Wegener Communications UNITY 4600 - Manual (Page 33)

wegener.com 800032-01 Rev. G 27
C
HAPTER
3 O
PERATION
This chapter provides an overview of Unity 4600 operation, details of controls and
indicators, the alarm/warning system, and user interface details.
3.1 Theory of Operation
Functional
summary From one selected RF input feed, the Unity 4600 receives an L-band RF carrier from
an external antenna LNB. It then demodulates the carrier and extracts the transmitted
MPEG transport stream. If the stream is scrambled and the unit is properly authorized,
it applies the descrambling algorithm to re-generate that transport stream as it
appeared at the multiplexer in the uplink compression system. (Alternately, if using
per-program viewing access, only the authorized programs will be descrambled.) This
transport stream is then supplied to the ASI transport output, perhaps with program re-
mapping or conditional DPI filtering (under network control). The
Unity 4600 also
decompresses the components of a selected program and provides the audio, video,
and/or data services for output.
Note: The user or network may wish to have a null program assignment if no
attempt at local decompression is desired. This is required for the new HD
programming.
As needed, auxiliary functions are also provided, such as re-insertion of vertical
blanking interval data (closed captioning for example) in the video output. 3.1 presents
a logical block diagram of
Unity 4600 operation.
Available outputs from the Unity 4600 include:
DVB-ASI transport output with program (number and descriptor) mapping
Decompressed MPEG video as composite video output (NTSC or PAL)
Two independent, decompressed audio streams (MPEG or Dolby AC-3 downmix) to
balanced analog audio outputs
Re-insertion of VBI line data from various proprietary and ATSC protocols
Alarm relay
User control relays for cueing
DTMF cueing tones
Front-panel audio (one stereo pair) and composite video monitor outputs
Automated
recovery If unable to deliver required services to predetermined standards, or if unable to detect
a required network control stream (COMPEL
®
), the Unity 4600 attempts to resume
normal operation through a process called Automated Recovery. Referring to an
internal, non-volatile list of "presets", the
Unity 4600 will attempt to restore either
services or network control, depending on what caused the recovery. A "preset" is a
list of unit settings, and the list of these presets is called the Preset Table. Automated
Recovery will attempt to restore the unit according to each preset (one at a time) in the
order in which they are listed in the table. The process continues (repeating attempts if
necessary) until the unit successfully resumes normal operation or is halted by local
user command. If successful with a preset, the settings in that preset become the
permanent unit settings. Later, the local user (or the network, if available) may abort the
results of the Automated Recovery and force the unit back to its last commanded setting.