GB1510162A - Echo traps - Google Patents

Abstract

1510162 Echo suppressors SIEMENS AG 27 June 1975 [24 July 1974] 27285/75 Heading H4R In an echo suppressor provided on the four wire side of a hybrid junction a normally transmissive blocking device 3, Fig. 6, is provided in the transmit path together with an attenuation element 4 in the receive path, with a switch 41 which is normally in a position to by-pass the attenuation element. A control circuit detects a signal in the receive path and, in the absence of signal in the transmit path, causes the blocking element 3 to block the transmit path. When a signal is detected in both paths operation of blocking element 3 is inhibited but the switch 41 is operated to insert the attenuation element, but is arranged so that as the signal in the transmit path increases relative the signal in the receive path the attenuation of the attenuation element is reduced and/or the switch 41 is allowed to revert and by-pass the attenuation element. As described the signal in the transmit and receive paths can be compared in comparator 8 and the output caused to increase the attenuation 43 in the control path of a compressor 42, 43, 4, or, Fig. 2 (not shown) the output of comparator 8 can be used to inhibit the operation of AND gate (47) controlling switch 41. Alternatively control of the attenuator 43 in the compressor 42, 43, 4, can be effected via a threshold device coupled either to the output of comparator 6, Fig. 4 (not shown) or the output of signal detector 62, detecting the signal in the transmit path, Fig. 5 (not shown). A further modification, Fig. 4, includes a variable gain amplifier 71 in the transmit path signal detector circuit and a variable attenuator 73 in the receive path signal detector circuit which are both controlled in accordance with signal level in the respective path via a storage control device 70 which is blocked by controller 60 during duplex operation. The arrangement varies the control sensitivity in accordance with the hybrid junction attenuation. A delay device 65 is provided in the receive path speech detector to compensate for the delay through the hybrid junction.