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
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.