16Apsk And 32Apsk - Comtech EF Data CDM-710 Installation And Operation Manual

CDM-710/L Broadcast Satellite Modem
Introduction
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 the
DVB-S, DVB-DSNG, or DVB-S2 formats.
After encoding, the data is passed to the modulator where the I&Q signals are
mapped to generate the appropriate constellation (QPSK, 8PSK, 16QAM,
16APSK, and 32APSK) and filtered to provide the desired spectral rolloff.
Finally, a carrier is generated by a frequency synthesizer in conjunction with the
I&Q signals to produce a frequency range, as follows:
• CDM-710 (70/140 MHz), 52 to 88 MHz or 104 to 176 MHz IF output
signal at the rear panel connector
• CDM-710L (L-Band), 950 to 2000 MHz output signal at the rear panel
frequency connector
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.
Physically, the CDM-710/L is comprised of several main card assemblies:
• The optional Data Interface Modules may be quickly plugged into or
removed from the rear panel interface slots.
CAUTION
You must first power down the unit in order to install or
remove a data interface module. Any attempt to install or
remove a module without first turning off the power to the unit
will result in damage to the data interface.
• The Framer Card receives signals from the data interface card and routes
signals to the FEC Encoder and Modulator. The microcontroller for the
unit also resides on the Framer Card and is the embedded controller for
1–6
MN/CDM710.IOM
Revision 12