sat-nms ACUs with the tracking function installed give access to the tracking mode and the fine tune parameter which lets you adapt the tracking to the individual requirements of the antenna and the satellite you are tracking to. ACUs without tracking function show an empty page at this place.

General Settings

• Tracking mode — The tracking mode parameter selects the tracking method, the ACU actually uses. Possible selection are:
  • OFF — No tracking is performed.
  • STEP — Step track mode. In regular intervals, the antenna performs small search steps to optimize the pointing. Chapter ‘8.3.0 Step Track’ gives more information about this mode.
  • STEP-TLE — The antenna tries to optimize its pointing like in STEP mode. If the level of the received signal is too low for this optimization, the antenna moves along the path calculated from a TLE parameter set instead.
  • STEP-I11 — The antenna tries to optimize its pointing like in STEP mode. If the level of the received signal is too low for this optimization, the antenna moves along the path calculated from an Intelsat 11 parameter set instead.
  • MEMORY — The antenna tries to optimize its pointing like in STEP mode. If the level of the received signal is too low for this optimization, the antenna moves to the position it had exactly one siderian day before.
  • ADAPTIVE — The adaptive tracking mode works the same way as step track, but it additionally is capable to predict the satellite’s position when the beacon reception fails. It computes mathematical models of the satellites motion from the step track results recorded over a certain time. Details about this tracking mode are given in chapter ‘8.4.0 Adaptive Tracking’ .
  • PROGRAM — The program tracking mode is different from the modes above. The ACU moves the antenna along a path which is described in a data file. No beacon reception is required for this. You have to create such a data file and copy it with FTP to the ACU before you can use this mode. SatService GmbH provides a PC software which lets you easily create data files for program track from commonly used ephemeris data sets for geostationary satellites. Chapter ‘8.5.0 Program Tracking’ describes this tracking mode more detailed.
  • TLE — The antenna moves along a path calculated from a TLE ephemeris data set. There are no optimization steps and no receive signal is required for such an optimization.
  • I11 — The antenna moves along a path calculated from an Intelsat 11 parameter data set. There are no optimization steps and no receive signal is required for such an optimization.
• Initial pointing mode — The initial pointing mode specifies how the antenna finds its initial position before it starts the tracking mode selected with the setting above. This parameter only has an effect, when a target memory gets recalled. Changing the initial pointing mode does not re-position the antenna. Possible selection are:
  • STORED-POSTION — The antenna moves to the Az/El/Pol angles stored for the particular satellite. After this position has been reached, the tracking selected by the ‘tracking mode’ is started.
  • ORBIT — The antenna’s Az/El/Pol angles are calculated from the satellite’s orbit position stored in the recalled target memory. The ‘target azimuth offset’ and ‘target elevation offset’ values described later on this page are added to the calculated angled before they are applied. After the commanded position has been reached, the tracking selected by the ‘tracking mode’ is started.
  • TLE — The antenna’s Az/El angles are calculated from the TLE data set selected in the recalled target memory. The ‘target azimuth offset’ and ‘target elevation offset’ values described later on this page are added to the calculated angled before they are applied. The Pol angle is set to its stored position in this mode. After the commanded position has been reached, the tracking selected by the ‘tracking mode’ is started.
  • I11 — The antenna’s Az/El angles are calculated from the I11 data set selected in the recalled target memory. The ‘target azimuth offset’ and ‘target elevation offset’ values described later on this page are added to the calculated angled before they are applied. The Pol angle is set to its stored position in this mode. After the commanded position has been reached, the tracking selected by the ‘tracking mode’ is started.
  • MODEL — The antenna’s Az/El angles are calculated from the adaptive tracking model stored with the recalled target memory. The Pol angle is set to its stored position in this mode. After the commanded position has been reached, the tracking selected by the ‘tracking mode’ is started.
• Tracking cycle time — The cycle time specifies how often the ACU shall perform a step track cycle. The value is to be entered in seconds. In fact, the parameter does not specify a cycle time but the sleep time between two tracking cycles. This means, the true cycle time is the time the ACU needs to perform one step track cycle plus the time entered here. 300 seconds (5 minutes) is a good starting value for this parameter. Inclined orbit satellites probably will require a shorter cycle time, very stable satellites can be perfectly tracked with one step track cycle every 15 minutes (900 seconds). The maximum cycle time accepted by the ACU is 1638 seconds. This parameter is also used so specify how often the antenna position shall be moved in the PROGRAM, I11 and TLE tracking modes.
• Polarization prediction — Sets the polarization prediction mode to be used during tracking. The following modes van be selected:
  • OFF — No polarization prediction is done. The polarization angle is set once when a target memory is recalled and stays at this value while the antenna tracks.
  • ON — The polarization angle is calculated from the satellite’s position and it’s inclination angle. With TLE ot I11 tracking, these values are taken from the ephemerid data evaluation. With other tracking modes the polarization angle is calculated from the satelite’s nominal orbit position and the inclination value set with the target parameters. Te polarization angle gets updated with each tracking step in this mode.
  • ADAPTIVE — This mode works very much like ‘ON’, but with step track based tracking modes the values for the satelite’s orbit position and inclination are re-calculated from the recorded tracking data every three hours. This does not change the values of these parameters stored with the target memory, but the actual polarization angle calculation the optimized values are used instead of the stored ones.
• Target orbit position — The nominal orbit position of the satellite (°E). This value is used for the initial pointing of the antenna if the ‘initial pointing mode’ is set to ‘ORBIT’.
• Inclination — The satellite’s inclination used for the polarization prediction calculation.
• Max. prediction age — If the epoch of a TLE or I11 parameter set which is actually in use (‘TLE’ or ‘I11’ tracking modes) is older than the time specified here, a TLE-OUTDATED or I11-OUTDATED fault is raised and the antenna does not move with this and following tracking steps. The same applies in ADAPTIVE tracking mode if the antenna follows its calculated model without successful steptrack for a longer time than specified here.

