LNB “skew” angle is the rotational position of an LNB on the dish arm. The actual “skew angle” is dependent on the satellite and on your. Learn the process of Skewing an LNBf correctly. You will need the correct LNB skew in order to receive the maximum signal for your satellite. Mount it all, including the LNB, and screw it on tightly, except the screws that You will need to find out the azimut, elevation and LNB polarization/skew values.
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How to Adjust an LNB Skew
Read the Forum rules. Skew question Read times. Ex Member Ex Member. Sep 7 that 7: I’m a bit confused over a polarisation matter. I commisioned two vsats the other day.
The other looking West. Both in the Southern Hemi. I got the pol skew angle from the Service Provider. But what I thought I set right for the East looking dish didn’t make sense. I would like to send an illustration of what I mean, its a little complicated to explain. How do I upload one?
Sep 8 that 9: Reply 1 – Sep 7 that 1: What you describe is possible, assuming wkew two installations were on two different satellites. A skew angle of zero is when the dish longitude and satellite longitude are identical. This is also the point where azimuth is And for me it’s easier to understand skew if I’m behind the dish. If your azimuth is less than 90 degrees, you’re pointing left. Skew would be CCW as viewed from behind. If your siew is more than 90 degrees, you’re pointing right.
Skew would be CW. This is true regardless of hemisphere.
What is LNB Skew?
So the discrepancy might also be as simple as human error. Reply 2 – Sep 8 that 9: To put picture in your message at this forum you may: Upload the image to your own server or to a public image server. Alternatively send your image to me by email eric satsig. Regarding applying the polarisation adjustment amount, if you are in the southern hemisphere: For satellites to the north west the polarisation adjustment amount is anticlockwise, as viewed facing towards the satellite in the sky.
For satellites to the north east the polarisation adjustment amount is clockwise, as viewed facing towards the satellite in the sky.
For the satellite due north the polarisation adjustment amount is zero. This is vertical polarisation LNB waveguide: If applying the adjustment amount causes the LNB to hit metal then start on the other side.
I prefer to always consider the view towards the satellite in the sky. It is then quite obvious that, in the southern hemisphere, for satellite to the north west you turn the feed anticlockwise and clockwise for a satellite in the north east. Start with the correct polarisation name. Then apply the adjustment amount. Note that ln scale readings may start at 0, 90, and go forwards or backwards.
Ignore the numbers and simply count the required amount along the scale. What are your pointing angles as per http: Sep 16 thsjew 7: Profile, Options, Top line Posts: Reply 3 – Sep 11 that Note in the above table: The red arrow V is the BUC transmit polarisation. The blue arrow H is the LNB receive polarisation. One of each pair ske green lines should be deleted from the diagram.
The earth station cannot be transmitting on both polarisations simultaneously. The view is taken facing into the dish with your back to the satellite in the sky. The third line of text is best ignored to avoid confusion. To start discussing the satellites polarisation is confusing.
Akew the satellite transmits vertical parallel with the earth’s axis it is called vertical name when it arrives at the earth station. In the last line of text where is says horizontal, this refers to the BUC transmit polarisation. In this picture above the receive polarisation is shown by the orange line.
The LNB was intially at the side true nominal vertical receive polarisation and has been adjusted downwards by 22 deg wrong amountsee red lines. The required adjustment amount is 57 deg so the LNB could be pushed downwards further or, skea start again on the other lng, and push the LNB upwards by an amount of 57 deg as shown in pink.
Sep 15 that 9: Reply 4 – Skea 22 ndat I just want to return to this topic for a sec. I’m South of the equator so I’m pointing East. The diagram shows what I mean. What do you think? Andrew feed with xpol omt.
Lnbs on both feed ports sekw only. JPG 18 KB Reply 5 – Aug 22 ndat 1: Either figure can be correct, depending on where is the start position and which way you look at soew feed. My satsig definition is “The amount of adjustment angle required, as viewed while standing behind the dish and facing forwards towards the satellite in the sky, positive is clockwise”.
If you are in the southern hemisphere and facing north east then you need to turn the feed by an amount clockwise, as viewed while standing behind the dish and facing forwards towards the satellite in the sky. Remember to start with true vertical receive polarisation, if that is what you want, as you would if wanting vertical polarisation on a satellite high up at due north. Either side is vertical receive polarisation. Choose one side if the other results in the LNB hitting metal when the adjustment is applied.
Vertical receive polarisation LNB input waveguide If you have a spectrum analyser, adjust for minimum xpol interference level. The wanted signal will have a broad ill-defined maximum, the cross pol signal will have s,ew sharp narrow null.
Go for the middle of the null, about 2 skwe wide. If co-pol and x-pol are the same level you have 45 deg error. Reply 6 – Sep 14 that 7: It’s been a while since I’ve been on but good to be back. I’ve been scratching my head over this one until now, apparently the beam of this particular craft is offset skewed skeq 45 deg so at the remote the pol adjustment has to skew a further 45 deg to match.
Its also been ksew out that the prodelin waveguide has a lbn machined into the inside of the throat to account for this, although I didn’t get a chance to open it to see. It’s a real doozy for those in the field presetting the typical pol with no luck tuning off a moderate eirp.
Reply 7 – Sep 15 that 9: Linear polarised satellites normally have their polarisations parallel to or at right angles to the earth’s axis and equator. If you are told a polarisation you need to know if this refers to the uplink or downlink.
They are normally opposite and very rarely the same skwe. Start with the named nominal polarisation. Vertical means that the broad faces of the rectangular waveguide will be on top and underneath. There will be a polarisation adjustment amount required.
I give only the adjustment amount and its direction. You need to apply the adjustment amount using whatever scale or tick marks provided.