A low-noise block downconverter is thereceiving gadget mounted on satellite tv for pc dishes used for satellite tv for pc TV reception,which collects the radio waves from the dish.
Additionally known as a low-noise block,low-noise converter, and even low-noise downconverter, the gadget is sometimeswrongly known as an low-noise amplifier.
The LNB is a mixture of low-noiseamplifier, frequency mixer, native oscillator and intermediate frequencyamplifier.
It receives the microwave sign from the satellite tv for pc collected bythe dish, amplifies it, and downconverts the block of frequencies to a lowerblock of intermediate frequencies.
This downconversion permits the sign to becarried to the indoor satellite tv for pc TV receiver utilizing comparatively low cost coaxialcable; if the sign remained at its unique microwave frequency it wouldrequire an costly and impractical waveguide line.
The LNB is normally a small field suspended on a number of brief booms, or feedarms, in entrance of the dish reflector, at its focus.
The microwave sign from thedish is picked up by a feedhorn on the LNB and is fed to a bit ofwaveguide.
A number of metallic pins, or probes, protrude into the waveguide atright angles to the axis and act as antennas, feeding the sign to a PCBinside the LNB's shielded field for processing.
The decrease frequency IFoutput sign emerges from a socket on the field to which the coaxial cableconnects.
The LNB will get its energy from the receiveror set-top field, utilizing the identical coaxial cable that carries alerts from the LNBto the receiver.
This phantom energy travels to the LNB; reverse to thesignals from the LNB.
A corresponding element, known as ablock upconverter, is used on the satellite tv for pc earth station dish to convertthe band of tv channels to the microwave uplink frequency.
Amplification and noise The sign obtained by the LNB isextremely weak and it needs to be amplified earlier than downconversion.
The lownoise amplifier part of the LNB amplifies this weak sign whereas addingthe minimal attainable quantity of noise to the sign.
The low-noise high quality of an LNB is expressed because the noise determine.
This isthe sign to noise ratio on the enter divided by the sign to noise ratio atthe output.
It’s usually expressed as a decibels worth.
The best LNB,successfully an ideal amplifier, would have a noise determine of zero dB and wouldnot add any noise to the sign.
Each LNB introduces some noise however cleverdesign methods, costly excessive efficiency low-noise elements such asHEMTs and even particular person tweaking of the LNB after manufacture, can reducesome of the noise contributed by the LNB's elements.
Each LNB off the manufacturing line has a distinct noise determine as a result of ofmanufacturing tolerances.
The noise determine quoted within the specs,vital for figuring out the LNB's suitability, is normally representativeof neither that individual LNB nor the efficiency throughout the entire frequencyrange, for the reason that noise determine most frequently quoted is the everyday determine averagedover the manufacturing batch.
Block downconversionSatellite tv for pcs use comparatively excessive radio frequencies to transmit their TValerts.
As microwave satellite tv for pc alerts don’t simply move by partitions, roofs,and even glass home windows, it’s preferable for satellite tv for pc antennas to be mountedoutdoors.
Plastic glazing nevertheless is clear to microwaves andresidential satellite tv for pc dishes have efficiently been hidden indoors lookingthrough acrylic or polycarbonate home windows to protect the exterior aesthetics ofthe house.
The aim of the LNB is to make use of thesuperheterodyne precept to take a block of comparatively excessive frequencies andconvert them to related alerts carried at a a lot decrease frequency.
These lowerfrequencies journey by cables with a lot much less attenuation, so there’s muchmore sign left on the satellite tv for pc receiver finish of the cable.
It’s alsomuch simpler and cheaper to design digital circuits to function at theselower frequencies, somewhat than the very excessive frequencies of satellitetransmission.
The frequency conversion is carried out bymixing a set frequency produced by a neighborhood oscillator contained in the LNB with theincoming sign, to generate two alerts equal to the sum of their frequenciesand the distinction.
