Instruction manual

Page 13
Page 13 of 74 UTY4422-001
SECTION 2
SYSTEM CONFIGURATION
2.1 UNIT OVERVIEW
The UNITY 4422 IRD features several separate hardware components: The DC switching
power supply, the main motherboard, an L-band DVB receiver, front-panel keypad controller
card, a front-panel LCD assembly, and the optional L-band RF switch. The DC switching power
supply provides all internal regulated DC power. When present, the L-band RF switch is
installed in the Module 2 expansion slot, and provides network or (if allowed by the network)
local user selection of up to four separate feeds. The selected RF feed output is connected to the
DVB-compliant L-band receiver card. This card tunes and demodulates the input QPSK carrier,
and then applies two layers of error correction decoding. Its output is the original multiplex
MPEG transport stream which was input to the uplink IF modulator. This stream then feeds the
main motherboard, which demultiplexes out the selected video and audio elemental streams.
These are, in turn, de-compressed and converted back to the original analog source material for
output. Meanwhile, the user may query the IRD using the front-panel keypad for input and the
LCD to read the returned status information.
2.2 BLOCK DIAGRAM DISCUSSION
Refer to Figure 1 (Page 14) for the following discussion.
The DVB-compliant receiver card demodulates the incoming QPSK carrier. It implements one
of five possible FEC rates. The resulting bit stream is parsed back into a byte stream and the
MPEG sync is detected. This aligns a de-interleaver and then the following Reed-Solomon FEC
decoder. The decoded byte stream is output to the main board.
The input to the main board is the multiplexed MPEG2 transport stream. If encryption is active,
then the decryption function is executed. The resulting “clear” transport stream is then fed to the
transport demultiplexer. This device selects the component elemental stream for selected video
and audio programs, as well as the network control data streams. The selected video data is
passed to an MPEG video decoder, which converts the signal to linear digital video. This is then
converted to analog NTSC/PAL in a final encoder for output. Meanwhile, the selected MPEG
compressed audio stream is also routed to a combined decompression and digital-to-analog
converter IC. The output is one stereo pair of audio signals (L and R) on Channel 1 at the back
panel. In addition to the first stereo pair, a digital signal processor monitors and demultiplexes
out another selected digital audio stream, which is also decoded and output as the stereo pair on
Channel 2 at the back panel.