Comtech EF Data SDM-2020 - Manual (Page 28)

SDM-2020 Satellite Demodulator Revision 4
Introduction MN/SDM2020D.IOM
1–2
The modulator and demodulator are intended for use in commercial applications for
transmission and reception of digitized video signals. The Moving Pictures Exported
Group-2 (MPEG-2) defines the basic digitized video format supported (see ISO/IEC DIS
13818-1, Coding of moving pictures and associated audio).
The demodulator also has adative equalization capability. A general block diagram for
the demodulator is shown in Figure 1-2.
Figure 1-2. Demodulator Block Diagram
Selecting the appropriate data interface supports other formats including unframed data.
The demodulator uses a plug-in data interface module installed in the rear of the chassis.
The data interface module provides flexible adaptation to the various physical and
electrical interfaces found in the communications industry. Refer to Appendix A for a
detailed description of the data interface module.
The data rate of the demodulator is programmable from 1.5 to 100
Mbps , with maximum
symbol rates up to 37.5 Msys/s depending upon the modulation, code rate, and data
interface. Demodulation formats include QPSK, 8-PSK and 16-QAM. Operation is based
upon the DVB standard. Refer to Appendix B for detailed remote control operation.
The demodulator incorporates concatenated error correction coding for improved signal
quality. With concatenated coding, an outer Reed-Solomon Codec is used in tandem with
an inner Viterbi or trellis-type Codec. The Reed-Solomon coding is DVB (based on 204,
188, t=8 type code), while the Viterbi and trellis codes are based upon a constraint length
K = 7 convolutional coding. This combination significantly reduces the required
operating power of the satellite system.
The demodulator is a completely self-contained unit in a standard, one-unit (1U) 19-inch
(48.26 cm) rack-mountable enclosure. It includes a backlit LCD display and a standard
Comtech EF Data six-button keypad for user control. Prime power is alternating current
(AC) input or optionally direct current (DC) input. The IF input to the demodulator is
L-Band or 70/140 MHz IF.
A status and control port (available through a 9-pin D connector at the rear of the chassis)
provides either serial EIA-232 or EIA-485 (2- or 4-wires) for remote control applications.
A second rear panel 9-pin D connector provides fault/alarm status.
5611
L-Band Or
70 / 140 MHz
Tuner
Synthesizer
Carrier &
Symbol
Recovery
Viterbi / Trellis
Decoder &
Sync
De-interleaver
RS Decoder
Descrambler Plug-In
Data
Interface
Remote Port
& Faults
User
Interface
User
Interface
Rx
IF
M&C
LNB
Voltage