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Prodelin circular and linear

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Nov 25th, 2009 at 4:58pm  
we have prodelin 1184 (1.8 m antenna ) and 1251 (2.4m ) all with circular polarizer we have around 40 vsats.

We are going to move satellite to Linear, and than after one year we will move to circular again.

I heard that there is an option to stay with the polarizer and use linear
thanks
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Eric Johnston
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Reply #1 - Nov 25th, 2009 at 7:09pm  
Yes.

Starting in circular mode.  Undo the joint between the OMT and the polariser, turn the OMT 45 deg till the waveguides line up with the pins/slots in the polariser. Reattach. You are now in linear mode.

You could remove the polariser but there may then be weight support problems and time to lose the polariser and attachment screws etc in the meantime.

Best regards, Eric.
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« Last Edit: Nov 25th, 2009 at 10:41pm by Eric Johnston »  
 
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Reply #2 - Nov 25th, 2009 at 8:20pm  
hi Eric,
thak you for your reply,
and than,it will act as linear ?
and in order to use circular again, do i have to revert it back ?
thanks
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Eric Johnston
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Reply #3 - Nov 25th, 2009 at 10:39pm  
With the waveguides in line with the pins/slots in the polariser the polariser effect will vanish and the feed will be in linear mode.

Once you have it in linear mode note that you will have to initially set it to either horizonal or vertical and then apply a rotation adjustment angle, like virtually all Ku band systems.

To change it back to circular, undo the OMT to polariser flange and reposition, by 45 deg, so that the waveguides are +/-45 deg either way from the line of pins/slots in the polariser. One way will give clockwise, the other anticlockwise. No idea which way, so it might help to photograph how it is now so you can put it back the same way if your future circular polarisation is the same as it is now.

Best regards, Eric.
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Reply #4 - Dec 30th, 2009 at 9:31pm  
Eric,
will i have additional attenuation on the linear if i'm using the polarizer like that ?
thanks
Roee
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Eric Johnston
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Reply #5 - Dec 30th, 2009 at 10:30pm  
If you operate with the polariser included, but rotated so it has no polarising effect, then you will get some degradation due to the small attenuation in the polariser.

The effect of including the polariser might typically raise the antenna noise temperature from 24 to 28K.  Assuming a C band LNB with 51K noise temperature the antenna G/T degradation is 10log( 51+28 ) - 10log( 51+24 ) =  0.22 dB.  Hardly measurable...

Removing the polarier is technically superior, but you risk losing the polariser and the associated clamp, bolts/nuts etc in the time between now and when you want to reinstate circular in a year's time.  Also, without the polariser you may have less secure clamping arrangement.

If you do remove the polariser put it and all associated hardware in sealed bag with silica-gel drying agent.  Don't let insects enter or moisture corrosion to occur. Lock up with documentation to avoid theft or loss of knowledge as to how to re-assemble.

Best regards, Eric.
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« Last Edit: Dec 31st, 2009 at 1:03pm by Admin1 »  
 
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