2 program_track, 3 intelli-search, 2 program_track 4.2.3 intelli-search – Research Concepts RC2000C User Manual

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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

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