The installation and pre-alingment of the feedhorn is very important when setting up your big dish, as this is where your signal is collected and then retransmitted through your LNB's to your satellite receiver(s). Almost all big dishes attach the feedhorn to the front on the dish by using 4 supports referred to as quad-leg supports. These supports allow for attaching and proper centering of the feedhorn to the front of the dish. The polarizer has several holes around the outer plate or scalar. These holes are aligned so you can have one combination that will allow for proper fitting to the 4 support legs. Once mounted, most poalrizers require a rotation to properly align the feed to the latitude of the installation. The directions that come with the polarizers will describe how to align the feedhorn. Below is alignment instructions provided by chaparral communications. Point the blue arrow towards your Polar Axis.
The LNBs attach to the front of the polarizer. If the system is a C/Ku band feed notice that the waveguides that the LNBs attach to are different in size. This is to allow for transmission of either 4GHz signals or 12 GHz signals. The Ku & C-Band LNB's can mount to only one waveguide (there is no "UP or "DOWN" with the LNBs).
Once everything is mounted, use a measuring tape to properly set the focal distance of the feehorn. The measurement distance can be found in the instruction manual of the dish, this measurement is from the absolute center of the dish to the to the inner ring face of the feed horn (usually plastic black or blue). If you measure from the absolute center of the dish to the front of the polarizer, this would only if you calculated the dishes focal length. Adjust the distance to nearly exactly what the dish instructions say or to what you calculated. Do not split hairs here though, a 1/4" either way will not drastically affect the performance. If you don't know your measurment then click here!