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Satellite TV receivers & systems support forums
Fringe Reception General
LNB distance to the Dish
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<blockquote data-quote="guest poster" data-source="post: 574756" data-attributes="member: 262401"><p>In practice, if you do try to calculate the focal length and F/D ratio on a standard offset dish (not a $ky dish), the calculation for the focal length can work in the vertical*, the horizontal* or diagonally*. It depends who designed the dish and unless you have that design brief to start then to find the optimum focal length is very difficult.... if say you had to make an offset LNB arm for a dish face without an arm. Probably the most reliable way is to calculate the position/ angle of the round dish face view as would be seen by an offset LNB and then calculate the optimum focal length (on that axis).</p><p></p><p>*That is that you measure D vertically and use a straight edge across the dish face vertically to gauge the depth d (or c in that example equation).</p><p></p><p>The F/D ratio should work across the horizontal for the whole (normal) offset dish. On $ky dishes the F/D ratio of the feed horn reflects the shape of the dish (plus allowing for the fact that the LNB arm is in offset).</p><p></p><p>We've modified a lot and this is sort of important to modify or check a dish if you really want the most out of it.</p></blockquote><p></p>
[QUOTE="guest poster, post: 574756, member: 262401"] In practice, if you do try to calculate the focal length and F/D ratio on a standard offset dish (not a $ky dish), the calculation for the focal length can work in the vertical*, the horizontal* or diagonally*. It depends who designed the dish and unless you have that design brief to start then to find the optimum focal length is very difficult.... if say you had to make an offset LNB arm for a dish face without an arm. Probably the most reliable way is to calculate the position/ angle of the round dish face view as would be seen by an offset LNB and then calculate the optimum focal length (on that axis). *That is that you measure D vertically and use a straight edge across the dish face vertically to gauge the depth d (or c in that example equation). The F/D ratio should work across the horizontal for the whole (normal) offset dish. On $ky dishes the F/D ratio of the feed horn reflects the shape of the dish (plus allowing for the fact that the LNB arm is in offset). We've modified a lot and this is sort of important to modify or check a dish if you really want the most out of it. [/QUOTE]
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Satellite TV receivers & systems support forums
Fringe Reception General
LNB distance to the Dish
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