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DMD50 Universal Satellite Modem
Theory of Operation
3.0 Modem Hardware
The modem is based on a two printed circuit card (minimum configuration) design with additional
optioned printed circuit cards available for additional features. The minimum configuration
consists of an L-Band/IF Assembly and a Digital Baseband Assembly. The optional printed circuit
cards include a Turbo Codec printed circuit card and one of several types of Interface printed
circuit card (refer to Appendix A). A block diagram of the DMD50 is shown in Figure 3.1.
3.0.1 L-Band/IF Printed Circuit Card
The L-Band/IF Printed Circuit Card consists of an analog modulation function, an analog complex
downconversion, and two wide-band digital synthesizers. The block diagram of the L-Band/IF
Assembly is shown in Figure 3-2.
In the modulator, analog in-phase (I) and quadrature (Q) signals are generated on the Digital
Baseband Printed Circuit Card, routed to the L-Band/IF Printed Circuit Card, and modulated at
the desired frequency. The L-Band or 70/140 modulated signal is then passed through a
microprocessor controlled variable attenuator providing gain control of the output signal.
TM118 – Rev. 1.1
Figure 3-1. Block Diagram
Theory of Operation
3
3-1
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