Reply to thread

Message: <blockquote data-quote="PaulR" data-source="post: 753337" data-attributes="member: 176256">My thoughts are that there a few differing reasons for using a sub-reflector.Firstly, you can have a longer focal length folded up in the length of a normal dish.  This gives a higher gain (but reduced side lobe rejection of course).Then, there's the reason of keeping the LNB close to ground so that you can cool it with liquid nitrogen.  Astronomers want the lowest noise figure for their sky searching.The Arecibo bowl gives another reason.  Obviously the bowl can't move but the sub-reflector can to give a small amount of directionability (is there such a word?).Often there will times when two, or even three, of the reasons will be invoked.  There are probably other reasons that I haven't thought of as this is just stuff off the top of my head and I might be wrong on a few things.</blockquote>