The frequency sum sign is filtered out and the frequencydifference sign is amplified and despatched down the cable to the receiver:C-band Ku-bandwhere is a frequency.
The native oscillator frequencydetermines what block of incoming frequencies is downconverted to thefrequencies anticipated by the receiver.
For instance, to downconvert the incomingsignals from Astra 1KR, which transmits in a frequency block of 10.
70 GHz,to inside a normal European receiver’s IF tuning vary of 950–2,150 MHz, a 9.
75GHz native oscillator frequency is used, producing a block of alerts within the band950–1,950 MHz.
For the block of upper transmissionfrequencies utilized by Astra 2A and 2B, a distinct native oscillator frequencyconverts the block of incoming frequencies.
Usually, a localoscillator frequency of 10.
60 GHz is used to downconvert the block to1,100–2,150 MHz, which remains to be throughout the receiver’s 950–2,150 MHz IF tuningrange.
In a C-band antenna setup, thetransmission frequencies are usually three.
Through the use of a neighborhood oscillatorfrequency of 5.
150 GHz the IF will probably be 950–1,450 MHz which is, once more, in thereceiver's IF tuning vary.
For the reception of wideband satellitetelevision carriers, usually 27 MHz huge, the accuracy of the frequency ofthe LNB native oscillator want solely be within the order of ±500 kHz, so low costdielectric oscillators could also be used.
For the reception of slender bandwidthcarriers or ones utilizing superior modulation methods, equivalent to 16-QAM,extremely steady and low part noise LNB native oscillators are required.
Theseuse an inner crystal oscillator or an exterior 10 MHz reference from theindoor unit and a phase-locked loop oscillator.
LNBFs With the launch of the primary DTHbroadcast satellite tv for pc in Europe by SES in 1988, antenna design was simplified forthe anticipated mass-market.
Specifically, the feedhorn and thepolarizer have been mixed with the LNB itself right into a single unit, known as anLNB-feed or LNB-feedhorn, and even an "Astra sort" LNB.
The prevalence ofthese mixed models has meant that right now the time period LNB is often used torefer to all antenna models that present the block-downconversion operate, withor with no feedhorn.
The Astra sort LNBF that features afeedhorn and polarizer is the commonest selection, and that is fitted to adish utilizing a bracket that clamps a collar across the waveguide neck of theLNB between the feedhorn and the electronics bundle.
The diameter of theLNB neck and collar is normally 40mm though different sizes are additionally produced.
Within the UK, the "minidish" offered to be used with Sky Digital and Freesat makes use of anLNBF with an built-in clip-in mount.
LNBs with no feedhorn built-in areusually supplied with a flange across the enter waveguide mouth which isbolted to an identical flange across the output of the feedhorn or polarizerunit.
PolarizationIt's frequent to polarize satellite tv for pc TV alerts as a result of it offers a means oftransmitting extra TV channels utilizing a given block of frequencies.
Thisapproach requires using receiving gear that may filter incomingsignals primarily based on their polarisation.
Two satellite tv for pc TV alerts can then betransmitted on the identical frequency and offered that they’re polarizeddifferently, the receiving gear can nonetheless separate them and displaywhichever one is at the moment required.
All through the World, most satellite tv for pc TVtransmissions use vertical and horizontal linear polarization however inNorth America, DBS transmissions use left and proper hand circularpolarization.
Inside the waveguide of a North American DBS LNB a slab ofdielectric materials is used to transform left and proper round polarizedsignals to vertical and horizontal linear polarized alerts so theconverted alerts will be handled the identical.
The probe contained in the LNB waveguide collects alerts which can be polarized inthe similar airplane because the probe.
To maximise the energy of the wished alerts, theprobe is aligned with the polarization of the incoming alerts.
That is mostsimply achieved by adjusting the LNB's skew; its rotation concerning the waveguideaxis.
To remotely choose between the 2 polarizations, and to compensate forinaccuracies of the skew angle, it was frequent to suit a polarizer in frontof the LNB's waveguide mouth.
