| 摘要 |
<p>Telephone instrument is designed for both two-wire analogue working into the local exchange and also four wire digital working into a local exchange. The instrument has been designed for use with the existing two-wire analogue network but with facility to connect it to an overlay digital network so that it is permanently connected for service to both. The instrument contains the usual facilities, transmitter, dial or equivalent, number store etc., and also analogue/digital converters. For analogue working the line (18') from the analogue local exchange (6) is connected through a hybrid (45) in the instrument, along a common two wire bus (43) to a second hybrid (42) and off to the purely analogue section (18, 20). For digital working, the instrument has a four wire connection (19') to the exchange (9) so that incoming signals are connected to an A/D or D/A converter (44), into the hybrid (45), along the bus (43), hybrid (42), and digital originated signals into the digital section (21) of the instrument. Another alternative has no bus (43) but direct analogue or digital connection with switched changeover.</p> |
