The CDM-550 is a low-cost, high performance satellite modem designed for closed network Single Channel Per Carrier (SCPC) links. It is ideal for many VSAT applications.
The CDM-550 offers a range of data rates from 2.4 kbps to 2048 kbps in 1 bit per second steps. The modem includes Viterbi or Sequential forward error correction as standard. A Reed-Solomon Codec and Turbo Product Codec are available as extra-cost options.


Turbo Product Coding (TPC) is a recent development in FEC techniques that delivers significant performance improvement when compared to Viterbi with concatenated Reed-Solomon. TPC simultaneously offers increased coding gain, lower decoding delay, and bandwidth savings of up to 40%. Two modes are included that permit operation from exceptionally small antennas, where flux density issues are of concern. (The Turbo Product Codec is an extra-cost option.)


Another special feature of the CDM-550 is the universal data interface. The user data can be EIA422/EIA530, V.35, X.21, or synchronous/asynchronous EIA-232. The interface is selectable from the front panel or via remote control. Any asynchronous EIA-232 data protocol is automatically recognized by the modem, thus alleviating extensive operator setup. The modem is capable of G.703 T1, or E1 rates by attaching the CIC-50 Interface Converter to the data port.


The modem includes several Loopback modes, which facilitate troubleshooting and diagnosis. An internal IF loopback permits testing of the entire modem without the need for external cables and attenuators. Digital loopback permits testing of the digital baseband, and the I/O loopback permits testing of the data interface chip set. The I/O loop is bi-directional.


A special feature of the CDM-550 is its ability to monitor and control the distant end of a satellite link using a Comtech EFData proprietary overhead channel. This framed mode is called EDMAC (Embedded Distant-end Monitor and Control). User data is framed and extra bits are added to pass control, status, and automatic uplink power control information. This process is completely transparent to the user.
Comtech RF transceivers may be controlled from the front panel of the modem using a low data rate FSK signal on the Rx IF cable. An RF transceiver at the distant end of a satellite link may also be controlled and monitored through the EDMAC channel.


The CDM-550 is an extremely compact 1 rack-unit (1U) high and 12 inches deep. It is equipped with a universal power supply (100 to 240 volts AC) and consumes a maximum of 25 Watts. The modem meets current CE and FCC Part 15 requirements for safety, emissions, and immunity.


SatMac, a Windows-based monitor and control program, is available for configuring the local and distant end modems, transceivers, and redundancy switches.
Modem redundancy switches include the CRS-100 1:1 switch module and the CRS-200 1:10 switch. Both provide significantly enhanced link availability.

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