This both rotates the incoming sign withan electromagnet across the waveguide or rotates an intermediate probe inside thewaveguide utilizing a servo motor however such adjustable skew polarizers are rarelyused right now.
The simplification of antenna designthat accompanied the primary Astra DTH broadcast satellites in Europe toproduce the LNBF prolonged to a less complicated strategy to the choice betweenvertical and horizontal polarized alerts too.
Astra sort LNBFsincorporate two probes within the waveguide, at proper angles to 1 one other in order that,as soon as the LNB has been skewed in its mount to match the native polarizationangle, one probe collects horizontal alerts and the opposite vertical, and anelectronic change determines which polarization is handed on by theLNB for amplification and block-downconversion.
Such LNBs can obtain all of the transmissions from a satellite tv for pc with nomoving elements and with only one cable related to the receiver, and havesince change into the commonest sort of LNB produced.
Frequent LNBs = C-band LNB=Right here is an instance of a North American C-band LNB:Native oscillator: 5.
15 GHz Frequency: three.
20 GHzNoise determine: ranges from 25 to 100 kelvins.
Polarization: Linear = Ku-band LNB=Commonplace North America Ku band LNB Right here is an instance of a normal linearLNB: Native oscillator: 10.
75 GHzFrequency: 11.
20 GHz Noise determine: 1 dB typicalPolarization: Linear Common LNBIn Europe, as SES launched extra Astra satellites to the 19.
2°E orbitalposition within the 1990s, the vary of downlink frequencies used within the FSSband grew past that catered for by the usual LNBs and receivers of the time.
Reception of alerts from Astra 1D required an extension of receivers' IFtuning vary from 950–1,950 MHz to 950–2,150 MHz and a change of LNBs'native oscillator frequency from the standard 10 GHz to 9.
The launch of Astra 1E and subsequent satellites noticed the primary use by Astra ofthe BSS band of frequencies for brand spanking new digital companies and required theintroduction of an LNB that might obtain the entire frequency vary10.
75 GHz, the "Common" LNB.
A Common LNB has a switchable localoscillator frequency of 9.
60 GHz to supply two modes of operation: lowband reception and excessive band reception.
The native oscillator frequency isswitched in response to a 22 kHz sign superimposed on the availability voltage fromthe related receiver.
Together with the availability voltage degree used to switchbetween polarizations, this permits a Common LNB to obtain bothpolarizations and the complete vary of frequencies within the satellite tv for pc Ku bandunder the management of the receiver, in 4 sub-bands:Right here is an instance of a Common LNB utilized in Europe:Noise determine: zero.
2 dB typical Polarization: LinearNorth America DBS LNB Right here is an instance of an LNB used forDBS: Native oscillator: 11.
25 GHzFrequency: 12.
70 GHz Noise determine: zero.
7 dBPolarization: Round = Ka-band LNB=Multi-output LNBs = Twin, twin, quad, and octo LNBs=An LNB with a single feedhorn however a number of outputs for connection tomultiple tuners.
Usually, two, 4 or eight outputs are offered.
Every outputresponds to the tuner’s band and polarization choice signalsindependently of the opposite outputs and "seems" to the tuner to be a separateLNB.
Such an LNB normally might derive its energy from a receiver related to anyof the outputs.
Unused outputs could also be left unconnected.
Notice: Within the US, an LNB with two outputs is termed a "twin LNB" however within the UK,the time period "twin LNB" traditionally described an LNB with two outputs, eachproducing one polarisation solely, for connection to a multiswitch and right now"twin LNB" describes antennas for reception from two satellite tv for pc positions,utilizing both two separate LNBs or a single Monoblock LNB with two feedhorns.
Within the UK, the time period "twin-output LNB", or just "twin LNB", is normally usedfor an LNB with a single feedhorn however two impartial outputs.
= Quattro LNBs= A particular sort of LNB meant for usein a shared dish set up to ship alerts to any variety of tuners.
