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Tracking problem with 9m dish
6th Jul, 2017 at 11:34am
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We replaced new Antenna control unit for 9.3 meter antenna and found Antenna control unit some times works for over a week without any issues and occasionally goes out of track  two or three times per week.

Help please.
  

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Re: Tracking problem with 9m dish
Reply #1 - 6th Jul, 2017 at 12:19pm
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There are very many possible reasons, all except one will be not the problem, so difficult to troubleshoot.

Here are some thoughts from me:

The beacon signal goes very low due to rain (e.g. Ku band) and the tracking stops and fails to find satellite afterwards. Maybe learned orbit or program track would work better.
The beacon signal goes very low due intermittent LNB or bad cable connection. Check alarms work.
The satellite is manoeuvred and goes the wrong way from what the tracking controller expects, assuming it has learned the orbit. Review configuration – time delay to recheck peak up.
Interference either from satellites or local terrestrial. An abnormally large signal at some other frequency could cause overload, gain compression and intermodulation interference.
The beacon level into the receiver should be within the designed range. For example if the beacon receiver is designed for beacon inputs at levels 0 dBm to –30 dBm a good clear sky level to set, using prior gain adjustment or attenuator, would be -8 dBm.  The total power into the receiver must also be less than what it can tolerate.
The variations in beacon level must be linear.  If the antenna is mis-pointed by 5 dB the level must go down by 5 dB.  If the LNB or downconverter and is overloaded and near saturation the shape of the top of the main beam looks rounded and wrong. A fixed attenuator (10, 20 or 30 dB) in the cable to the tracking receiver input may be needed.  The tracking controller software expects a normal shaped top to the main beam.
You could be peaked up on the first sidelobe. Top right or top left, lower right or lower left.  These quadrant point on the ring look like the main beam if you don’t explore much wider.  If you manually peak the dish, sweep widely either way in azimuth and elevation so you can definitely see both first sidelobes and the one big main beam in the centre. You can plot this pattern on an analyser set to zero span and 60 seconds sweep. The first sidelobes should both be about the same level and about 10 to 20 dB below the main beam level. See http://www.satsig.net/sub-reflector-alignment.htm. ; If you see two apparent “main beams” side by side, then you are sweeping either side of the null between the main beam and the first sidelobe, above or at the side of the real main beam. Put the dish in the middle of the null between the two supposed “main beams”, then move at right angles to find the truth.

The tracking controller will have a very complicated configuration and multiple modes.  Make a record of everything in the configuration first.  If you have the old tracking controller, extract all its configuration details also and write them down.
Compare the old and new configurations. Reading the handbook is important and maybe get help from the manufacturer.
An important setting is the step size, which may be measured in mS of motor run time. This is unique to your motors, gearboxes, actuators, dish diameter and frequency. When in step track mode the antenna may move up to 4 steps in one direction, and use the 4 measurements to determine which way to go to improve matters and how far to go. It may be useful to watch the motor shaft and actuators moving to try to understand what is going on.

The actuator system, motors and gearboxes need to be lubricated and run freely both ways. Some backlash can be expected.

The az/el resolvers or encoders should similarly work reliably. If you manually drive the dish, the readouts should change steadily with no stopping, no jumps and no random spurious readouts. Backlash will mean different readouts according to which direction you approach the same actual position.

If anyone has ideas please add below.
  

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chriswlan
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Re: Tracking problem with 9m dish
Reply #2 - 5th Aug, 2017 at 6:24pm
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I've never even seen any of those things, but if there is some old flexible cables, that constantly move with the system, and perhaps with the wind, some of the cable wires might be breaking internally with nothing showing. Very intermittent and very hard to trace.
  
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Nimrod Kapon - Oasis Networks
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Re: Tracking problem with 9m dish
Reply #3 - 6th Aug, 2017 at 6:37am
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Is it a station kept satellite or inclined orbit?

For I.O satellite, some additional configuration is required on the controller...
  
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