Steptrack Parameters

• Tracking step size — The tracking step size is a very important parameter for the performance of the tracking. It defines the size of every depointing step, the ACU makes in order to find out where the optimal antenna pointing is. Setting too high values will cause significant signal degradations during the step track cycle because the antenna moves a too large amount away from the satellite. Setting the value too small will let the beacon level jitter mask the level differences caused by the test steps, the antenna will not track the satellite properly.The step size is specified as a percentage of the antenna’s half 3dB beamwidth. The ACU calculates the beamwidth from the antenna diameter and the beacon frequency. Expressing the step size in this relative way keeps the value in the same range, regardless of the type of antenna. The recommended value for this parameter is 15-20%. You may want to start with 20% and try to reduce down to 15% if the signal degradation during tracking becomes too high.The tracking step size is a common parameter for both axes. If both axes behave differently, you can tweak the antenna diameter settings in the setup. Specifying a larger diameter makes the ACU using a smaller step size for this axis.If the tracking step seems to be completely out of range, you should check if the beacon frequency is set properly. The frequency must be the true receive frequency at the antenna, entered in MHz, not an L-band frequency or other IF.

• Beacon frequency — This parameter tells the ACU the frequency of the beacon signal to be used for tracking. The ACU calculates the antenna beam width from this frequency and the antenna diameter configured at the setup page. The value has to be entered as true receive frequency, no L-band or other IF frequency. When used with a SatService beacon receiver, the ACU automatically reads the beacon frequency at the start of each tracking cycle from the receiver. Any value entered here will be overwritten in this case. The beacon frequency entered here never sets the frequency at the receiver, neither with a SatService receiver nor with a third party device!

• Level offset — Principally there are two ways to display a beacon receive level: Either as an absolute level in dBm as reported by the receiver or as a relative level with ‘0dB’ signalling the nominal level at clear sky conditions. The latter gives an easy measure for any degradation of the receive level.The parameter ‘Level offset’ lets you calibrate the absolute reading of the beacon receiver to the relative level. You may either enter a value to shift the reading by this offset or you may click to the ‘calc.’ link beside this parameter to set the offset to the actual absolute level reading, making the actual level being 0dB relative.

