LNB skew is the rotational position of the LNB mounted on a satellite dish. It must be set within certain limits to reduce the number of errors received on both vertically and Horizontally Polarized Transponders.
Spectrum analyzers are used to set the skew by professionals installing Uplink ground stations and sometimes receiving (or downlink) satellite dishes, if they have the time. So how do technicians without very expensive spectrum analyzers use?
This is where the term LNB tweaking comes in. You probably have heard about LNB tweaking in Satellite TV forums. LNB tweaking is setting the LNB using the signal meter levels on your satellite decoder. So how is LNB tweaking done? This is a step by step process of setting the correct LNB skew on your satellite dish.
The actual “skew angle” is dependent on the satellite your dish is facing and on your location. It is also affected by how much the installed dish deviates from the vertical position. In other words your dish mount pole should be installed vertically upright. A spirit level should help you achieve this. A dish leaning on its side will not yield good results even if you use the best available LNB in the market.
The clock methodology
When installing a satellite dish, you should position the LNB using the clock methodology. This method assumes that the dish is a clock. Now when standing behind the dish, assume that the dish is an analogue clock with twelve o’clock at the top and 3 o’clock on your right.
Take note of the 9 o’clock position, this is where your LNB cable should “originate from” for lack of a better word. The featured image in this post shows an LNB set at this position. Take note of the 9 o’clock position in the photo above.
The opposite is also true, when standing in front of the dish the same position should be 3 o’clock. Whatever method you like it’s up to you.
Now set the dish to the satellite you want using a Satellite finder or whatever decoder you own. Make sure you set the dish correctly to get the maximum signal strengths.
Now this is how LNB tweaking is done
This tutorial is for Ku band frequencies on an Offset dish but the basics are the same for C band as well as Prime focus dishes. However circular polarized signals do not require tweaking.
Set your decoder to show the signal strengths of any weak transponder. Let’s start with a H, horizontally polarized transponder.
Loosen the Two screws on top of the LNB holder and rotate the LNB on its axis. Take note of how the signal quality bar behaves. There must be a point where the signal disappears completely even when the dish is correctly aligned at the correct satellite. Return the LNB to the original position.
From this position push it backwards away from the satellite dish. The following image shows the same LNB pushed forward and closer to the reflector, case A. The other image, B shows an LNB pushed all the way back away from the reflector.
Push the LNB forward and rotate the LNB within the Limits where the transponder signal quality does not go to zero. Push it forward again and rotate the LNB.
When you hit a new high signal quality level, try not to rotate the LNB, but to push it forth and back on this new position.
If the dish is correctly aligned at the satellite then the weak transponder frequencies will improve.
Switch to the other polarization, in this case V and compare the signal strengths. You should make sure that the signal strengths are consistent with each other.
When you hit the highest signal strength, tighten the screws holding the LNB.
That is how LNB tweaking is done.