LNB's aiming point

[RimaNTSS]

Hi! I have device ready for checking where exactly LNB is pointing. Why it is important.... because, without pointing to right point you will never get maximum of your antenna. Sometimes, even on brand new antennas central LNB is not in the correct position. Of course, it is still possible to tune this antenna to maximum signal, but, unfortunately this maximum could be not real maximum. :mad:
Another question is how to find out where LNB should be pointed. On PFA aiming point is directly in the middle. On offset antenna.... OK, there are several programs for finding out this mysterious "Le point G". And, yes, it exists!

 

[Lazarus]

Ah, yes: The G Spot. I remember it well.





On pain of death!

 

[Vipersan]

Hi! I have device ready for checking where exactly LNB is pointing. Why it is important.... because, without pointing to right point you will never get maximum of your antenna. Sometimes, even on brand new antennas central LNB is not in the correct position. Of course, it is still possible to tune this antenna to maximum signal, but, unfortunately this maximum could be not real maximum. :mad:
Another question is how to find out where LNB should be pointed. On PFA aiming point is directly in the middle. On offset antenna.... OK, there are several programs for finding out this mysterious "Le point G". And, yes, it exists!

Yes indeed ..
I made such a device myself using a laser ..for centring and aiming an lnb on a PF dish..
But although it was good enough for C band ..accuracy wasn't assured for Ku band and Ka band would be worse still.
The reason for the lack of accuracy was that laser pens rarely if ever have the laser diode centred and producing a beam at exact right angles to the pen..
You can prove this for yourself easily ..
Test a couple by powering them up and placing on a flat surface ..note where the dot hits a surface at 90 degrees to the pen ..
make a mark or if using a wall ..a blob of blutack ..
Then simply roll it over the floor ..and watch the resulting dot move up and down on the wall..
I tried at least 4 ..and not one dot stayed at the same height ..
and the error of course is magnified the further from the wall you are.
To make such a device work properly ..a dedicated pen/laser which was accurately positioned and calibrated would be needed.
rgds
VS

 

[RimaNTSS]

I think easiest way how to check laser-pointer is to roll it inside of holder when pointed to dish. If beam makes sickle than true point will be right in the middle of this circle. Without doing that test, I think that diameter of this circle for my laser-pointer will be not bigger than 1cm, perhaps even smaller. will check it one day.

 

[Vipersan]

I think easiest way how to check laser-pointer is to roll it inside of holder when pointed to dish. If beam makes sickle than true point will be right in the middle of this circle. Without doing that test, I think that diameter of this circle for my laser-pointer will be not bigger than 1cm, perhaps even smaller. will check it one day.

It depends on the greatly on the FD of the dish you are setting up ...
As you indicated Rima ..
You can guesstimate it..
but wouldn't it be nice to have a laser that was centred properly in the first place ?
Not a critical requirement for those bulk sale items such as the ones on ebay sadly..

 

[RimaNTSS]

Mine pointer is not from cheap stuff, got it more than 7 years ago fro Velleman components.
But talking about mm, than for 1 meter distance (could be antenna size >180cm) if beam is making 10mm circle than it is only 0,25* mistake, and that could be quiet acceptable mistake for LNB pointing. Of course ideal laser-pointer would be better.
But there again one "but"- with laser-pointer we can check where LNB is pointing, "but" we can not make sure that LNB located right in focus of antenna! And to find focus we still need to use one of the programs available.

 

[Archived-1]

I am sure this was discussed in my 1.2 dish install from memory, I am sure I posted a link at the time, had a few beers now will look tomorrow,

 

[Trust]

With this old Inverto with a laser pointer trough the back , I can point and receive .
I drilled a tiny hole trough the antenna on the circuit board inside and it did hardly reduced the signal .
To check at wich part of the dish the lnb is looking I made a second , turnable laserpointer with adjustable angle .
I was surpriced by the effect on TRIAX dishes , after adjusting the spot on the upper edge of such dish , the spot did not reach the lower edge at all .

 

[RimaNTSS]

Thanks, Trust1! But how can you make sure your laser-pointer locatet right in the focus of antenna?

 

[Trust]

By turning it clockwise fully around in the lnb holder and making some corrections at the laser pointer holder .

 

[RimaNTSS]

Yes, but, for example here it seems that laser-pointer is not located in antenna's focus, other-ways it would be drawing circle on the ages of antenna. To m y understanding, here you should relocate place of LNB-holder and change aiming point.

 

[Trust]

Rimants , thats what I was thinking to the first time , maybe the feedarm was bended by this old mistreated dish .
So I drove to satshop Hamido (we've been there together) and tested at a new Triax and SAB dish with exactly the same result .
Both brands seem to use the lower section of the dish for the attachment of the feedarm through the dish .
Then I drove to my satfriend PaulvR here in town and tested it at a fiber Hirschmann dish with the feedarm under the dish .
There the spot was following exactly the edge of the dish .

 

[Archived-1]

This link might help.
http://www.satsig.net/pointing/finding-dish-offset-angle.htm

 

[RimaNTSS]

tested at a new Triax and SAB dish with exactly the same result .
Both brands seem to use the lower section of the dish for the attachment of the feedarm through the dish .

That automatically mean that if you place LNB to proper place (true focus) than you can gain some %% of signal, or, in another words, improve performance of dish.
This improvement could be reached by first- calculating place of focal-point and secondly by precisely pointing LNB to "Le Point G".

 

[RimaNTSS]

That was not so difficult do do test of perfectness of laser-pointer. I fixed laser-unit in front of piece of paper in distance 1,8m and found out that by turning pointer around beam draws circle about 4cm wide. That is little bit more than I was hoping. But from another hand, mistake is only 0,6*, and that could be acceptable to point LNBs.

 

[Trust]

That automatically mean that if you place LNB to proper place (true focus) than you can gain some %% of signal, or, in another words, improve performance of dish.
This improvement could be reached by first- calculating place of focal-point and secondly by precisely pointing LNB to "Le Point G".

Rimants , I thought You know me , dont You think I already tried that ? I noticed the signal result of the standard position with a BU single lnb . Lifting the feedarm and placing the rotating laser backwarts showd a perfect dish-edge-following line . Put back the BU and after adjusting the elevation of the dish tried everything , skew , lift , push forwarts , backwarts but I did not get a bether result .
With a openings angle of 60º of the BU (I dont know the real angle of that lnb) its in original position of the lnb , looking also to the lowest edge but there is a lot of overspil at the top .
Maybe its that the way the Triax should work .
On the picture , the BU fully to and backwarts
(I made a angle messuring device from the thin inox stripes in wiperblades )

 

[RimaNTSS]

Perhaps this dish is too small to see big difference of signal after slight change of the position of LNB. As for me, arm should be lowered not lifted and then correct aiming of LNB to proper point. If you have measured all the antenna's dimensions, you could calculate right focal point in Parabola program (sure you know it), and then check LNB's position.

 

[Archived-1]

Ive found the best way to get the best from any dish I have set up is find the weakest signal and make it better, works for me with a nudge L/R

 

[Trust]

Perhaps this dish is too small to see big difference of signal after slight change of the position of LNB. As for me, arm should be lowered not lifted and then correct aiming of LNB to proper point. If you have measured all the antenna's dimensions, you could calculate right focal point in Parabola program (sure you know it), and then check LNB's position.

Lowering the arm made the spotted ellips longer and smaller , then it dont cover the complete dish

 

[Channel Hopper]

Google 'Boresite and tool' (child protect on ! )