• Level threshold — If the relative beacon level falls below this threshold value, the ACU does not perform a step track cycle. If the level falls below the threshold during the steptrack cycle, the cycle gets aborted. If the ADAPTIVE tracking is enabled and there is enough data in the tracking memory, the ACU computes a mathematical model from the stored data and predicts the antenna pointing position from the extrapolation of the model. Analogously the antenna is moved to the actual TLE it I11 position in such a case if the ‘STEP-TLE’ or ‘STEP-I11’ mode is selected. If the tracking mode is set to ‘STEP’, the ACU leaves the antenna where it is if the beacon level drops below the limit.

  Adjusting the threshold level that adaptive tracking is switched as expected must be done carefully and may require some iterations, specially if the beacon is received with a low C/N.

  A good starting value for the threshold is 10 dB below the nominal receive level or 2 dB above the noise floor the beacon receiver sees with a depointed antenna, whatever value is higher. As mentioned above, the level threshold refers to the relative beacon level, not to the absolute level reading.

  To turn off the monitoring of the beacon level (this in fact inhibits the adaptive tracking), simply set the threshold the a very low value (e.g. -99 dBm)

• AZ Maximum model type / EL Maximum model type — These settings let you limit the adaptive model to a simpler one, the ACU would choose by itself. The maximum model type can be set individually for each axis. Normally you will set both axes to ‘LARGE’, which leaves the model selection fully to the ACU’s internal selection algorithms.In cases where the ACU seems to be too ‘optimistic’ about the quality of the step track results, the maximum model on one or both axes may be limited to a more simple and more noise-resistant model. Specially inclined orbit satellites which are located close to the longitude of the antenna’s geodetic location may require this limitation for the azimuth axis. With such a satellite, the elevation may move several degrees while the azimuth shows almost no motion.

• Measurement delay — During a steptrack cycle, the ACU positions the antenna to a certain offset and then measures the level. Between the moment when the antenna reached commanded position and the beacon level measurement the ACU waits some time to let the beacon level settle. The optimal delay value depends on the beacon receiver’s averaging / post detector filter setting and is a quite critical for the steptrack performance.If the delay is too short, the beacon voltage does not reach its final value, the steptrack does not properly recognize if the signal goes better or worse after a test step. If the delay is too long, the impact of fluctuation to the measured level grows and may cover the small level difference caused by the test step. With the sat-nms LBRX beacon receiver, best results are achieved if the receiver is set to 0.5 Hz post detector filter bandwidth and a measurement delay of 1500 msec.

• Recovery delay — After the ACU has done the tracking steps for the elevation axis, it waits some time before it starts tracking the azimuth axis. This is to let the beacon level settle after the final position has been found. A typical value for this parameter is 4000 msec.

• Level averaging — When measuring the beacon level, the ACU takes a number of samples and averages them. The standard value of 5 samples normally should not be changed. Larger values will slow down the ACU execution cycle.

• Retry after motor fault — When the ACU encounters a motor fault during steptrack, the tracking cycle gets aborted and the ACU shows a fault. This parameter tells the ACU how to proceed after this, with the next tracking cycle:

  • NEVER — The ACU will not try to move the antenna again. This will stop tracking until an operator will have checked the antenna motor and re-started the tracking.
  • FOREVER — The ACU try to move the antenna again with the next tracking cycle. If the antenna is really blocked, the ACU will try to move the antenna every tracking cycle. This increases the probability to keep the antenna following the satellite - even if the antenna motors show sporadic faults. But this also increases the risk to crash motors and/or spindles of the antenna.
  • ONCE — This mode offers a compromise between preserving the motors and trying to keep the antenna following the satellite. The mode ONCE allows the ACU to do exactly one retry after a motor fault, if this fills as well the ACU stops tracking

• Smoothing interval — This parameter controls the smoothing function. Setting it to zero disables smoothing. Smoothing lets the ACU point the antenna to positions evaluated from a simple model calculated from the step track peaks of the recent few hours. A detailed description of this function you find at chapter ‘8.3.3 Smoothing’

• Peak jitter threshold — If the jitter value of at least one axis exceeds this threshold, the ACU raises an ‘model fault’. If this happens three consecutive times, the ACU resets the models of both axes. Adaptive tracking will be possible not until 6 hours after this happens.During adaptive tracking, the ACU evaluates for each axis a figure called jitter. The jitter value describes standard deviation of the measured peak positions with respect to the positions calculated from the (currently selected) model. The figure is also expressed as a percentage of the antenna’s beamwidth, low values indicate, that the model ideally describes the antenna’s path. High values indicate that’s something wrong. The step track results may be to noisy at low amplitudes or the model does not fit at all. This may be the case if a satellite gets repositioned in the orbit.A typical threshold value is 20%, this will detect very early that a model does not fit to describe the satellite’s motion. If this value causes false alarms too often, you may want to raise the threshold to 50%. Setting it to 0 switches the threshold monitoring completely off.

