Comtech EF Data SDM-650B - Manual (Page 125)

Rev. 6 5–1
Chapter 5.
THEORY OF OPERATION
This chapter contains information on the following cards:
• Modulator
• Sequential decoder/demodulator processor
• Demodulator
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:
• Digital interface
• Scrambler/differential encoder
• Convolutional encoder
• I/Q Nyquist filters
• Modulator
• Output
amplifier
• RF synthesizer
• Clock synthesizer