Service manual

RC2000 Service Manual Chapter 4 Common RC2000 Questions 27
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The limit error occurs when the antenna controller is tracking an inclined orbit satellite and one of the
antenna azimuth or elevation limits is reached. For the RC2000B models this can occur either when then
controller is in the Search sub-mode performing a search or when the antenna is being peaked in either
the Step Track or Program Track sub-modes. For the RC2000C the search is truncated at the antenna
limits so this error can only occur when an antenna peakup is in progress.
If this error occurs while peaking the antenna there is really nothing else to do but reset the antenna limits
or reconfigure the actuators to allow greater movement of the antenna. For the RC2000B and RC2000C
POLAR models the procedure for setting up the mount is described in the addendum to the manual
entitled 'Addendum - RC2000C POLAR and RC2000B POLAR Antenna Controller'.
If the error occurs while the Search is in progress the search window may be either too large or not
centered properly. The apparent motion of an inclined orbit satellite is a narrow figure eight shaped
pattern. The height of the figure eight (in degrees - as seen from the surface of the earth) is approximately
2.4 times the inclination of the satellite's orbital plane to the earth's equatorial plane (i.e. for a satellite with
a four degree inclination the height of the figure eight is approximately 10 degrees). The center of the
figure eight will be located on the Clarke belt (where the geostationary satellites are located). The
controller calculates the height of the figure eight based on the satellite inclination specified by the user in
SETUP mode.
If the controller is experiencing Limit errors while searching make sure that the inclination specified via
SETUP mode is not too large. Note that the inclination of an inclined orbit satellite's orbit increases by
approximately 0.9 degree per year.
The width of the controller's search region is controlled by the Azim Search Scale Factor CONFIG mode
item (in the RC2000B) or the Search Width CONFIG mode item (in the RC2000C). The nominal value of
this item is either 3 or 5. If the search window is too wide an adjacent satellite may be 'found' during a
search. Generally the value of this item can be reduced to 1 or 2 without any negative effects.
The center of the figure eight for POLAR trackers is the Geo Position Count specified by the user in
CONFIG mode. For the RC2000B AZ/EL the center of the figure eight is calculated based on the positions
of geostationary satellites in the vicinity of the inclined orbit satellite. ALWAYS VERIFY THE
LONGITUDE VALUES ASSIGNED TO GEOSTATIONARY SATELLITES.
4.5 Gaps in the Program Track Table
A peakup will not occur if there is no signal strength (as defined by the K/L or C Band Threshold CONFIG
mode items). If the transponder on the satellite is down at the sidereal times which correspond to a given
track table entry a peakup will not occur and no data will be entered into the track table.
Another event can cause gaps in the track table. To see this it is necessary to know what triggers peakups
when the STEP track sub-mode is active. When the STEP track sub-mode is active, two events can
cause the controller to initiate a peaking operation.
The first event is if the sidereal time equals a time which corresponds to one of the 48 points in the track
table. These sidereal times are: N * 86164 / 48 where N = 0.47. The current sidereal time can be viewed
via the TRAK Menu described in the manual.
The second event which can trigger a peaking operation is a bit difficult to understand. The controller
remembers the time when the last peaking operation has occurred. The controller also knows the size of
the antenna and the frequency of operation. This allows the controller to calculate the antenna's radiation
(or gain) pattern which is a relationship between signal loss and the angle from antenna boresight. The
controller also knows the inclination of the satellite (this is obtained when the track is initiated via SETUP
mode). By knowing the inclination of the satellite the controller can calculate the angular velocity of the
satellite as seen by the controller when that angular velocity of the satellite is at its greatest (i.e. when the