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Help me: Dish pointing and alignment

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Feb 6th, 2007 at 5:27pm  
hello,
i have troubles with my dish .
i live in egypt and i have troubles with satellite astra,the signal strength become high at midday and at night it become weak and even cannot recieve saignal (bad signal ).
here is the info. about my system
prime focus dish 180cm .
fugi lnb .
i hope somebody can help me.
regards
habib2006
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« Last Edit: Feb 18th, 2007 at 11:48am by Admin1 »  
 
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Reply #1 - Feb 9th, 2007 at 11:29pm  
i am sorry i put this thread in the wrong place .
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Reply #2 - Feb 9th, 2007 at 11:54pm  
Yours sounds like a Center of Box issue. That is; as the earth wobbles on its axis, the satellite "appears" to move back and forth every 12 hours. This back and forth movement is consistent, the pattern of which is considered "the box". It's best to have your dish aligned with the  center of this box, rather than at one end. If not, you'll experience a 12 hour cycle of rising and falling signal strengths.

//greg//
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Reply #3 - Feb 14th, 2007 at 2:27pm  
You can replace LNB with PLL, maybe you have problem with noise temperature
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Eric Johnston
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Reply #4 - Feb 14th, 2007 at 4:46pm  
If the earth station dish is mispointed, so that the satellite is on the side of the main beam, then small satellite movements (+/- 0.1 deg) will cause level changes over each day.   This problem is most noticable on larger Ku band dishes, whose main beam is narrow.

In the outer regions of the downlink beam coverage  the levels vary rapidly with distance, also with slight satellite downlink beam mispointing.  Trying to receive satellite signals when you are not really in the intended beam coverage pattern is uncertain, even if you have a large dish.   If you are more than 6 dB down from the beam peak expect variations.  Have a look at the downlink beam pattern.

If your reception is marginal in clear sky conditions expect to always lose the signal in slightly degraded conditions.  Digital carriers quicky transition from working OK to failed, so it is important to get the best possible signal in clear sky conditions.

For the reception of wide, high symbol rate carriers as used for satellite TV, high stability, low phase noise PLL type LNBs are not required.  Cheap DRO types will do.  You need the PLL type LNBs for small narrow, low symbol rate carriers and for high efficiency modulation techniques like 8-QAM and 16-QAM modulation.

Moisture on the feed window and moisture inside the LNB waveguide will attenuate the signals and increase noise temperature.  Keeping it dry is important.   Similarly for the cable.  Dampness sucked in at night tends to cause permanent corrosion and high losses.

If an LNB suddenly stops working at a particular temperature and returns again when warmed up then it is faulty.

Best regards, Eric.
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Reply #5 - Feb 17th, 2007 at 2:21pm  
first of all thanks for your replaies.
ohhhh , i sufferd alot for this problem and till now i still tries to get the best signals from these satellites .
although i had thought of (center of box )issue ,but i can not get the schadule of the satellite so as to allign my dish when it is at the center of the box .
as i have a motorised system i have to align my dish carfully to get high signals on all satellites which i can receive .
another question to be asked : if my lnb is not at the focus exactly ,does this will affect signal recepton of weak signals ,and to what extent ?
regards
habib2006
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Eric Johnston
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Reply #6 - Feb 17th, 2007 at 3:29pm  
With a 1.8m dish the variation during the day suggests it is mispointed and that the satelite is moving up and down the side of the main beam.  When is is bad try pushing the dish slightly to see if there is an improvement - and note which way.

If you have a motorised polar mount dish then the most likely problem is that the antenna is mispointed for some satellites.  They are in a curved line across the sky.  The line of movement that your mount generates should ideally match this line all across the sky, to an accuracy of about 0.15 deg.  This is not at all easy to set up.

There 3 errors possible (main polar angle, small downward tilt angle and the due south setting), which may cause various combinations of:
Too high elevation all across
Too low  elevation all across
Too low  elevation at both sides
Too far left at one side, too far left at the other
Too far left at one side, too far right at the other
Too low elevation in middle, OK either side
etc.

An alignment error of 0.5 deg with a 1.8m dish means your signal will be -3 dB down on average.  Over a day with +/-0.1 deg satellite movement your signal will vary from -2 to -4.5 dB.   If you were pointed perfectly the daily satellite movement of +/-0.1 deg would produce no detectable reduction at all (< 0.2 dB)

The best I can suggest is check your polar mount main axis angle and small downward tilt angle very carefully with an inclinometer, thread and weight etc.  Optimise  for the nearest satellite you can detect around due south.  Alter the main clamp due south direction if needed.

Before you start swing the dish fully from one horizon to the other and write down the signal quality for representative satellites dwon near the horizon at each side, also about half way up the sky and also in the centre near due south.

There is some discussion about possible adjustments here http://www.satsig.net/polmount.htm

This calculator gives an output of the sideways polar mount motor drive angles for a polar mount.  It may help.  Drag the map sideways until Egypt is visible. The towns are all marked so you will be able to find your house perhaps! Press + to magnify.

I must warn however that aliging a large (1.8m) polar mount dish is far from easy.
wxw
Best regards, Eric.
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Reply #7 - Feb 17th, 2007 at 11:45pm  
Quote:
although i had thought of (center of box )issue ,but i can not get the schadule of the satellite so as to allign my dish when it is at the center of the box .
as i have a motorised system i have to align my dish carfully to get high signals on all satellites which i can receive .

No manner of adjusting Az/El/Pol will achieve accurate tracking over the orbital arc if the mounting pole is not plumb. I suggest you start simple, get a spirit level. Make sure the polemount is perfectly vertical on all sides. If you're off even half a bubble, it will affect the tracking.

Quote:
another question to be asked : if my lnb is not at the focus exactly ,does this will affect signal recepton of weak signals ,and to what extent ?


I'm not sure of your meaning here. Please explain "not at the focus exactly".

//greg//
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Reply #8 - Jul 17th, 2007 at 7:04pm  
Hi!
Can anybody help me with my dish setup?
I'm at 34 deg lat. and -117 deg long.  I need to point my dish at Intelsat 8.  I'm using a dish 500 with twin LNB.  Will this work?

Thanks!
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Reply #9 - Jul 17th, 2007 at 8:28pm  
Quote:
  Will this work?

Work for what?

Most folks with that particular hardware use it for DishNetwork TV. I'm personally unaware of any Dish service from that location. The satellite formerly known as IA8 by the way - is now called Galaxy 28

//greg//
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