Research Concepts RC2000C - Manual (Page 34)

26 RC2000C Az/El Tracking Antenna Controller Chapter 4 Inclined Orbit Satellites
Research Concepts, Inc. • 5420 Martindale Road • Shawnee, Kansas • 66218-9680 • USA www.researchconcepts.com
SEARCH..receives control if the satellite signal is lost.
ERROR..receives control if any error is encountered.
4.2.2 PROGRAM_TRACK
When the PROGRAM_TRACK submode is active, the controller smoothly positions the antenna to
azimuth and elevation positions derived from the track table, regardless of whether a satellite signal is
present or not. The track table holds a map of the satellite's apparent motion as a function of sidereal
time. The controller performs a linear interpolation between adjacent track table entries to determine
the correct antenna position.
In PROGRAM_TRACK submode antenna movement occurs whenever the controller calculates that the
error between the antenna's current position and the antenna's proper position as determined from the
track table exceeds Max Track Error tenths of a dB. To determine the error between the current and
calculated antenna position, the controller calculates the antenna beamwidth based on the Antenna
Size and the frequency Band. If the Max Track Error parameter is decreased in value, the antenna
pointing error will be less, but the antenna will move more often, which increases wear on the antenna
actuators.
The PROGRAM_TRACK submode also periodically performs peakups (similar to STEP_TRACK
submode) to check the accuracy of track table entries. If the discrepancy between the peakup position
and the position stored in the track table is greater than that specified by the Max Track Error
parameter, the update flag for each entry in the track table is set TRUE. The frequency at which these
track table accuracy checks occur is determined by the Update Check parameter. The default Update
Check interval is 33 hours, but can be changed by the user to any value in the range of 1 to 999 hours
(via the TRACK MENU system).
If the current sidereal time reaches a value that corresponds to an entry in the track table whose update
flag is set TRUE, and the current signal strength level indicates that a satellite signal is present, a
peakup will occur, the track table entry will be updated, and the track table update flag is reset FALSE.
If the satellite signal is not present the update flag remains set TRUE and the system will try again in 23
hours, 56 minutes, and 4 seconds. The user can view the contents of each track table entry and
examine the present state of the update flag. In addition the user can invoke the Force Update or Reset
Update functions to force the update flag for each entry in the track table to be either set TRUE or reset
FALSE, respectively. These functions are accessible via the TRACK MENU system, which is described
in more detail in section 5.4.5.
The PROGRAM_TRACK submode will pass control to the other TRACK mode submodes under the
following circumstances:
STEP_TRACK..receives control when the current sidereal time reaches a value for which there
are no valid track table entries and a valid satellite signal is present.
SEARCH..receives control when the current sidereal time reaches a value for which there are
no valid track table entries and a valid satellite signal is not present.
ERROR..receives control when any error is encountered.
4.2.3 Intelli-Search
The SEARCH submode receives control whenever the satellite signal is lost and the track table does
not contain antenna azimuth and elevation position data for the current sidereal time. Whenever the
SEARCH submode is active the controller periodically performs a search over the region where the
controller has calculated that the satellite will be found. The Intelli-Search algorithm determines the
extent of the search region based on the Satellite Longitude, the Antenna Latitude and Antenna
Longitude, the antenna beamwidth (as calculated from the Antenna Size and frequency Band), and the
Elev Constant and Azim Constant Scale Factors.
The Azim Constant and Elev Constant scale factors refer to the mapping of antenna azimuth and
elevation position counts to antenna azimuth and elevation angles, respectively. The elevation scale