10
ASYNC/SYNC 2-WIRE SHORT-HAUL MODEMS
2. Introduction
The Async/Sync 2-Wire Short Haul Modem (A/S2W SHM) operates synchronously
or asynchronously at high speeds (600 bps to 128 Kbps) and in full duplex over
one pair of dedicated telephone lines. It has a range of 3.4 miles (5.5 km) over
26-AWG wire.
The A/S2W SHM operates in full duplex over 2 wires by using the adaptive
“echo-canceling” technique. Because it also uses 2B1Q line coding, it can achieve
the range mentioned above no matter what the data rate is.
The A/S2W SHM incorporates interface circuits for the terminal/computer, an
adaptive echo-canceler, an automatic adaptive equalizer, a modulator, and a
demodulator. It is coupled to the telephone line through an isolation transformer,
which protects against AC or DC overvoltages. The protection circuitry would
enable the unit to operate even if DC were accidentally connected to the line.
The A/S2W SHM has diagnostic capabilities: It can perform local analog
loopback and local and remote digital loopback. The operator at either end of the
line may test both modems and the line in the remote digital loopback mode.
Loopback can be controlled with either the unit’s front-panel pushbuttons or
signals passed through the DTE (PC, data-terminal) interface.
Summary of Contents for ME375A-R2
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