Aquattro LNB has a single feedhorn and 4 outputs, which every provide simply oneof the Ku sub-bands to a multiswitch or an array of multiswitches, which thendelivers to every related tuner whichever sub-band is required by thattuner.
Though a quattro LNB usually lookssimilar to a quad LNB, it can’t be related to receivers straight.
Noteagain the distinction between a quad and a quattro LNB: A quad LNB can drive fourtuners straight, with every output offering alerts from the whole Kuband.
A quattro LNB is for connection to a multiswitch in a shared dishdistribution system and every output offers solely 1 / 4 of the Ku bandsignals.
= SCR/Unicable LNBs=A number of tuners may be fed from an SCR or Unicable LNB in a single cabledistribution system.
A Unicable LNB has one output connector however operates in adifferent strategy to customary LNBs so it may feed a number of tuners daisy-chained alonga single coax cable.
As an alternative of block-downconverting thewhole obtained spectrum, an SCR LNB downconverts a small part of thereceived sign chosen in accordance with a DiSEqC-compliant command from thereceiver, to output at a set frequency within the IF.
As much as 16 tuners can beallocated a distinct frequency within the IF vary and for every, the SCR LNBdownconverts the corresponding individually requested transponder.
Most SCR LNBs additionally embody both a legacy mode of operation or a separatelegacy output which offers the obtained spectrum block-downconverted tothe entire IF vary within the typical means.
Optical-fibre LNBs LNBs for fibre satellite tv for pc distributionsystems function in an identical strategy to typical electrical LNBs, exceptthat all 4 of the sub-bands in the whole Ku band spectrum of 11.
75GHz throughout two sign polarisations are concurrently block-downconverted.
Thefour sub-bands’ IFs are stacked to create one IF with a spread of zero.
45GHz, which is modulated on an optical sign utilizing a semiconductor laser, tosend down the fibre cable.
On the receiver, the optical sign isconverted again to the standard electrical sign to "seem" to thereceiver as a standard LNB.
Monoblock LNBsA monoblock LNB is a unit consisting of two LNBs and is designed to receivesatellites spaced shut collectively, usually 6°.
For instance in elements ofEurope, monoblocks designed to obtain the Sizzling Fowl and Astra 19.
2°E satellitesare well-liked as a result of they permit reception of each satellites on a singledish with out requiring an costly, sluggish and noisy motorised dish.
A similaradvantage is offered by the duo LNB for simultaneous reception of alerts fromboth the Astra 23.
5°E and Astra 19.
Chilly temperatures It’s attainable for any moisture in anLNB to bodily freeze resulting from ice build-up in very low temperatures.
Thisis solely more likely to happen when the LNB shouldn’t be receiving energy from the satellitereceiver.
To fight this, many satellite tv for pc receivers present an choice to maintain theLNB powered whereas the receiver is on standby.
In truth, most LNBs are keptpowered as a result of this helps to stabilise the temperature and, thereby, the localoscillator frequency by the dissipated warmth from the circuitry of LNB.
In thecase of UK BSkyB receivers, the LNB stays powered whereas in standby so thatthe receiver can obtain firmware updates and Digital Programme Guideupdates.
In america, the LNB related to Dish Community receiversremains powered in addition to these receivers that obtain software program andfirmware updates and information info over the air at night time.
In Turkey,one other LNB sort Digiturk MDUs are stored powered to obtain VOD content material, STBfirmware, EPG knowledge and pay TV keys with a view to watch encrypted content material.
See additionally Bias teeBlock upconverter Orthomode transducerSignal-to-noise ratio Transmit and obtain built-in assemblyDuo LNB Single Cable DistributionFibre satellite tv for pc distribution ReferencesExternal hyperlinks LNB mysteries defined.
Rationalization and block diagram of LNB Noise Temperature and Noise FigureOnAstra – Official Astra customers/viewers' siteSES – Official SES commerce/business web site Astra RecommendationsVSAT Set up Handbook with clarification of the Low-noise blockconverter.