10
LDM-144LR
2. Introduction
2.1 General
The LDM-144LR is a short-range modem for synchronous transmission, full
or half duplex, over unconditioned lines. The LDM-144LR has a range of up
to 26.5 km (16.5 miles) and operates at selectable data rates from 48 kbps to
144 kbps.
The modem uses a unique modulation technique named Partial Response,
Class IV (PR4) in order to:
• Provide background noise immunity
• Eliminate normal line distortion
• Enable efficient transmission and reception of serial data over a twisted
pair cable
• Provide extended range
The LDM-144LR is coupled to the line through isolation transformers,
which in conjunction with protective circuitry, safeguard against AC or DC
overvoltages. The protective circuitry enables operation even when DC is
connected to the line.
The LDM-144LR transmit timing is internally provided, or externally
derived either from the data terminal or from the receive signal. The receive
timing is always regenerated from the receive signal.
The LDM-144LR features V.54 diagnostic capabilities for performing local
analog loopbacks and local and remote digital loopbacks. In the digital
loopback mode, the operator at either end of the line may test both modems
and the line. The loopback is controlled either by the front-panel
pushbuttons or through the DTE interface. Three DTE digital interface
options are available:
• RS-232/V.24 (up to 128 kbps)
• V.35
• RS-530
