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Problem on Seatel @ Astra 3b 23.5 E

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Bruno
Ex Member


Oct 5th, 2011 at 7:37pm  
Hi guys,

I hope somebody can help me regarding on seatel cobham stabilaize antenna.
We we're trying to test the newly purchase antenna here in Dammam.
This is the senario, when we're tracking until we got link into Astra 3B, i only stay for atleast 1hour and will track another carrier and lost our link with Astra 3B and it will never comes back but  antenna is still tracking or seaching. I notice in the spectrum analyzer that it detects other carrier.
What we did is we use another companies carrier just to determine the problem. But it happend that we have a stable link.

Assuming that balance check on ABE/Antenna and all configuration correct.

Question:
1. Does the ohter carrier could be the cause why the antenna didn't have the stable link and what would be the remedy?
2. Does it matters on the location of te antenna?


Please whoever has an idea or knowledge that can help to solve this 1 week problem is very much appreciated.


Thank you and More Power


Bruno
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Eric Johnston
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Reply #1 - Oct 5th, 2011 at 8:20pm  
If you have a single polarisation receive system, you need to track on a carrier that is on the same polarisation and in same frequency range as your wanted traffic carrier. The tracking carrier and the traffic carrier could be the same, in some scenarios.  The tracking carrier could be the satellite beacon or some other reliable carrier.

You need a tracking receiver.  This could be your traffic modem (assuming it has a suitable signal level output) or it could be some specialised tracking receiver.  If it is a specialised tracking receiver it will need tuning to suit whatever carrier you wish to track.  The signal level measurement will need calibrating and the thresholds adjusted. I believe there are two wires. One is "This is the correct carrier, i.e. locked and recognising the data content", the other is "This is the signal voltage measurement, but could be any carrier or satellite".

At installation you can tell the tracking controller that some parts of the azimuth arc are blocked (due to mast, for safely reasons etc).

A signal used for tracking must be stable in level.  Carriers that pulse (e.g.TDMA) or are only there for a few hours each day are quite unsuitable.  Carriers from uplink sites with low elevation angle are unsuitable as they vary a great deal with the weather. Good carriers are whole transponder TV carriers where the satellite has AGC to keep the output power from the satellite constant, even when the uplink is faded due to rain.  TV carriers are broad bandwidth and C/Ns are typically moderate, like 10 - 16 dB.  CW beacons are excellent but are low power and need special very narrow bandwidth tracking beacon receivers. The C/N can be very high, like 30 dB, so high quality tracking is possible.

If you are in dock, check that the dish can see the new satellite and that the path is not blocked by the funnel, masts etc. You need to tell the tracking controller the wanted satellite orbit position.  It can then calculate the elevation angle (using GPS) and swing the dish sideways to find the satellite.  Tell it the wanted downlink polarisation name also and check visually that it understands this and applies it correctly. Are you seeing the wanted polarisation on the analyser and no cross pol interference ?.

Best regards, Eric.
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