Patent GB-1316791-A (GB)
Title: Apparatus for and methods of testing echo suppressors
IPC: H04B17/00
Filed: 1970-05-21
Abstract: 1316791 Echo suppressor testing WESTERN ELECTRIC CO Inc 21 May 1970 [22 May 1969] 24562/70 Heading H4R Apparatus for testing echo suppressors includes means for selectively generating test signals arranged to test particular characteristics of the suppressor, means for selectively applying test signals in a number of different arrangements, and means to derive outputs indicative of the acceptability of the characteristics of the suppressor tested by the apparatus. As described with respect to Fig. 1 the apparatus includes a master unit 110 with a transmitter 111 including a number of oscillators the outputs from which can be applied, suitably modulated under the control of control unit 113, to output lines 125. The signals on lines 125 are applied, under the control of test boards 120, to the appropriate trunk 130 to be tested, and to an auxilliary trunk 140. The resulting signals from the line are applied to the receiver 112 where they are compared with reference levels to determine the acceptability of the echo suppressor action. To initiate testing the test board controls the transmission of signals to loop the auxilliary trunk 140 to the trunk, 130, under test via the loop around unit 150. The loop around unit 150 contains a 1000 Hz oscillator operative at a reference level which is used, by comparison with a signal transmitted through the auxilliary trunk, to set the gain of the auxilliary trunk to a reference value. The unit 150 also contains a 2À1 KHz band stop filter to enable a signal at this frequency applied to auxilliary trunk HO to disable the echo suppressors in the auxilliary trunk without being transmitted through to the trunk under test. To test the suppressors a monitoring signal of 2À75 KHz is applied at a level such as not to operate the suppressors. In addition a pulsating signal at 1 KHz is applied first at a level such as should not operate the suppressors and again at a level such as should operate the suppressors, and the effect on the level of the monitoring signal of 2À75 KHz is detected by the receiver, by comparison with reference levels therein, to determine whether the suppressor is operating correctly. In addition by observing the time of change in level of the monitoring signal relative the timing of the pulses in the 1 KHz signal the "pick-up" and "hangover" times of the echo suppressor can be determined. The system of connection of the 1 KHz and 2À75 KHz signals to the auxilliary and test trunks is controlled to provide testing of suppressors at a desired end of the trunk under test on either the odd or even sides. "Break-in" can be tested by applying a 1 KHz signal in one direction on the test trunk, e.g. by application direct to line 133 or to 134 via the auxilliary trunk, to capture the suppressors and cause attenuation to be inserted in the reverse direction, and applying a pulsating 1 KHz signal in the other direction on the test trunk, first at a level which should be insufficient to cause break-in and subsequently at a level to cause break-in, the effect on a low level 2À75 KHz monitoring tone being noted at the receiver to check correct break-in operation. In addition suppressor disabling can be checked by applying the 2À1 KHz disable signal to the test trunk and checking that suppressor operation is absent on transmission of a 1 KHz pulsating signal of level which would normally operate the suppressors. By transmitting the 2À1 KHz disabling signal in pulse form together with 1 KHz pulsating signal of level sufficient to operate the suppressor and a 2À75 KHz monitor signal the suppressor guard against disabling signal imitations in normal transmission is tested. Block diagrams, and/or circuits of the transmitter, receiver, control units, and the loop around unit, are shown and described. The particular test to be performed may be set up manually or may be automatically programmed.