Wegener Communications UNITY 4600 - Manual (Page 31)

U NITY 4600 U SER ’ S M ANUAL
www.wegener.com 23 800032-01 Rev.F
Chapter 3 Operation
This chapter provides an overview of Unity 4600 operation, details of controls and indica-
tors, 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 multi-
plexer 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
U4600 also decompresses the components of a selected pro-
gram 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.
Figure 3.1 presents a log-
ical block diagram of U4600 operation.
Available outputs from the U4600 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 U4600 attempts to resume normal opera-
tion through a process called Automated Recovery. Referring to an internal, non-volatile list
of "presets", the
U4600 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 oper-
ation or is halted by local user command. If successful with a preset, the settings in that pre-
set 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 set-
ting.