Echo Suppressors for Long Telephone Circuits

A device has been developed by the Bell System for suppressing ``echo´´ effects which may be encountered under certain conditions in telephone circuits which are electrically very long. This device has been given the name ``echo suppressor´´ and consists of relays in combination with vacuum tubes, which are operated by the voice currents so as to block the echoes without disturbing the main transmission. This paper gives a brief description of this device, together with a discussion of its possibilitie and limitations. A number of echo suppressors have been operated on commercial telephone circuits tor a considerable period so that their practicability has been demonstrated.