Comtech EF Data CDM-710 Installation And Operation Manual page 29

CDM-710 Broadcast Satellite Modem
Introduction
The CDM-710 is constructed as a 1RU-high rack-mounting chassis, which can be freestanding, if
desired. Handles at the front facilitate removal from and placement into a rack.
The CDM-710 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 as follows:
CDM-710 (70/140 MHz):
CDM-710L (L-Band):
An Rx carrier from the satellite is received by the demodulator and reverses the process
performed by the modulator. The demodulator has an FEC decoder that corrects errors incurred
during transmission to improve the integrity of the data delivered to the data interface. A
synthesizer in the demodulator is programmed to select the desired carrier from the transponder.
52 to 88 or 104 to 176 MHz IF output signal at the connector on the
modem.
950 to 2000 MHz output signal at the Frequency connector on the
modem.
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Revision 11
MN/CDM710.IOM