Comtech EF Data CDM-700 - Manual (Page 36)

CDM-700 High Speed Satellite Modem Revision 5
Functional Description MN/CDM700.IOM
After the IF sampling, the processing is all digital, including demodulator, phase lock loops,
Nyquist filters and adaptive equalizer. The resultant demodulated signal is fed, in soft decision
form, to the selected FEC decoder.
After decoding, the recovered clock and data pass to the Framer card, where the error corrected
data stream is Demultiplexed (Demux) and directed to the individual data ports of each data
interface. Depending upon the type of data interface, the data passes to the Plesiochronous/
Doppler buffer, which has a programmable size, or alternatively bypasses the buffer. From here,
the receive clock and data signals are routed to the terrestrial interface, and are passed to the
externally connected DTE equipment.
Physically, the CDM-700 modem comprises several main card assemblies. Refer to Figure 3-1
for a functional block diagram.
• Data Interface: There are two slots at the rear of the modem that where accept the
available data interfaces are plugged into the modem. The data interfaces are single port
and multi-port type:
♦
A single port interface provides a duplex path. Most are capable of simplex Tx and
Rx operation as well as full duplex operation
♦
A multi-port interface has more than one data interface. For example, the Dual
G.703 (CDI-10) interface has two ports and each Tx/Rx port is independently
programmed for E3, T3, or STS-1 operation.
• The Framer card is part of the base modem and includes the Mux/Demux and
microcontroller. It also provides the remote and Ethernet ports plus the alarm interface.
The keypad and display are also controlled from the framer card.
• FEC: There are two expansion slots for error correction. Currently, one is used. These
slots are within the modem and require removal of the cover to access. They look similar
to SIM memory modules and are located near the front of the chassis on the Framer card.
• The Modulator card (70/140 MHz or L-Band) is a plug-in board that sits atop the Framer card.
• The Demodulator card (70/140 MHz or L-Band) also plugs into the Framer card.
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