• Spindle save mode — If set to OFF, the ACU does a step track optimization with every tracking cycle. If set to a value 1 .. 12, the ACU will insert steps where it positions the antenna following the actual ADAPTIVE model. If e.g. the spindle save mode is set to 2, the ACU will do a step track optimization in the first cycle, in the second and third cycle it skips this and moves the antenna following the actual ADAPTIVE model. This reduces the number of antenna movements and spindle wear.

• Spindle save threshold — Defines the model quality (jitter value) neccessary to replace step track optimization steps in spindle save mode. If the jitter value of one axis exceeds this value, the ACU does step track optimization steps everycle even if spindle save mode ist active.

• Model hysteresis — If set to a non-zero value, antenna movements below this threshold are suppressed whenever the antenna is controlled by an adaptive model or by ephemeris data. The value is expressed as a percentage of the half 3dB beamwidth of the antenna. You may use this parameter to reduce the number of antenna movements in these modes.

• Apply model before track — If set to ON the ACU moves the antenna to a position calculated by the actual adaptive model before it starts a steptrack optimization sequence. With inclined orbit satellites this helps to follow the satellite with minimized level degradation.

Prediction Parameters

• I11 Ephemerides — The ACU provides 99 named memory places (numbered 1..99) to store Intelsat 11 parameter sets. With this parameter you address the number of the I11 parameter set to be used with the ‘I11’ or ‘STEP-I11’ tracking modes and for the ‘I11’ initial pointing mode as well. The setting is a reference to the memory location where the I11 parameter are stored, hence, if the parameters at this location are changed the ACU automatically uses the changed parameters.
• TLE Ephemerides — The ACU provides 99 named memory places (numbered 1..99) to store TLE Ephemerides sets. With this parameter you address the number of the TLE parameter set to be used with the ‘TLE’ or ‘STEP-TLE’ tracking modes and for the ‘TLE’ initial pointing mode as well. The setting is a reference to the memory location where the TLE parameter are stored, hence, if the parameters at this location are changed the ACU automatically uses the changed parameters.
• Target azimuth offset / Target elevation offset — The offsets specified here are added to any antenna pointing which is calculated from ephemeris data or from an orbit position and also to the pointing angles read from a file in PROGRAM tracking mode. The offsets can be used to compensate for differences between measured and calculated angles, e.g. if the azimuth axis of the antenna is not exactly vertical.

Beacon Receiver Parameters

If the ACU is configured to work together with a sat-nms beacon receiver, the receiver’s settings may be remote controlled from this section of the target parameters. The beacon receiver settings are stored when a target memory is saved and and set at the beacon receiver when a target memory is recalled. Beacon receiver parameters are not available if the ACU works with a 3rd party beacon receive

