Research Concepts RC2000C - Manual (Page 47)

RC2000C Az/El Tracking Antenna Controller Chapter 4 Inclined Orbit Satellites 39
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Please review the description of TRACK mode in chapter 5 for a complete explanation of each of the
TRACK mode submodes and the TRACK mode menu system. Every field of every display screen is
described in that section.
4.4.5 Tracking Problems
This section discusses problems that can occur while tracking an inclined orbit satellite. TRACK mode
contains an ERROR submode, which displays an error message when it is active. Chapter 7 discusses
all of the possible errors that can occur. This section discusses the more common problems.
The LIMIT error occurs when an antenna limit (either azimuth or elevation) is encountered when
tracking an inclined orbit satellite. This error will only occur while the STEP TRACK or PROGRAM
TRACK submodes are active. The SEARCH submode will not attempt to move outside of the azimuth
or elevation limits. This error generally means that the azimuth or elevation (usually elevation) limits are
not set wide enough.
A PEAK LIMIT error indicates that the controller had to move the antenna too far during a STEP TRACK
peaking operation. The maximum movement of the antenna from the starting position for a STEP
TRACK operation is limited. This is to prevent the antenna from peaking up on an adjacent satellite.
This problem can be caused by a number of situations:
1. Specifying too large of an antenna diameter, or specifying Ku band when tracking a C band
satellite. These cause the controller to calculate too narrow of an antenna beamwidth. This
beamwidth is used to determine the maximum allowable movement from the starting position for a
STEP TRACK operation.
2. Specifying too small of a satellite inclination. In STEP TRACK mode, the controller performs
peakups often enough to avoid exceeding the maximum antenna pointing error specified by the
Max Track Error CONFIG mode item. If the specified satellite inclination is too small, the peakups
will not occur often enough, and the antenna may move far enough during a peakup to trigger the
PEAK LIMIT error.
3. The C Band AGC Threshold or the K/L Band AGC Threshold is set too low. If the threshold values
are set too low, when the transponder powers down, the AGC signal of the receiver may be above
the threshold when the antenna is looking at noise. In this case the controller would mistakenly
assume that the satellite signal is present, and attempt to peak up on the noise.
4. If the error occurs during a peakup operation while the PROGRAM TRACK sub-mode is active, it
may be that the Update Check Interval TRACK mode MENU item is set too large.
5. There may not be a sufficient number of position counts per degree of antenna movement about
one of the antenna axis. The controller cannot move less than one count. If a move of less than
one count is specified the antenna will round the step size up to one count. Note that all systems
will have one count of play or looseness in the antenna - see the next section. A good rule of thumb
is that there should be 10 position counts over the antenna’s 3-dB beamwidth for each axis.
6. Play or looseness in the mount can cause many problems. The user can test for play by shaking
the antenna. Another test is to see if the antenna peaks on a satellite at different count values
depending on which way the antenna approached the satellite. Here's an example. In one case
the peak is approached by jogging the antenna up and the peak occurs at 110 counts. In another
case the peak is approached by jogging the antenna down and the peak occurs at 103 counts. This
indicates that there are 7 counts of play in the system. The solution is to get rid of the play. In
some cases, increasing the Max Track Error parameter can help. In general, however, the
controller is not very tolerant of looseness in the mount.
If a linear actuator is used to drive the antenna about an axis, it usually forms one side of a triangle. As
the length of the linear actuator changes, the opposite angle varies and the pointing angle of the
antenna is changed. If the linear actuator has some play in it, the change in the antenna pointing angle
due to the play in the actuator can be minimized if the other sides of the triangle are made longer. In
some cases, the ball pivot often found on one side of the linear actuator is also loose. Anything which
can be done to tighten up the ball pivot will help.