Wegener UNITY 550, Руководство пользователя

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Chapter 4: Search Functions
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Table 4.3: Acquisition Mode Behavior
4.4 Acquisition Sub-Modes
The state diagram in
Figure 4.2
shows the transitions for each of the acquisition sub-modes
within the acquisition modes.
Note: [! means "not"].
Note: "Satellite Searching" is obsolete and should be considered always true in the logic
shown.
Acquisition
Mode
Description
Tracking In Tracking Mode, the unit tracks (monitors) an acquired carrier. This is the
only mode in which the unit can provide video, audio, and/or aux data. The unit
will move to the Header Search mode if, (1) an invalid network header is
detected in the
COMPEL
network stream, or (2) the time since the last valid
network header was detected exceeds the No COMPEL Time-out (#4 in
SETTIMEOUT command).
Fade The purpose for this mode is to reacquire a faded carrier (caused by rain, sun-
outs, etc.). The unit allows the receiver daughter-card to automatically re-
acquire the carrier on its own using a restricted search algorithm. This mode is
vacated for the Installation mode after the Fade Timeout (#1 in SETTIMEOUT
command).
Installation While in Installation mode, the unit continually performs an installation-type
acquisition on the requested carrier. Installation-type acquisitions cover a ~+/-2
MHz range, and should occur in under 30 seconds. This mode is generally
used at power up and for all user-requested acquisitions. This mode is vacated
for the Carrier Search mode after the Installation Timeout (#2 in the
SETTIMEOUT command).
Carrier Search While in Carrier Search mode, the IRD resorts to the Settings Table for finding
a carrier. The IRD continually moves down the table performing one complete
installation-type acquisition on each valid entry in the table, including the last-
acquired and last-requested entries. Each individual search lasts one minute.
After the last entry is searched, the unit repeats the search from the top of the
table. This mode is vacated only if a carrier is successfully acquired, OR if a
local user issues a tuning command. However, after expiration of the Carrier
Search Timeout (#3 in the SETTIMEOUT command), if Local Control had been
previously disabled, then it is re-enabled.
Header Search The Header Search mode is identical to Carrier Search mode, except that the
unit is looking for a carrier with valid
COMPEL network headers present. If a
carrier is encountered, the unit will wait the amount of time given by the
Header Seek Timeout (#5 in the SETTIMOUT command) before moving on to
try other carriers in the Settings Table. This mode is vacated only if a carrier is
successfully acquired and a valid header is received, OR if a local user issues
a tuning command. However, after expiration of the Header Search Timeout
(#6 in the SETTIMEOUT command), if Local Control had been previously
disabled, then it is re-enabled.