Reply to thread

Message

<blockquote data-quote="joddle" data-source="post: 798355" data-attributes="member: 247983">What you are dealing with as I am sure you know is a parabola - a least part of one. Once you have a parabolic shape there is a defined focus which is the point where parallel lines hitting the surface of the parabola then are bent to converge at a single point - the focus. Extending the sides of the shape without changing the shape of the centre of it mearly allows more parallel lines to converge on the same point - so actually- once you have the basic shape - extending it makes no difference to where the focal point is .However with a sat dish things get more complicated because an LBN and feedhorn are designed to &quot;see&quot; a specific angle and if you extend the dish without considering this you will simply get the same signal as before - in fact the extention will not do anything.Think of it in reverse. Imagine a torch pointing at the dish is the lnb and feedhorn and the reflector and lens of the torch concentrate the beam so it illuminates the whole area of the old dish. To get the brightest illumination you adjust the torch beam so it does not spill over the edge of the dish. This is in essence what you have before you extend you dish. Now imagine adding the petals, alas the illuminated area will be the same the new petals will remain unluinated UNLESS you readjust the lens and reflector of the torch so the light spreads more.Now in reverse, in order to get signal from the new petals you must ensure the lens (ie the feedhorn and scalar rings ) gather the signals from the extended part of the dish. This means changing the scalar rings setting or using an adjusable feedhorn. It becomes a matter of the angle seen by the lnb rather than distance from the dish.</blockquote>

[QUOTE="joddle, post: 798355, member: 247983"] What you are dealing with as I am sure you know is a parabola - a least part of one. Once you have a parabolic shape there is a defined focus which is the point where parallel lines hitting the surface of the parabola then are bent to converge at a single point - the focus. Extending the sides of the shape without changing the shape of the centre of it mearly allows more parallel lines to converge on the same point - so actually- once you have the basic shape - extending it makes no difference to where the focal point is . However with a sat dish things get more complicated because an LBN and feedhorn are designed to "see" a specific angle and if you extend the dish without considering this you will simply get the same signal as before - in fact the extention will not do anything. Think of it in reverse. Imagine a torch pointing at the dish is the lnb and feedhorn and the reflector and lens of the torch concentrate the beam so it illuminates the whole area of the old dish. To get the brightest illumination you adjust the torch beam so it does not spill over the edge of the dish. This is in essence what you have before you extend you dish. Now imagine adding the petals, alas the illuminated area will be the same the new petals will remain unluinated UNLESS you readjust the lens and reflector of the torch so the light spreads more. Now in reverse, in order to get signal from the new petals you must ensure the lens (ie the feedhorn and scalar rings ) gather the signals from the extended part of the dish. This means changing the scalar rings setting or using an adjusable feedhorn. It becomes a matter of the angle seen by the lnb rather than distance from the dish. [/QUOTE]

Verification