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Satellite TV receivers & systems support forums
DISH SETUP: Single sat, Multi-Sat & Motorised
hook 2 stb's to 1 lnb
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<blockquote data-quote="spiney" data-source="post: 179473" data-attributes="member: 192438"><p>Well, my guide does say, fairly clearly, but ......</p><p></p><p>Each dbs satellite transmits in a 2 Ghz bandwidth, on both vertical and horizontal polarisations, which makes a total bandwidth of 4 Ghz.</p><p></p><p>To get all that direct to a sat receiver, you'd have to actually use metal waveguide, completely impracticable in a consumer product (would cost several thousand pounds, maybe tens).</p><p></p><p>So system used is to "downconvert" the received 12 Ghz ku band to 1-2 Ghz so-called "satellite intermediate frequency", in the lnb, which allows much cheaper coaxial cable to be used.</p><p></p><p>Even reduced bandwidth 2 Ghz won't "fit" onto a coax. Therefore, the received 4 Ghz bandwidth is divided into 4 different so-called "polarities", each 1 Ghz wide, which "comfortably" travels down coax in TEM mode, though it's still high loss and special sat cable is needed.</p><p></p><p>The sat receiver then "choses" which polarity it wants, out of 4, by sending control signals back up cable to lnb.</p><p></p><p>If 2 sat receivers, or more, share a single lnb output, then there's only a 1 in 4 chance they'll want the same polarity - with just a quarter of total channels - otherwise their control signals will clash. Depending, it's possible to have neither of 2 receivers getting the wanted channel, and adding more receivers just makes things worse.</p></blockquote><p></p>
[QUOTE="spiney, post: 179473, member: 192438"] Well, my guide does say, fairly clearly, but ...... Each dbs satellite transmits in a 2 Ghz bandwidth, on both vertical and horizontal polarisations, which makes a total bandwidth of 4 Ghz. To get all that direct to a sat receiver, you'd have to actually use metal waveguide, completely impracticable in a consumer product (would cost several thousand pounds, maybe tens). So system used is to "downconvert" the received 12 Ghz ku band to 1-2 Ghz so-called "satellite intermediate frequency", in the lnb, which allows much cheaper coaxial cable to be used. Even reduced bandwidth 2 Ghz won't "fit" onto a coax. Therefore, the received 4 Ghz bandwidth is divided into 4 different so-called "polarities", each 1 Ghz wide, which "comfortably" travels down coax in TEM mode, though it's still high loss and special sat cable is needed. The sat receiver then "choses" which polarity it wants, out of 4, by sending control signals back up cable to lnb. If 2 sat receivers, or more, share a single lnb output, then there's only a 1 in 4 chance they'll want the same polarity - with just a quarter of total channels - otherwise their control signals will clash. Depending, it's possible to have neither of 2 receivers getting the wanted channel, and adding more receivers just makes things worse. [/QUOTE]
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Satellite TV receivers & systems support forums
DISH SETUP: Single sat, Multi-Sat & Motorised
hook 2 stb's to 1 lnb
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