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SDM-300Ls Satellite Modem
Burst Mode Modulator Operation
energy dispersal. There is no need for a differential encoder in burst mode, as the
ambiguities are resolved using the unique word. The data signal passes to the 1/2 rate
Viterbi K=7 convolutional encoder.
The output of the encoder generates two separate data streams to drive the in-phase and
quadrature channels of the modulator. The data signal passes through a set of variable-
rate digital Nyquist filters. There are activity detectors on both the In-phase and
Quadrature (I&Q) channel Nyquist filters.
The digital Nyquist filters are followed by Digital to Analog (D/A) converters and
reconstruction filters. These filters provide proper spectral shaping and equalization. The
filters are under control of the M&C.
The I&Q filtered data signals are applied to the RF modulator, which converts them to a
modulated carrier. The spectral shape will be identical to that of the input data streams,
but double-sided about the carrier frequency.
The RF synthesizer provides the proper frequencies to convert the modulator IF to the
desired output frequency in the 50 to 180 MHz range. The synthesizer has multiple loops,
and incorporates a DDS chip to accommodate 100 Hz steps over a range of 130 MHz.
The RF section has a frequency stability of
The signal from the power combiner is sent to the output amplifier, which amplifies the
low-level signal from the modulator section to the proper level for output from the
module. The amplifier contains circuitry which provides programmable control of the
output level over a range of -5.0 to -30.0 dBm, in 0.1 dB steps. Power leveling is
provided at
temperature.
Note: The data packet must not be less than 48 bits of data. There is no maximum length
for the data packet.
B.2
Specifications
B.2.1
Digital Data Rate
The digital data rate is selectable at 19.2 or 57.6 kbps. The modem automatically
calculates and sets the symbol rate.
±
1.0 dB to maintain the stability of the output level over time and
Modulation Type
Encoding Type
QPSK 1/2
QPSK 1/2
±
1 x 10
.
-5
Data Rate
Viterbi
19.2 kbps
Viterbi
57.6 kbps
B–2
Revision 1
MN/SDM300L3.IOM
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