Editing Low-noise block downconverter (section)

{{Short description|Receiving device on satellite dishes}}
{{Antennas|components}}

[[Image:LNB dissassembled.JPG|thumb|right|A disassembled LNB. A [[Waveguide (radio frequency)|waveguide]] carrying the [[microwave]] signal ends at the hole in the center, where for this LNB two pins act as antennas (for two different [[Polarization (waves)|polarizations]]). Here the microwave signal is coupled into [[microstrip]]s on the LNB's circuit board, in order for the [[radio frequency|RF signal]] to be amplified and downconverted into lower frequencies, which are output at the two [[F connector]] sockets at the bottom.]]

A '''low-noise block downconverter''' ('''LNB''') is the receiving device mounted on [[satellite dish]]es used for [[satellite TV]] reception, which collects the radio waves from the dish and converts them to a signal which is sent through a [[Coaxial cable|cable]] to the receiver inside the building.  Also called a '''low-noise block''',<ref>{{cite web|url=http://www.satnews.com/products/glossary.html#L|title=Glossary of Satellite Terms|work=Satnews.com|access-date=January 27, 2011|archive-date=July 10, 2014|archive-url=https://web.archive.org/web/20140710053106/http://www.satnews.com/products/glossary.html#L|url-status=live}}</ref><ref>Calaz, R A. ''An Introduction To Domestic Radio TV And Satellite Reception'' CAI (2002) pp119</ref> '''low-noise converter''' ('''LNC'''), or even '''low-noise downconverter''' ('''LND'''),<ref name="WS article">Bains, Geoff. "Getting The Most Out Of An LNB" ''What Satellite & Digital TV'' (November, 2008) pp50-51</ref> the device is sometimes inaccurately called a ''[[low-noise amplifier]]'' (''LNA'').<ref>{{cite web|url=http://www.sat-universe.com/showthread.php?t=28023|title=Satellite Glossary|work=SatUniverse.com|date=23 February 2007 |access-date=January 27, 2011|archive-date=July 16, 2011|archive-url=https://web.archive.org/web/20110716005825/http://www.sat-universe.com/showthread.php?t=28023|url-status=live}}</ref>

The LNB is a combination of low-noise amplifier, [[frequency mixer]], [[local oscillator]] and [[intermediate frequency]] (IF) amplifier. It serves as the [[RF front end]] of the satellite receiver, receiving the [[microwave transmission|microwave]] signal from the satellite collected by the dish, amplifying it, and [[Downconverter|downconverting]] the block of frequencies to a lower block of [[intermediate frequency|intermediate frequencies]] (IF). This downconversion allows the signal to be carried to the indoor satellite TV receiver using relatively cheap [[coaxial cable]]; if the signal remained at its original microwave frequency it would require an expensive and impractical [[Waveguide (radio frequency)|waveguide]] line.

The LNB is usually a small box suspended on one or more short booms, or feed arms, in front of the dish reflector, at its focus (although [[parabolic antenna#Types|some dish designs]] have the LNB on or behind the reflector). The microwave signal from the dish is picked up by a [[feedhorn]] on the LNB and is fed to a section of waveguide. One or more metal pins, or probes, protrude into the waveguide at right angles to the axis and act as [[antenna (radio)|antennas]], feeding the signal to a [[printed circuit board]] inside the LNB's shielded box for processing. The lower frequency IF output signal emerges from a socket on the box to which the coaxial cable connects.

[[File:LNB 1.JPG|thumb|Cross-section across a low-noise block downconverter]]
[[File:LNB 2.JPG|thumb|Viewing of the pin and the horn antenna in a low-noise block downconverter]]

The LNB gets its power from the receiver or [[set-top box]], using the same coaxial cable that carries signals from the LNB to the receiver. This ''[[phantom power]]'' travels to the LNB; opposite to the signals from the LNB.

A corresponding component, called a [[block upconverter]] (BUC), is used at the [[satellite earth station]] ([[uplink]]) dish to convert the band of television channels to the microwave uplink frequency.