Chapter 3. Functional And Physical Descriptions - Comtech EF Data CDM-710 Installation And Operation Manual

Chapter 3. FUNCTIONAL AND
PHYSICAL DESCRIPTIONS
The modem is constructed as a 1RU high rack-mounting chassis, which can be freestanding, if
desired. Rack handles at the front facilitate removal from and placement into a rack.
The satellite modem performs several key functions:
It accepts incoming data from the terrestrial interface and converts it into
appropriate clock and data signals.
The modulator operates on the data to frame and encode it for transmission.
Encoded information is mapped for modulation.
A modulated carrier is transmitted from the IF interface for use by uplink
equipment for delivery to the satellite.
A carrier received from the satellite link is acquired and demodulated to
recover symbols and timing.
Error correction and deframing are performed.
User data is delivered to the to the data interface.
Transmit (Tx) data is delivered to the data interface where it is converted to clock and data signals
for further processing. Depending upon the type of interface, clock and data are provided or in other
cases the clock is embedded in the data and clock recovery is performed to generate clock and data
signals. A First-In –First-Out (FIFO) follows the terrestrial interface to facilitate delivery of the
data to the framing card. Data is passed to the Forward Error Correction (FEC) Encoder where the
data is framed and encoded in accordance with either the DVB-S, DVB-DSNG, or DVB-S2
formats. After encoding the data is passed to the modulator where the I and Q signals are mapped to
generate the appropriate constellation (QPSK, 8-PSK, 16-QAM, 16-APSK, and 32-APSK) and
filtered to provide the desired spectral rolloff. Finally, a carrier is generated by a frequency
synthesizer in conjunction with the I and Q signals to produce a frequency range of:
70/140 MHz:
L-Band:
52 to 88 or 104 to 176 MHz IF output signal at the connector on the modem.
950 to 1950 MHz output signal at the Frequency connector on the modem.
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