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2 OVERVIEW
PID 0 and RID 1 packets, as well as comnnands 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:
F o r w a r d e r r o r c o r r e c t i o n
(PEC) encoding
Q P S K m o d u l a t i o n
Frequency upconversion
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 syntfiesized 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 OPSK-modulated 44
MHz IF signal to an RF output frequency configurable from
71 through 129 MHz.
Figure 2-4 shows a block diagram of the RF modulator:
Figure 2-4 — RF modulator block diagram
From packet
m u l t i p l e x e r
F E C
e n c o d e r
Q P S K
m o d u l a t o r
Frequency
c o n v e r t e r
R F
T o
R F
▶
d i s t r i b u t i o n
7 1 - 1 2 9 M H z s y s t e m
4 4
M H z
c o n v e r t e r
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.
12
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