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<blockquote data-quote="Vipersan" data-source="post: 753284" data-attributes="member: 325666">...Ok friends ..A bit more off the wall thinking....and I've no doubt this has been discussed many times before ..Since there is a lnbf sized hole at the middle of my PF dish .....I can't help being curious about the possibility of trying the old girl in Cassegrain or gregorian mode ..So here goes ..Presumably I'd need a small parabolic sub reflector ..which when flipped would be cas or greg ..both variations capable of refocusing the signal to the hole at the centre of the Alcoa..Since the alcoa is&nbsp; a parabola ...nothing special about the shape of the sub reflector ...other than it too would be a parabola .....I guess my next question is ..would the sub reflector be approximately the same diameter as a scalar plate from a corotor...?I assume the lnbf could be fixed at the centre of the alcoa hole ...The sub reflector suspended between the legs of the tripod ..the moved in and out ..to achieve focus ...(refocus)Is that too simple ?Im assuming there would be an optimum point at which the sub reflector would illuminate the alcoa totally but that would not neccessarilly be at a point which would refocus at the same distance back to the centre hole of the alcoa....Or have I got this totally wrong ..and the sub reflector is not a parabola at all ...and is shaped otherwise ..in order to not only illuminate a specific dish ...but also to achieve focus at the middle of the dish ..where in my case the hole is ..This is just curiosity on my part ..but would appreciate input from any of you with knowledge of these things.rgdsVS</blockquote>

[QUOTE="Vipersan, post: 753284, member: 325666"] ...Ok friends .. A bit more off the wall thinking.. ..and I've no doubt this has been discussed many times before .. Since there is a lnbf sized hole at the middle of my PF dish .....I can't help being curious about the possibility of trying the old girl in Cassegrain or gregorian mode .. So here goes .. Presumably I'd need a small parabolic sub reflector ..which when flipped would be cas or greg ..both variations capable of refocusing the signal to the hole at the centre of the Alcoa.. Since the alcoa is a parabola ...nothing special about the shape of the sub reflector ...other than it too would be a parabola .. ...I guess my next question is ..would the sub reflector be approximately the same diameter as a scalar plate from a corotor...? I assume the lnbf could be fixed at the centre of the alcoa hole ... The sub reflector suspended between the legs of the tripod ..the moved in and out ..to achieve focus ...(refocus) Is that too simple ? Im assuming there would be an optimum point at which the sub reflector would illuminate the alcoa totally but that would not neccessarilly be at a point which would refocus at the same distance back to the centre hole of the alcoa.. ..Or have I got this totally wrong ..and the sub reflector is not a parabola at all ...and is shaped otherwise ..in order to not only illuminate a specific dish ...but also to achieve focus at the middle of the dish ..where in my case the hole is .. This is just curiosity on my part ..but would appreciate input from any of you with knowledge of these things. rgds VS [/QUOTE]

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