Comtech EF Data QAM256 - Manual (Page 15)

QAM256 Digital Video Modulator and Upconverter Theory of Operation
TM077 – Rev. 4.0 3-1
Theory of Operation
3
3.0 Theory of Operation
A digital terrestrial interface supplies the modulator with a data stream. The data stream is
synchronized if the incoming stream is framed. The data is scrambled, and FEC is added. The
data is then convolutionally encoded, punctured, then constellation mapped. The resulting I&Q
symbols are digitally filtered. The data is then converted into an analog waveform and is vector
modulated onto an RF Carrier produced from the Transmit IF Synthesizer Circuitry.
3.1 QAM256 Operation
A block diagram of the signal flow is shown in Figure 3-1 below.
Figure 3-1. Functional Block Diagram