Chapter 5. Theory Of Operation; Modulator - Comtech EF Data SDM-650B Installation And Operation Manual

This chapter contains information on the following cards:
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In addition, information is provided on reacquisition, fast acquisition, and the directed
sweep mode.

5.1 Modulator

The modem modulator card is a 10.25" x 14" card that fits in the top-left slot of the
modem chassis.
The modulator creates a QPSK or BPSK modulated carrier within the 50 to 90 MHz, or
100 to 180 MHz range, from the digital data stream provided by the interface card.
Several subsections make up the card:
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Rev. 6
THEORY OF OPERATION
Modulator
Sequential decoder/demodulator processor
Demodulator
Digital interface
Scrambler/differential encoder
Convolutional encoder
I/Q Nyquist filters
Modulator
Output amplifier
RF synthesizer
Clock synthesizer
Chapter 5.
5–1