Theory of Operation
SDM-9000 Satellite Modem
5–14
Rev. 4
The digital data is then sent to four separate circuits:
•
AGC/AOC
•
Carrier recovery (Costas) loop
•
Clock recovery loop
•
Soft decision mapping
The AGC/AOC provides a gain feedback signal to the RF module, and an offset
feedback signal to the offset amplifiers just prior to the Nyquist filters. This closed-loop
control ensures that the digital representation of the I and Q channels is optimized for the
Costas and clock loops, as well as the soft-decision mapping circuitry.
The digital Costas loop, in conjunction with a Direct Digital Synthesizer (DDS),
performs the carrier recovery function. The Costas loop consists of the following circuits
(all implemented digitally):
•
Costas phase detector
•
Loop filter
•
DDS
The DDS performs the function of a VCO in an analog implementation, but can be easily
programmed to the desired center frequency via the local M&C. The output of the DDS
is sent to the RF module and provides the reference to which the quadrature local
oscillator is locked. The local M&C sweeps the local oscillator (via DDS programming)
through the user specified sweep range. When the Viterbi decoder determines that the
modem is locked, the local M&C stops the sweep and begins the de-stress process. This
involves fine tuning the DDS based on the phase error in the Costas loop. The de-stress
process continues as long as the modem is locked. If the carrier is interrupted, the local
M&C resumes the sweep process.
The digital clock loop, in conjunction with the other half of the DDS, performs the clock
recovery function. The clock loop consists of the following circuits (all implemented
digitally):
•
Phase detector
•
Loop filter
•
DDS
Summary of Contents for SDM-9000
Page 2: ......
Page 5: ...8 Mbit s w IDR Figure 1 7 16QAM BER Performance Curves with Reed Solomon Filename T_ERRATA 3...
Page 8: ......
Page 27: ...SDM 9000 Satellite Modem Introduction Rev 4 1 5 Figure 1 3 SDM 9000 Block Diagram...
Page 42: ...Introduction SDM 9000 Satellite Modem 1 20 Rev 4 This page is intentionally left blank...
Page 64: ...Configuration SDM 9000 Satellite Modem 3 6 Rev 4 JP1 Figure 3 4 Interface PCB AS 3971...
Page 65: ...SDM 9000 Satellite Modem Configuration Rev 4 3 7 Figure 3 5 Interface PCB AS 4477...
Page 66: ...Configuration SDM 9000 Satellite Modem 3 8 Rev 4 JP1 JP6 JP7 Figure 3 6 Interface PCB AS 5618...
Page 70: ...Configuration SDM 9000 Satellite Modem 3 12 Rev 4 Figure 3 7 Nyquist Filter Installation...
Page 83: ...SDM 9000 Satellite Modem Operation Rev 4 4 9 This page is intentionally left blank...
Page 87: ...SDM 9000 Satellite Modem Operation Rev 4 4 13 This page is intentionally left blank...
Page 104: ...SDM 9000 Satellite Modem Operation Rev 4 4 31 This page is intentionally left blank...
Page 107: ...Operation SDM 9000 Satellite Modem 4 34 Rev 4 This page is intentionally left blank...
Page 124: ...SDM 9000 Satellite Modem Operation Rev 4 4 51 Figure 4 17 RF Loopback Figure 4 18 IF Loopback...
Page 150: ...Theory of Operation SDM 9000 Satellite Modem 5 22 Rev 4 Figure 5 6 Interface Block Diagram...
Page 158: ...Theory of Operation SDM 9000 Satellite Modem 5 30 Rev 4 This page is intentionally left blank...
Page 186: ...Maintenance SDM 9000 Satellite Modem 6 28 Rev 4 This page is intentionally left blank...
Page 218: ...Options SDM 9000 Satellite Modem A 32 Rev 4 This page is intentionally left blank...
Page 242: ...Remote Control Operation SDM 9000 Satellite Modem B 24 Rev 4 ref SE_ command...
Page 254: ...Glossary SDM 9000 Satellite Modem g 6 Rev 4 This page is intentionally left blank...
Page 256: ...2114 WEST 7TH STREET TEMPE ARIZONA 85281 USA 480 333 2200 PHONE 480 333 2161 FAX...