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Satellite TV receivers & systems support forums
DISH SETUP: Single sat, Multi-Sat & Motorised
Dish Setup Guides, Information threads and FAQs
Multifeed installation and exact calculation of LNB position
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<blockquote data-quote="a33" data-source="post: 954871" data-attributes="member: 332642"><p>[USER=312276]@RimaNTSS[/USER]:</p><p>That is a purely toroidal dish, I believe? Nice design.</p><p>The multifeedbracket for a toroid dish is curved to the outward, that is clear. My question is primarily about a "normal" parabolical (offset) dish, though.</p><p></p><p></p><p></p><p>[USER=319227]@davemurgtroyd[/USER]:</p><p>I tend to disagree with you, here. We know and can calculate the focal point, the focal distance, the G-spot, the G-spot-distance (= effective focal distance) of a normal parabolical dish.</p><p>Exact distance calculations are given on the internet for Wavefrontier dishes (T90, T55) and Visiosat Big Bisat dishes.</p><p>On the dutch forum sat4all.com one member calculates exact LNB-distances for any parabolical dish, using G-spot-distance and the radial-calculation (see Q3 in my first post).</p><p><u>Manual adjusting afterwards usually gives deterioration of signal, not better signal.</u></p><p>Only LNB-skew needs adjusting, sometimes, due to not-exact placing of the H and V antenna in the LNB.</p><p>So: If you follow theory and your theory is sound, then you know what data you need to calculate the exact distance.</p><p>What dish-characteristics or dish-measurements do you think we need more than G-spot-distance, then, to be able to calculate the exact distances?</p><p></p><p>My big question remains: <strong>Is the focal line (or focal plane) in principle a straight line (plane) or a curved line (plane)?</strong></p><p>And if that line/plane is affected by "parabolical abberation": what corrections are needed when you go more and more off-axis? (As we all know: a spherical mirror gives spherical abberation for parallel beams, a parabolic mirror gives parabolical abberation for off-axis beams.)</p><p></p><p>I am adding two pictures to show the difference of multifeed positions: totally straight placing of LNBs, and totally curved.</p><p>[ATTACH]88662[/ATTACH]</p><p>[ATTACH]88663[/ATTACH]</p><p></p><p></p><p>Greetz,</p><p>A33</p></blockquote><p></p>
[QUOTE="a33, post: 954871, member: 332642"] [USER=312276]@RimaNTSS[/USER]: That is a purely toroidal dish, I believe? Nice design. The multifeedbracket for a toroid dish is curved to the outward, that is clear. My question is primarily about a "normal" parabolical (offset) dish, though. [USER=319227]@davemurgtroyd[/USER]: I tend to disagree with you, here. We know and can calculate the focal point, the focal distance, the G-spot, the G-spot-distance (= effective focal distance) of a normal parabolical dish. Exact distance calculations are given on the internet for Wavefrontier dishes (T90, T55) and Visiosat Big Bisat dishes. On the dutch forum sat4all.com one member calculates exact LNB-distances for any parabolical dish, using G-spot-distance and the radial-calculation (see Q3 in my first post). [U]Manual adjusting afterwards usually gives deterioration of signal, not better signal.[/U] Only LNB-skew needs adjusting, sometimes, due to not-exact placing of the H and V antenna in the LNB. So: If you follow theory and your theory is sound, then you know what data you need to calculate the exact distance. What dish-characteristics or dish-measurements do you think we need more than G-spot-distance, then, to be able to calculate the exact distances? My big question remains: [B]Is the focal line (or focal plane) in principle a straight line (plane) or a curved line (plane)?[/B] And if that line/plane is affected by "parabolical abberation": what corrections are needed when you go more and more off-axis? (As we all know: a spherical mirror gives spherical abberation for parallel beams, a parabolic mirror gives parabolical abberation for off-axis beams.) I am adding two pictures to show the difference of multifeed positions: totally straight placing of LNBs, and totally curved. [ATTACH]88662[/ATTACH] [ATTACH]88663[/ATTACH] Greetz, A33 [/QUOTE]
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Satellite TV receivers & systems support forums
DISH SETUP: Single sat, Multi-Sat & Motorised
Dish Setup Guides, Information threads and FAQs
Multifeed installation and exact calculation of LNB position
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