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Thread: Offset LNB

  1. #1
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    Default Offset LNB


    Who knows the beamwidth or viewing angle from offset lnb's?
    I always find 90°.
    For prime focus lnb's we can change it with scalar ring (F/D ratio),but for offset lnb's it is not possible.

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    Default Re: Offset LNB

    Quote Originally Posted by Kaefi
    Who knows the beamwidth or viewing angle from offset lnb's?
    I always find 90°.
    For prime focus lnb's we can change it with scalar ring (F/D ratio),but for offset lnb's it is not possible.
    What is your problem with your LNBF?

  3. #3
    bombastik
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    beamwidth and look angle are specs of antenna dish not lnb as far as i know, the larger the dish the narower the beamwidth more gain, look angle depends on the geometry of the dish, with offset type usually 27 degrees compare to prime focus type.

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    Default

    I did not ask about the beamwidth of an antenna,which can be easily calculated.
    I asked about the feedhorn beamwidth or the viewing angle from offset lnb's or the F/D ratio.
    For a prime focus lnb you can change the viewing angle or F/D ratio with the scalar ring.
    But with offset lnb's it is not possible,it is fixed.
    My suggestion: F/D = 0,5 and viewing angle 90°

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    Quote Originally Posted by Kaefi
    I did not ask about the beamwidth of an antenna,which can be easily calculated.
    I asked about the feedhorn beamwidth or the viewing angle from offset lnb's or the F/D ratio.
    For a prime focus lnb you can change the viewing angle or F/D ratio with the scalar ring.
    But with offset lnb's it is not possible,it is fixed.
    My suggestion: F/D = 0,5 and viewing angle 90°
    Why worry on something you can not change!

  6. #6
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    Firstly are you talking about C-band off-set or Ku off-set.

    C-band off-set will require a scalar ring as a normal prime focus dish does , except the rings on the scalar ring are cut at an angle to fit in with the dish, and focal length can be adjusted in the normal way.

    With Ku, the angle of the LNB in relation to the face angle of the dish is dependant on the dish size, as each dish size has a differant angle. The easest way to get the angle and settings for a off-set LNB arm, is to hold the LNB in front of the dish and move it rounfd slowly until you find a signal, then measure the distance from the dish, and make up a set of arms to suit.
    regards from OZ bassett

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    I have a prime focus dish with a diameter of 610cm, focal length 239cm and the feedhorn beamwidth is 130,6 degrees.

    Now there is the question if my invacom offset lnb (0,3 db) will "see" the whole dish or only a part of it.

    Anyhow I have also a prime focus lnb from invacom (0,3db) with feedhorn and adjustable scalarring - but with the offset lnb I get a stronger signal.

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    As far as I know , the dish could be offset and not LNB.

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    Quote Originally Posted by Kaefi
    I have a prime focus dish with a diameter of 610cm, focal length 239cm and the feedhorn beamwidth is 130,6 degrees.

    Now there is the question if my invacom offset lnb (0,3 db) will "see" the whole dish or only a part of it.

    Anyhow I have also a prime focus lnb from invacom (0,3db) with feedhorn and adjustable scalarring - but with the offset lnb I get a stronger signal.
    Offset LNBF has a wider F/D ratio (.5 to .7) specification which makes it receive more signal that prime focus lnb. But if the prime focus LNB is located on the proper location, it will receive same amount of signal as the Offset LNBF.

 

 

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