An article that is geared towards helping starters of satellite TV installation. Together we shall be appraising the topic; skewing an LNBf correctly. Most of us must have been hearing about stuff like; tweak the LNBf to 3.0clock, 9.0clock, 5.0.clock or any of the sort. In this article, you will learn the basics of tweaking an LNBf to suit a particular satellite orbital position.
What is LNBf Skewing?
LNB skew can be defined as 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 Polarised Transponders.
Spectrum analysers 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 what do technicians without very expensive spectrum analyzers use?
This is where the term LNB tweaking/skewing comes in.
LNB tweaking or skewing is the setting of 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 Skewing an LNBf correctly 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”s polar mount(if you are using one) should be installed vertically upright. A spirit level(plum) 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.
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 and of course at 9 o’clock at the left-hand side.
Take note of the 9 o’clock position, this is where your LNB cable should “originate from” The image above shows an LNB set at this position. Take note of the 9 o’clock position in the photo above.
The reverse should be the case 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.
Skewing an LNBf correctly: LNB tweaking
This tutorial is for Ku band frequencies on an Offset dish but the rules can also be useful for C band as well as Prime focus dishes. However, circularly polarized signals(of C Band LNBs) do not require tweaking.
- Set your decoder to show the signal strengths of any weak transponder. Let’s start with an 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 back 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 orbital position, then the weak transponder frequencies will improve gradually until you hit the maximum signal quality receivable.
- Next, 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.