SDM-309B Satellite Modem
Theory of Operation
MN/U-SDM309B Rev. #
5-5–15
7/8 rate. The "de-puncture" pattern is the same as the "puncture pattern used in the
encoder. A set of "branch metric" values is then computed for each of the received
symbol pairs, related to the probability that the received symbol pair was actually
transmitted as one of the four possible symbol pairs. The "branch metrics" are then
processed by the add-select-compare (ASC) computer. The ASC computer makes
decisions about the most probable transmitted symbol stream by processing the current
branch metrics with the state metrics computed for the sixty-four previous decoder
inputs. The results of the ASC computer are stored in memory called path memory. The
path memory is 80 states in depth. The path with the maximum metric is designated as
the survivor path and its data is used for output. The difference between the minimum
and the maximum path metric’s is used as the means of determining synchronization of
the decoder. The output data may then be descrambled and differentially decoded. Both
of these processes are optional and may be selected by the user locally or remotely. The
data out of the differential decoder is sent to the interface card for formatting and output.
The synchronization signal is used for Lock Detect and sent to the M & C.
The Raw BER count is generated from the minimum and maximum metric’s and sent to
the M & C for further processing
5.3 Demodulator
5.3.1 General Description
The modem Demodulator card is a 10.25" x 14" card (Figure 5-9) that fits in the lower
left slot of the modem chassis. Its function is to accept a desired QPSK modulated signal
in the 50 to 90 MHz or 100 to 180 MHz range and convert it to filtered baseband in-
phase and quadrature signals which are then quantized and output from the card.
Several subSections make up the card. These include:
1) The AGC Amplifier
2) The Quadrature Demodulator
3) The RF Synthesizer
4) The Nyquist Filter
5) The Baseband Amplifier
6) The Soft Decision Interface
A block diagram of the Demodulator is shown in Figure 5-10. A detailed description of
the subSections appears in Section 5.3.3
Summary of Contents for SDM-309B
Page 7: ...Preface SDM 309B Satellite Modem iv Rev 0 This page is intentionally blank ...
Page 13: ...Table of Contents SDM 309B Satellite Modem x Rev 0 This page is intentionally blank ...
Page 16: ...SDM 309B Satellite Modem Introduction MN U SDM309B Rev 1 1 3 Figure 1 1 SDM 309B Modem ...
Page 18: ...SDM 309B Satellite Modem Introduction MN U SDM309B Rev 1 1 5 Figure 1 3 Modular Construction ...
Page 25: ...Introduction SDM 309B Satellite Modem 1 1 12 MN U SDM309B Rev ...
Page 28: ...SDM 309B Satellite Modem Installation MN U SDM309B Rev 2 2 3 Figure 2 1 Rear Panel View ...
Page 34: ...SDM 309B Satellite Modem Operation MN U SDM309B Rev 3 3 Figure 3 1 Front Panel View ...
Page 47: ...Operation SDM 309B Satellite Modem 3 16 MN U SDM309B Rev Figure 3 2 Menu Tree ...
Page 48: ...SDM 309B Satellite Modem Operation MN U SDM309B Rev 3 17 Figure 3 3 Menu Tree ...
Page 49: ...Operation SDM 309B Satellite Modem 3 18 MN U SDM309B Rev Figure 3 4 Menu Tree ...
Page 50: ...SDM 309B Satellite Modem Operation MN U SDM309B Rev 3 19 Figure 3 5 Menu Tree ...
Page 51: ...Operation SDM 309B Satellite Modem 3 20 MN U SDM309B Rev Figure 3 6 Menu Tree ...
Page 52: ...SDM 309B Satellite Modem Operation MN U SDM309B Rev 3 21 Figure 3 7 Menu Tree ...
Page 53: ...Operation SDM 309B Satellite Modem 3 22 MN U SDM309B Rev Figure 3 8 IF Loopback ...
Page 54: ...SDM 309B Satellite Modem Operation MN U SDM309B Rev 3 23 Figure 3 9 RF Loopback ...
Page 55: ...Operation SDM 309B Satellite Modem 3 24 MN U SDM309B Rev Figure 3 10 Interface Loopback ...
Page 56: ...SDM 309B Satellite Modem Operation MN U SDM309B Rev 3 25 Figure 3 11 Baseband Loopback ...
Page 71: ...Operation SDM 309B Satellite Modem 3 40 MN U SDM309B Rev Figure 3 12 Menu Tree ...
Page 72: ...SDM 309B Satellite Modem Operation MN U SDM309B Rev 3 41 Figure 3 13 Menu Tree ...
Page 73: ...Operation SDM 309B Satellite Modem 3 42 MN U SDM309B Rev Figure 3 14 Menu Tree ...
Page 74: ...SDM 309B Satellite Modem Operation MN U SDM309B Rev 3 43 Figure 3 15 Menu Tree ...
Page 75: ...Operation SDM 309B Satellite Modem 3 44 MN U SDM309B Rev Figure 3 16 Menu Tree ...
Page 76: ...SDM 309B Satellite Modem Operation MN U SDM309B Rev 3 45 Figure 3 17 Menu Tree ...
Page 77: ...Operation SDM 309B Satellite Modem 3 46 MN U SDM309B Rev ...
Page 88: ...SDM 309B Satellite Modem M C and Interfaces MN U SDM309B Rev 4 4 11 Figure 4 4 IBS Fault Tree ...
Page 89: ...M C and Interfaces SDM 309B Satellite Modem 4 4 12 MN U SDM309B Rev Figure 4 5 Jumper Table ...
Page 127: ...SDM 309B Satellite Modem Theory of Operation MN U SDM309B Rev 5 5 3 Figure 5 1 Modulator Card ...
Page 151: ...Maintenance SDM 309B Satellite Modem 6 6 6 MN U SDM309B Rev Figure 6 3 Typical Eye Patterns ...
Page 177: ...SDM 309B Satellite Modem Data Rates and Filters MN U SDM309B Rev A 9 ...
Page 235: ...External Channel Unit SDM 309B Satellite Modem C C 28 MN U SDM309B Rev Figure C 13 Menu Tree ...
Page 236: ...SDM 309B Satellite Modem External Channel Unit MN U SDM309B Rev C C 29 Figure C 14 Menu Tree ...
Page 237: ...External Channel Unit SDM 309B Satellite Modem C C 30 MN U SDM309B Rev Figure C 15 Menu Tree ...
Page 238: ...SDM 309B Satellite Modem External Channel Unit MN U SDM309B Rev C C 31 ...
