive output port also.

Line Rate Measurement

• Connect Ro port of echo canceller to DTA Rx as shown in figure-3.
• Read ppm offset on the instrument.
• Then connect So port of echo canceller to DTA Rx and take measurement as above.
• Record the same in the table-3 below.

Input Jitter Tolerance

• Feed framed jittery data from the jitter modulation oscillator and digital transmission analyzer to Ri port of echo canceller. The pattern of data should be HDB3 coded 2¹⁵-1 PRBS of frequency and amplitude as defined in the figure-3/G.823 table 2/G.823.
• Short the Ro and Si ports.
• Connect output port So to DTA receiver.
• Adjust jitter frequency to 20 Hz.
• Increase the amplitude until the local LED on SEND out port glows.
• Reduce amplitude until LED turns OFF. Note down the amplitude.
• Repeat the same for various frequencies as per table.
• Repeat the same test procedures by feeding jittery data at SEND IN port and monitor at REC OUT port (Short So and Ri ports).

Echo Return Loss Enhancement (ERLE) Measurement

ERLE (Center Clipper Enabled i.e. NLP ON-ERL 6dB

• Connect the equipment as shown in fig-6.
• Using front select and advanced switches, select ERL 6 dB.
• Select NLP mode on front panel. Press advance switch to go to ON option.
• Feed 1 KHz, -10 dBmo audio signal to 4W Tx points of far end primary MUX channel-1.
• Connect a 6 dB pad between 4W Tx and 4W Rx of near end primary MUX channel-1.
• Connect 4W Rx of channel-1 (far end MUX) to audio analyzer analog IN port.
• Record the received level. It should be >65 dB.
• Repeat the same test procedure for all the 30 channels.

ERLE (Center Clipper Enabled i.e. NLP ON-ERL 3dB

• Connect the equipment as shown in fig-7.
• Using front select and advanced switches, select ERL 3 dB.
• Select NLP mode on front panel. Press advance switch to go to ON option.
• Feed 1 KHz, -10 dBmo audio signal to 4W Tx points of far end primary MUX channel-1.
• Connect a 3 dB pad between 4W Tx and 4W Rx of near end primary MUX channel-1.
• Connect 4W Rx of channel-1 (far end MUX) to audio analyzer analog IN port.
• Record the received level. It should be >62 dB.
• Repeat the same test procedure for all the 30 channels.

ERLE (Center Clipper Disabled i.e. NLP OFF-ERL 6dB

• Connect the equipment as shown in fig-8.
• Using front select and advanced switches, select ERL 6 dB.
• Select NLP mode on front panel. Press advance switch to go to OFF option.
• Feed 1 KHz, -10 dBmo audio signal to 4W Tx points of far end primary MUX channel-1.
• Connect a 6 dB pad between 4W Tx and 4W Rx of near end primary MUX channel-1.
• Connect 4W Rx of channel-1 (far end MUX) to audio analyzer analog IN port.
• Record the received level. It should be >35 dB.
• Repeat the same test procedure for all the 30 channels.

ERLE (Center Clipper Disabled i.e. NLP OFF-ERL 3dB

• Connect the equipment as shown in fig-9.
• Using front select and advanced switches, select ERL 3 dB.
• Select NLP mode on front panel. Press advance switch to go to OFF option.
• Feed 1 KHz, -10 dBmo audio signal to 4W Tx points of far end primary MUX channel-1.
• Connect a 3 dB pad between 4W Tx and 4W Rx of near end primary MUX channel-1.
• Connect 4W Rx of channel-1 (far end MUX) to audio analyzer analog IN port.
• Record the received level. It should be >32 dB.
• Repeat the same test procedure for all the 30 channels.

Continuity check tone:2000 Hz as per ITU-T CCS-6 and CCS-7

• Make the test setup as shown in fig-10.
• Select signaling tone disabler mode and press advance switch to option C6/C7.
• Feed 2000 Hz analog signal at -10dBmo.
• Record the received analog level in the table-10 below.

Tone disabler (for data transmission)

• Detection band: mandatory 2079 to 2121 Hz. Optional 1950 to 2079 Hz and 2121 to 2250 Hz.
• Detection threshold: -33 dBmo +/- 2 dB at 2100 Hz.

• Make the setup as shown in fig-11.
• Select data tone disabler mode and press advance switch to 2100 option.
• select 2079 Hz at -10 dBmo from PCM channel test set. connect the test setup as shown in the fig-11.
• Record the received data tone level.
• Change the frequency to 2121 Hz from PCM channel test set and repeat the same test procedure.
• set the frequency in channel test set to 2100 Hz and feed -31 db and repeat the same test procedure.
• then change the level to -33dBm, -35dB and repeat the same.

Tone disabler (for in-band signaling at 2600 Hz)

• Detection band: 2600/2400 Hz.
• Detection threshold: Disabling will occur in the detection band for signals greater than -19 dBmo and will not occur for signals less than -22dBmo.
• Connect the test setup as shown in the figure-12 and perform test procedure similar to the one described above.

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