Posts by PC7X

    Ok... but still it will be more important to "null" the crossed polarization than to find the maximum for the desired polarization.

    You mean, because some ASTRA satellites are transmitting with a pre-skewed setup from pretty much the same longitude, because they target west-europe?

    But even in these cases, rotating towards Es`hail-2 would do both.. right?

    This is our LNB and if I look at it in the mirror the horizontal polarization remains horizontal and the vertical polarization remains vertical. I can look at it through two mirrors but it does not change anything.

    Theoretically, that is only true if your location is either on the equator or at 25 degrees longitude.

    This picture:

    Shows it from my location without rotation of the LNB,

    you see that the red lines and the blue lines are not in the same orientation.

    That's why you want to rotate your LNB accordingly.

    If you are standing behind a normal dish with view to the satellite, the LNB has to be turned counter clock wise for all east positioned satellites. But in yor case you have an additional mirror and thus I believe your LNB has to be turned clockwise (seen from the same postion as described above).

    1) Counter clock wise because it's east from my location, or clockwise with a negative angle, still meaning counter clockwise.

    2) Then, inverted again: clock wise because of second mirror

    3) And then again: counter clock wise because the LNB IS on the back of the dish

    Conclusion: I have to turn it counter clock wise while standing behind my cassegrain dish, facing the satellite.

    And indeed Remco, if you describe your position in relation to the dish when you're about to rotate the LNB, as "Facing the satellite", then it doesn't matter if you're dish has one or two mirrors.

    My sanity check:

    1) Two mirrors would cancel each other out, when it comes to any flipping effect no matter if it's up-side-down or left-to-right

    2) So I can stand behind my dish, and just imagine how the polarisation from a satellite hanging over Africa (from the south-south-east in relation to my location) would look like:

    [Blocked Image:]


    In a linearly polarized system, a polarization misalignment of 45 degrees will degrade the signal up to 3 dB. Polarization misalignment near 90 degrees can result in signal degradation greater than 20 dB. Accurate measurements of signal strength at polarization near 0 degrees and from 80 degrees to 90 degrees require careful control of the positioner and signal strength meter.

    So it should matter something like near 1dB I estimate, and something like double that, If I rotate in the wrong direction :)

    Thanks everyone for the insight you provided.

    that is correct.. Because you want to receive H and V there is no rotation of the lnb from normal 0deg position needed.

    Not needed, well the satellite is hanging 25 degrees to the east over africa.

    When these radio waves hit my country, since we live on a sphere, I would think that indeed as calculated, for optimal reception, you would want to rotate your LNB 15.60 degrees.

    And since I only have a pretty small antenna, I would like to get the maximum out of it.

    You have no desktop or laptop with Linux installed?

    I have been using Linux on my main system since end of 1992.

    3 years later the first usable Windows system came out :)

    Arrogant linux elitist ;):P

    Just kidding of course..

    Nice to meet you here Rob.


    I calculated the needed dish setup as such:…de=nl&diam_w=60&diam_h=60

    But I am confused in which direction I should rotate my LNB for optimal reception of the linear satellite down-link.

    My satellite dish is of the cassegrain type, where I put in the LNB on the backside.

    If I would stand behind my dish, would I rotate 15.60 degrees clockwise, or counter clockwise?

    And I also assume that without LNB rotation (or elevation) the octogon F-connectors are pointing to the ground right?

    Your help is very appreciated :)