Why is the tilt on a 5-LNB Dish different?

[AlanSH]

Hi

Does anyone know why the tilt on a 5-LNB dish is different than the one on a 3-LNB dish? Looking at the satellite range (99-119) and (101-119) the tilt HAS to be roughly the same, or am I missing something? The fact that the 5-LNB centers on the 101 and the 3-LNB centers on the 110 shouldn't make a difference...

Many thanks

Alan

 

[bateau980]

I assume that the tilt is different due to the placement of the physical LNBs on the head. They're further to the left which make the angle of the dish steeper to compensate. Just don't ask me to pull out the old college algebra to try and explain. Parabolic equations is my weak point.

 

[texasbrit]

And also the 5-lnb is centred on a different satellite from the 3-lnb, so the whole design is different.

 

[bubbers44]

Hi

Does anyone know why the tilt on a 5-LNB dish is different than the one on a 3-LNB dish? Looking at the satellite range (99-119) and (101-119) the tilt HAS to be roughly the same, or am I missing something? The fact that the 5-LNB centers on the 101 and the 3-LNB centers on the 110 shouldn't make a difference...

Many thanks

Alan

Alignment of DIRECTV Ka/Ku Satellite Dish

This alignment procedure for 5LNB explains the wider arc of satellites that need to be accurately aligned because of the sharper KA peak and why 101 and 119 need to be used to make sure all will be at optimum.

 

[AlanSH]

Done some drawings to show the problem for two different zip codes:

The green line is the tilt the receiver gives for the zip code (can someone verify, please?).

The red line is the tilt I think it should be. As you can see, for the 3 LNB and the 5 LNB, the tilt is almost the same.

That the tilt given by the receiver is way off is shown on the last drawing. The skew seems to be way too much.

Hope someone can help to get to the bottom of this.

Alan

 

[charper1]

I would like to ask "to the bottom of what"; are you having reception issues? What is the reasoning for? Keep in mind as mentioned before not only the LNB placement on the PhaseIII vs the 5LNB and but also the different surface design (geometry) of the dish pan, but again; it just seems like we would all be guessing and theorizing for a problem that may not exist? Give us the scoop? I am intrigued.

 

[AlanSH]

Many people asked me to add multi-lnb support to my site DishPointer.com » Satellite Dish Pointer / Alignment Calculator with Google Maps. So I started looking into it and saw that the DirecTV dish skews provided by the receivers don't follow the conventional theory - the question is just why.

This is the full reason behind my question, hope noone minds.

 

[charper1]

Well I guess the great point is you aren't having any issues and just trying to solve a "head-scratcher"... Well cool, good luck on it.

 

[texasbrit]

And you are just looking at the difference in elevation etc for the satellites NOT the amount the dish has to be moved in order to get the signals reflected off the complex dish surface in order to hit the LNBs, which are not all at the same position of course. The numbers you have (assuming they are correct) could only show where a series of simple round dishes would have to be pointed to get the satellites.

 

[bubbers44]

I assume all dishes are exactly the same and someone at 48N and someone down in southern Fl or Central America would use the same dish with straight line alignment across the satellite field. The northern dishes would be receiving the satellites in an arc, not straight line like close to the equator because even though they are all about 22,000 miles up the elevation is a bit different through the longitude positions. It seems that to average the best signal from the middle satellites in the north a tweek slightly to improve 110 at the end of calibration might be good.
But I could be totally wrong.