Comtech EF Data CDM-550T - Manual (Page 21)

Chapter 1. INTRODUCTION
1.1 Overview
The CDM-550T Satellite Modem, shown here in Figure 1-1, is a very low-cost Closed Network
Satellite Modem, intended for both Very Small Aperture Terminal (VSAT) and hub applications.
It offers variable data rates from 2.4 to 2048kbps, in BPSK, QPSK and Offset QPSK modes. Both
Viterbi and Sequential Forward Error Correction (FEC) are provided as standard.
Figure 1-1. CDM-550T
The modem is compact, 1RU high and 12 inches deep, and consumes only 18 watts. It has a front
panel Vacuum Fluorescent Display (VFD) display and keypad for local configuration and
control, although it can be fully remote-controlled.
1.2 Standard Features
IF port impedance is selectable from the front panel. Users may choose between the universal
standard of 50
Ω or the less frequently used 75Ω. The CDM-550T offers both impedances in the
same unit as a standard feature.
To facilitate network management, the CDM-550T incorporates EDMAC, an acronym for
Embedded Distant-end Monitor And Control (EDMAC). In this mode, an additional 5%
overhead is combined with the traffic data, (1.5% in Turbo BPSK modes) which permits M&C
information to be added (transparently to the user), allowing access to the distant-end modem.
This mode does not require any additional cabling at either the local or distant-end Modems -
access to EDMAC is via the standard M&C control port. Full monitor and control is possible, and
importantly, the on/off status of the carrier at the distant-end carrier can be controlled.
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