LNBF Skew and Focus Adjustment....

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sanjay kumar
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LNBF Skew and Focus Adjustment....

Post by sanjay kumar »

LNBF Skew and Focus Adjustment....

After you install your LNBF on the scalar ring, you will need to make skew and focus adjustments in order to optimize signal reception.
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The skew is adjusted by rotating the LNBF either clockwise or counter clockwise. There is usually a skew scale on the LNBF. At zenith (highest point in the satellite arc) your skew should be set to 0 degrees.

The focus is adjusted by moving the LNBF in and out of the scalar ring until the signal becomes maximum. This adjustment also affects the dish illumination. Illumination refers to how much of the radio waves reflected by the parabolic dish surface actually reach the LNBF and get coupled into the waveguide. If your LNBF is too close to the dish center, your reflector will be under illuminated and won’t gather all the available radio wave energy. On the other hand, if your LNBF is too far from the dish center, your reflector will be over illuminated and the LNBF will collect background noise beyond the dish surface which will degrade your signal reception. The optimum position of the LNBF can only be found through experimentation with real signals.

Finally, it is worth mentioning that most LNBFs have 2 probes or dipole antenna elements inside the circular waveguide that project 90 degrees apart. Beneath one of the probes you will see a reflector bar. The purpose of this bar is to reflect back to the probe some additional radiation and increase the gain. The other probe uses the back surface of the waveguide as a reflector!
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inside_the_lnb.jpg
inside_the_lnb.jpg (63.22 KiB) Viewed 977 times
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