• RF receive frequency — This is the receiver’s nominal receive frequency. Depending on the LO frequency settings made on the Setup page, the frequency value either is expressed as the RF receiver frequency or the L-band frequency at the receiver’s input. If the ‘22 kHz Tone’ setup parameter is configured as ‘AUTO’, changing the frequency also may switch the 22kHz modulation on the LNB power supply on or off.
• Polarization — If on the Setup page the ‘LNB voltage’ parameter is set to ‘AUTO’, the receive polarization may be set with this parameter by changing the LNB Voltage.
• Attenuation — The receiver provides a switchable input attenuator which lets you adjust the input level in 10 dB steps. This is specially useful with large Antennas pointing to a satellite which generate a high flux density. With the attenuator you may adjust the input level in order to avoid saturation effects in the receiver. All input attenuator steps are calibrated, the attenuation values are taken into account for the displayed receive level. Available attenuator settings are 0, 10, 20 and 30 dB.
• Measurement Bandwidth — The receiver provides four different measurement bandwidth filters (6, 12, 30 and 100 kHz). The 30 kHz filter is suitable for majority of cases.
• Post detector filter — The receiver’s software applies a low pass filter to the measured level values. This is much like the video filter at a spectrum analyzer. Available bandwidth settings for this filter are 0.1 to 5 Hz in 1/2/5 steps. Lower bandwidth settings make the reading more stable, reduce the fluctuation. Please keep in mind, it will take a noticeable time until the level reading settles after an input level change with a very low bandwidth setting.
• Alarm Threshold — With this parameter you set the level threshold. If the measured level falls below this value, the receiver states a receive level fault. To disable the level alarm, set the threshold to a very low value, e.g. -120 dBm.Please note, that the threshold value refers to the signal level, even if the receiver operates in a C/N measurement mode.
• C/N Noise measurement — With this parameter you select if the receiver shall perform a plain input level measurement or a C/N measurement. A description of the C/N measurement function of the receiver is given in chapter 5.3 C/N Measurement . You may select one of the following measurement modes:
  • OFF — The receiver performs a plain level measurement. The Readings page shows the input level in dBm.
  • C/N — The receiver measures the signal / noise ratio. The Readings page shows the C/N in dB.
  • C/N0 — Like the C/N mode, but the receiver normalizes the C/N value to 1 Hz measurement bandwidth. The Readings page shows the C/N0 in dBHz.
• Frequency Tracking — This parameter switches the the frequency tracking facility of the receiver ON or OFF. A description of the frequency tracking facility is given in chapter 5.4 Frequency Tracking .
• Noise Measurement Frequency — With this parameter you specify the frequency at which the receiver shall measure the noise level at a certain interval. Like with the receive frequency, the LO frequency settings made at the Setup page are taken into account also for this frequency value.To get reasonable results with a C/N measurement, you should consider the following:
  1. The receiver does not change the LNB frequency band setting when it switches from the level measurement to the noise measurement. The LNB probably would change it’s gain in this case. The noise measurement frequency hence must be in the same frequency band as the receive frequency.
  2. Measuring the noise level at the band edge may falsify the result due to the LNB’s band filter. The measured noise level may be too low in this case.
  3. You should verify with a spectrum analyzer, that no signal disturbs the noise measurement at the selected frequency.
• Frequency Tracking Interval — This parameter sets the interval on which the frequency tracking procedure operates. The value is in seconds. Recommended settings are 15 seconds to tune the receiver quickly to a frequency you do not know precisely. For normal operation a frequency tracking interval of one hour (3600 secs) is recommended.
• Noise Measurement Interval — This parameter defines the interval at which the receiver inserts noise measurements in the C/N modes. The time is specified in seconds. 3600 secs being one hour is a suitable setting in most cases.
• Frequency Tracking width — With this setting you limit the frequency offset the frequency tracking procedure may apply to the nominal frequency. The frequency tracking never tunes the receiver to a frequency outside the nominal frequency +/- this value, a frequency track fault is generated if the tracked frequency reaches the limit.
• Signal search enable — Setting this parameter to ON enables the automatic signal search function. With signal search enabled, the receiver searches the signal within the frequency tracking range when the signal ist lost. Chapter 5.5 Signal search describes this function more detailed. ‘SEARCH NOW’ starts a search scan immediately, regardless of the enable setting.
• Analog output offset — The beacon level shown as 0V at the analog output.
• Signal search delay — This parameter defines the time, the receiver waits after the signal was lost until a search scan ist started. The valid range of this parameter is 0 .. 600 seconds.
• Analog output scale — The analog output scale (V/dB)
• Spectrum Compensation — With this parameter set to ‘OFF’, the receiver’s level reading is calibrated for a C/W signal. By selecting a modulation type for this parameter, the level display gets compensated for the selected modulation type.

CLEAR TRACKING MEMORY

Clicking to this mark clears the tracking memory. You should do this when you start to track a new satellite. Clearing the tracking memory about half an hour after tracking started significantly improves the quality of the first adaptive tracking model which will be evaluated after 6 hours of tracking. This is because the model does not get disturbed by the first search steps the antenna does until the optimal pointing to the satellite is found.

Please refer to chapter 8.3 Steptrack , 8.4 Adaptive Tracking and 8.5 Program Tracking for more detailed informations about the tracking algorithms.