Sea Tel ST88-21 C/Ku-Band TVRO, Installation And Operation Manual

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Setup – Searching ST88-21 C/Ku-Band TVRO
9-2
9.1.2. Inclined Orbit Search Pattern
Some older satellites, in order to save fuel to keep them exactly positioned over the Equator, are in an
inclined geosynchronous orbit. The satellite remains geosynchronous but is no longer geostationary. From a
fixed observation point on Earth, it would appear to trace out a figure-eight with lobes oriented north-
southward once every twenty-four hours. The north-south excursions of the satellite may be too far off the
center point for a default box search pattern to find that satellite at all times during the 24 hour period.
You can configure the ACU to do a special search pattern for a satellite that is in an inclined orbit by using the
following settings:
SEARCH INC
- set to the default value for the frequency band that your antenna model is currently
being used for (typically 15 counts).
SEARCH LIMIT – leave this set to the default value for your antenna model.
SEARCH DELAY
– default, or any number of seconds from 1-255 that you would prefer that the
ACU wait before starting an automatic search.
SWEEP INC – set to 192 if your antenna is a Series 04 or Series 06 or Series 09. Set to 193 if your
antenna is a Series 97, Series 00 or Series 07. This parameter sets the sweep increment (shown in
the graphic above) to be +/- 8.0 degrees above/below the satellite arc.
GYRO TYPE – must NOT be set to zero.
SAT REF
mode – It is normally
OFF
as long as you have good gyro compass input. It
MUST
be
OFF
when the elevation angle is greater than 75 degrees. It
Must
be
ON
if you are experiencing
frequent, or constant, gyro read errors (error code 0001).
Target the desired satellite longitude value but include an odd tenths digit (ie if you desire to target inclined
satellite 186.0 W you would key in SAT 186.1 W for the ACU to do an inclined search). The Antenna Control
Unit calculates the Azimuth, Elevation and Polarization values it will target the antenna to.
Initially the antenna will go to a calculated position that is half of SWEEP INCR degrees above, and
perpendicular to, the satellite arc (along the same angle as polarization for the desired satellite). This position
is the “Start” of the search pattern in the graphic above. Then the antenna will drive down along the
polarization angle SWEEP INCR degrees, step one Search Increment to the right (parallel to the satellite arc),
search up along the polarization angle SWEEP INCR degrees, step two Search Increments to the left, search
down, etc expanding out in the search pattern until Search Limit is reached. When the end of the search
pattern is reached, the ACU will retarget the antenna to the calculated Azimuth and Elevation point.
If the desired signal is found (AND network lock is achieved in the satellite modem) at this position, or
anywhere within the search pattern, the ACU will terminate search and go into Tracking mode. If the desired
signal is not found the ACU will wait SEARCH DELAY, then target the antenna to start point shown in the
graphic above and begin the search pattern again. This cycle will repeat until the desired satellite signal is
found or the operator intervenes.