26-12-2008
|
#4 |
| Design Engineer/Installer
Join Date: 08-08-2007 Location: Central UK, E Cheshire ..near Jodrell
Posts: 987
Thanks: 74
Thanked 156 Times in 143 Posts
My System: 75e-75w C & KU, 36v h-h /36v & diseqc actuators / diseqc -USALS motors / Anlg to HD Channel Masters C120s dishes, stb's inc echo3000, lnbs, meters, custom polar mounts & elevation/incline actuator conversions... |
If it's a prime focus the LNB has to be 90 degrees and with both types... it's aim has to be to the centre of the dish. After you have modified the feed support arms so they hold the lnb level (if it's a prime focus), stand behind the lnb or the holder without the lnb in place and eye the aim of the LNB down its body through the feed horn or holder... we use a laser in place of the LNB that fits the holders.
You will need to fine tune the focal length not just rely on the calculation ...
...and you also need to match the F/D ratio for that dish... an LNBf will be completely wrong for a prime focus dish.. too shallow and cut a large area of the dish off. A C120 flanged lnb and an adjustable c120 flanged feed horn is probably your best bet to illuminate the whole dish if it's a prime focus.
The calculations for focal length & f/d ratio are not the same if it is an offset..
BTW... I would fine tune that dish on another satellite (23.5e?) or stronger beam on 28e first before attempting 2D. |
|
Last edited by pedro2000uk; 26-12-2008 at 11:22 PM.
|
|  |