Motorola OM 2000 Installation & Operation Manual page 22

2 OVERVIEW
PID 0 and PID 1 packets, as well as commands specifying how often the generator
should insert the packets into the multiplexer.
Generating the RF Output
The RF modulator receives the OOB data transport multiplex created by the packet
multiplexer and performs the following functions to convert it for RF transmission:
Forward error correction
(FEC) encoding
QPSK modulation
Frequency upconversion
Figure 2-4 shows a block diagram of the RF modulator:
Figure 2-4 — RF modulator block diagram
Generating Serial Data Outputs
Depending on the routing, multiplexing, and PID re-assignment definitions contained
in the PID maps, the packet multiplexer directs input packets to serial data port
destination queues and multiplexes them into output datastreams in the same way it
routes and multiplexes data for the RF modulator.
To be valid output destinations, serial data ports must be configured as output ports.
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An FEC encoder performs Reed/Solomon encoding, data
interleaving, and data randomization to reduce transmission errors.
A QPSK modulator converts the digital information in the OOB
transport multiplex into a synthesized analog waveform. The
waveform is a 1.8 MHz-wide signal with a carrier frequency
centered at 44 MHz (IF).
A frequency-agile converter processes the QPSK-modulated 44
MHz IF signal to an RF output frequency configurable from
71 through 129 MHz.