Wegener Communications 4422 - Manual (Page 15)

Page 15
Page 15 of 72 UTY4422-002
SECTION 2
SYSTEM CONFIGURATION
2.1 UNIT OVERVIEW
The UNITY 4422 features several separate hardware components: The DC switching power
supply, the main motherboard, a DVB-ASI input card, front-panel keypad controller card, and a
front-panel LCD assembly. The DC switching power supply provides all internal regulated DC
power. The unit’s input is to the ASI card, mounted as Module 1. That card has two BNC input
connectors and an internal (inside the chassis) connector that connects its output to the
motherboard. This output data stream feeds the main motherboard, which demultiplexes 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 unit
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 16) for the following discussion.
The DVB-compliant receiver card detects the incoming 270 Mbit ASI carrier. The MPEG sync
is detected. The decoded byte stream is output to the main board.
The input to the main board is the multiplexed MPEG2 transport stream. 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 (
DAC ) 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 another selected digital audio stream, which is also
decoded and output as the stereo pair on Channel 2 at the back panel.