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Fringe Reception General
Made a start on my petal extensions ..
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<blockquote data-quote="Vipersan" data-source="post: 801430" data-attributes="member: 325666"><p>Having now altered the tilt by approx 1cm on 4 wings I was able to measure and get a rough idea of what the new focal distance would be ..</p><p></p><p>The original dish was re-measured and the various aspects are as follows:-</p><p></p><p>1.8 mtr (180cm) </p><p>Dish depth 25.3 cm</p><p>Therefore FD ratio 0.44</p><p>Focal distance to lnb 80.04</p><p></p><p>With the wings added and tilt altered a bit</p><p>it makes the dish a small ammount deeper</p><p></p><p>diameter 219cm</p><p>Depth 36.5cm</p><p>FD ratio 0.38</p><p>Focal distance to lnb 82.13</p><p></p><p>So by my reconing I'm still 2cm out</p><p>How critical this 2cm will be is as yet an unknown quantity ..</p><p>So I have a choice to either increase the tilt some more ..with packing wedges</p><p>Or work on the assumption that I will not 'effectively' be using the last few cm of the dish for signal gathering.</p><p>Comments on this would be helpful and welcome</p><p></p><p>What it does clearly tell me is that I will have to shift the lnb relative to the scalar feed plate ..and this will always be a compromise.</p><p>Don't you just hate it when you get your sums wrong ..even by such a small ammount.</p><p>My teacher would have given me a big red X and 'see me' at the bottom of the sheet.</p><p>rgds</p><p>VS</p><p></p><p>I've probably asked this before ..but I'll risk repeating myself ..</p><p>Should the front or back of the scalar feed be placed at the focal distance ...and the lnb set to the correct fd ratio using the integrated scale _within_ the scalar feed ..</p><p>OR</p><p>Should the front edge of the LNB be placed the focal length ..and the the scalar feed then be adjusted to the correct FD ratio as shown on the scale.</p><p>Something I have taken forgranted in the past ..and just set the lnb and scalar plate roughly at the focus and tweaked for maximum signal on a weak channel ..</p><p>Not very scientific ...but since the FD ratio will now change quite dramatically ..I'd like to get to grips with this properly.</p></blockquote><p></p>
[QUOTE="Vipersan, post: 801430, member: 325666"] Having now altered the tilt by approx 1cm on 4 wings I was able to measure and get a rough idea of what the new focal distance would be .. The original dish was re-measured and the various aspects are as follows:- 1.8 mtr (180cm) Dish depth 25.3 cm Therefore FD ratio 0.44 Focal distance to lnb 80.04 With the wings added and tilt altered a bit it makes the dish a small ammount deeper diameter 219cm Depth 36.5cm FD ratio 0.38 Focal distance to lnb 82.13 So by my reconing I'm still 2cm out How critical this 2cm will be is as yet an unknown quantity .. So I have a choice to either increase the tilt some more ..with packing wedges Or work on the assumption that I will not 'effectively' be using the last few cm of the dish for signal gathering. Comments on this would be helpful and welcome What it does clearly tell me is that I will have to shift the lnb relative to the scalar feed plate ..and this will always be a compromise. Don't you just hate it when you get your sums wrong ..even by such a small ammount. My teacher would have given me a big red X and 'see me' at the bottom of the sheet. rgds VS I've probably asked this before ..but I'll risk repeating myself .. Should the front or back of the scalar feed be placed at the focal distance ...and the lnb set to the correct fd ratio using the integrated scale _within_ the scalar feed .. OR Should the front edge of the LNB be placed the focal length ..and the the scalar feed then be adjusted to the correct FD ratio as shown on the scale. Something I have taken forgranted in the past ..and just set the lnb and scalar plate roughly at the focus and tweaked for maximum signal on a weak channel .. Not very scientific ...but since the FD ratio will now change quite dramatically ..I'd like to get to grips with this properly. [/QUOTE]
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Fringe Reception General
Made a start on my petal extensions ..
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