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Carrier on LNB

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azizum
Ex Member


Jan 6th, 2011 at 8:04am  
Hi every one.
I am facing a problem while receiving carrier on LNB.
The carrier is being transmitted from Ku band RFT set up and I want to lock the carrier on Ku band LNB on second setup.
The LNB being used is DRO one.
Any body help me out why i am not locking carrier.
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« Last Edit: Jan 28th, 2011 at 8:40pm by Admin1 »  
 
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Eric Johnston
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Reply #1 - Jan 6th, 2011 at 11:34am  
DRO LNBs have very poor frequency stability, so if you have a narrow bandwidth carrier its actual L band frequency into the receive modem may be up to 2 MHz different from the the tuning you have configured in the modem, so it won't work.

Cheap DRO LNBs are suitable for reception of very large carriers such as 25 Msps, where a 2 MHz error can be compensated for in the receive AFC.

Typical modern DRO LNBs have stabilities of +/-500 kHz or +/- 900 kHz. See: http://mc.njr.co.jp/eng/products/vsat/ku-lnb.html

In the case of small carriers, try a PLL type LNB instead. Such PLL LNB contains a much more accurate crystal reference oscillator.

The highest stability is obtained with an external reference PLL LNB.  In this case you need an indoor 10 MHz reference oscillator, typically an ovenised crystal oscillator or an atomic standard (either actual, GPS derived or off-air).

Best regards, Eric.

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« Last Edit: Jan 28th, 2011 at 8:40pm by Admin1 »  
 
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