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Satellite TV receivers & systems support forums
DISH SETUP: Single sat, Multi-Sat & Motorised
23mm LNB vs 40mm
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<blockquote data-quote="s-band" data-source="post: 1022783" data-attributes="member: 407744"><p>C120 flange has a 19mm internal diameter and using</p><p><a href="http://www.rfwireless-world.com/calculators/circular-waveguide-cutoff-frequency-calculator.html" target="_blank">Circular Waveguide frequency calculator | converters and calculators</a></p><p>gives a cut-off of 9.3GHz that's the low frequency limit and it's best to keep clear of it.</p><p></p><p>On the high side things go wrong if the guide is over-moded which is a bit more complex. Practical effects can be confusing.</p><p><a href="http://www.rfcafe.com/references/electrical/circular-waveguide-modes.htm" target="_blank">Properties of Circular Waveguide Modes (formulas) - RF Cafe</a></p><p><a href="http://www.rfcafe.com/references/electrical/waveguide.htm" target="_blank">Rectangular & Circular Waveguide: Equations & Fields Formulas & Calculator - RF Cafe</a></p><p></p><p>Useful table for standard circular guide sizes: <a href="http://www.cernex.com/PRODUCTS_NEW/Tech_info/Circular%20Waveguide%20Sizes.pdf" target="_blank">http://www.cernex.com/PRODUCTS_NEW/Tech_info/Circular Waveguide Sizes.pdf</a></p><p></p><p>I have no evidence but I would have thought that the small diameter ones that are not so good are those that use dielectric feeds or under-size horns. If you take the plastic off most modern LNBFs you'll fine the innards are 22mm ish outside diameter. (Octagon PLL single is 21mm o/d)</p><p></p><p>Edit: RimaNTSS beat me to it</p><p>Edit 2: Attached a pic of one I pulled apart some time ago</p><p>[ATTACH]109232[/ATTACH]</p></blockquote><p></p>
[QUOTE="s-band, post: 1022783, member: 407744"] C120 flange has a 19mm internal diameter and using [URL='http://www.rfwireless-world.com/calculators/circular-waveguide-cutoff-frequency-calculator.html']Circular Waveguide frequency calculator | converters and calculators[/URL] gives a cut-off of 9.3GHz that's the low frequency limit and it's best to keep clear of it. On the high side things go wrong if the guide is over-moded which is a bit more complex. Practical effects can be confusing. [URL='http://www.rfcafe.com/references/electrical/circular-waveguide-modes.htm']Properties of Circular Waveguide Modes (formulas) - RF Cafe[/URL] [URL='http://www.rfcafe.com/references/electrical/waveguide.htm']Rectangular & Circular Waveguide: Equations & Fields Formulas & Calculator - RF Cafe[/URL] Useful table for standard circular guide sizes: [URL='http://www.cernex.com/PRODUCTS_NEW/Tech_info/Circular%20Waveguide%20Sizes.pdf']http://www.cernex.com/PRODUCTS_NEW/Tech_info/Circular Waveguide Sizes.pdf[/URL] I have no evidence but I would have thought that the small diameter ones that are not so good are those that use dielectric feeds or under-size horns. If you take the plastic off most modern LNBFs you'll fine the innards are 22mm ish outside diameter. (Octagon PLL single is 21mm o/d) Edit: RimaNTSS beat me to it Edit 2: Attached a pic of one I pulled apart some time ago [ATTACH]109232[/ATTACH] [/QUOTE]
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DISH SETUP: Single sat, Multi-Sat & Motorised
23mm LNB vs 40mm
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