How to install a Ku LNB on a Prime Focus Dish

[el bandido]

The ku lnb often gets overlooked when it comes to matching the lnb to a satellite dish. Hardly anybody takes the time to try and match a Ku lnb to an offset type dish, and even less attention is usually given to a Ku lnb when it is mounted on a prime focus dish.
The same techniques that are used to mount and install a C band lnb on a satellite dish may be used on a Ku lnb. There is not many of us who would want to mount a C band lnb on a dish without adjusting it for maximum performance, yet we are often satisfied to do exactly that with a Ku lnb.

The parts needed to properly install a Ku lnb on a prime focus dish are:
A Feed Tube, commonly called a Wave Guide.
A Scalar Ring to slide the Wave Guide Through.
A LNB of your choice that will connect to the Wave Guide.
A Prime Focus Mount to hold the Wave Guide on the dish.

Once you have these parts, installation of a ku lnb on a prime focus dish is identical to a c band lnb.
1. Set the depth of the Wave Guide in the Scalar ring to match the F/D of your dish.The F/D value of a dish is usually listed in the dish spec sheet.
You may calculate the F/D of your dish by taking a couple of dish measurements and applying them to a formula. The F/D of most prime focus dishes that we use be between .3 and .4. The decimal needs to be carried to two places for accuracy in adjustment.
2. Connect the LNB to the Wave Guide or Feed Tube, then mount the LNB assembly to the dish using a Ku LNB Holder.
3. Adjust LNB skew. Fine tune as needed.
4. Once the LNB feed has been adjusted correctly, tighten everything snugly and leave it alone!

I think Invacom makes pretty decent stuff for FTA so I have attached a .pdf file showing some parts from Invacom that are designed for operation of prime focus dishes in the Ku band. A picture of a ku prime focus mount is also attached.

When a mis-matched LNB is replaced with a LNB and feed that is properly matched for the dish, the difference is like going from darkness to daylight!
What we want is the entire dish area to be illuminated by the lnb without the area behind the dish being seen by the LNB. EB

[rrob311]

What do they mean by "beam width adjustment"? Is that moving wave guide in and out of the scalar ring?

[el bandido]

Yes.
Positioning the scalar ring differently on the metal waveguide will have a big effect on the lnb's illumination area. Mine is set to almost the end of the waveguide for my Fortec 1.8m Dish.