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<blockquote data-quote="2old4this" data-source="post: 1114" data-attributes="member: 174998"><p>To complete the analogy:</p><p>what happens when you pour flour through a sieve?</p><p>Some of it falls through. </p><p>Some of it does not.</p><p>The particles that are larger than the holes in the sieve do not fall through.</p><p>Well it's the same with a mesh dish.</p><p>Signals that are "bigger" than the holes will not pass through. Now it so happens that microwaves are "bigger than" the mesh gaps. IE their wavelength is longer than the diameter of the gaps in the mesh. So in principle the signals are reflected from a mesh dish just as effeciently as from a solid. </p><p></p><p>To test this, go to your kitchen.</p><p>See how your microwave oven has a metal mesh in the door with holes so you can see inside?</p><p>Now stand in front of it while it boils a mug of tea (or whatever). Are you burned? </p><p>No.</p><p>Reason: the holes in the mesh are smaller than than microwave wavelength and so the radiation is reflected back into the oven instead of leaking out to cook you.</p><p></p><p>There IS however a loss of efficiency from a mesh dish. But this has to do with a more subtle effect. All those holes effectively present a rougher surface than does a smooth solid dish. So although all signals are reflected, a small percentage of them are reflected back at the wrong angle. IE there is less concentrated signal strength arriving at the dish's focal point (where the LNB sits).</p><p>Many larger c-band mesh dishes also suffer imperfect reflections due to their segmented form. They are not perfectly parabolic.</p><p></p><p>2old</p></blockquote><p></p>
[QUOTE="2old4this, post: 1114, member: 174998"] To complete the analogy: what happens when you pour flour through a sieve? Some of it falls through. Some of it does not. The particles that are larger than the holes in the sieve do not fall through. Well it's the same with a mesh dish. Signals that are "bigger" than the holes will not pass through. Now it so happens that microwaves are "bigger than" the mesh gaps. IE their wavelength is longer than the diameter of the gaps in the mesh. So in principle the signals are reflected from a mesh dish just as effeciently as from a solid. To test this, go to your kitchen. See how your microwave oven has a metal mesh in the door with holes so you can see inside? Now stand in front of it while it boils a mug of tea (or whatever). Are you burned? No. Reason: the holes in the mesh are smaller than than microwave wavelength and so the radiation is reflected back into the oven instead of leaking out to cook you. There IS however a loss of efficiency from a mesh dish. But this has to do with a more subtle effect. All those holes effectively present a rougher surface than does a smooth solid dish. So although all signals are reflected, a small percentage of them are reflected back at the wrong angle. IE there is less concentrated signal strength arriving at the dish's focal point (where the LNB sits). Many larger c-band mesh dishes also suffer imperfect reflections due to their segmented form. They are not perfectly parabolic. 2old [/QUOTE]
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