Low Noise Block-downconverter (so called because it converts a whole band or "block" of frequencies to a lower band).
Also incorrectly known as a "Low Noise Block" or a "Low Noise Blocker"!
An LNB sits on the end of an arm and faces the parabolic reflector ("dish") which focusses the signals from a satellite 24,000 miles away into the "feed horn" of the LNB (see pictures below).
The LNB converts the signals to a lower frequency and sends them out to the cable connector, which you connect to your satellite receiver via coaxial cable.
What is an LNBF? This is the term for an LNB with an integral feed horn. Nowadays the "F" tends to be omitted.
What is an LNC? Low Noise Converter. Basically the same thing.
A modern "universal" LNB is able to operate in four modes to provide signals from four frequency bands, known as "low-horizontal", "high-horizontal", "low-vertical" and "high-vertical". An LNB may have more than one output but any one output can provide only ONE of these bands at a time.
In order to tell the LNB output which of the four frequency bands it needs to provide, the receiver "communicates" with the LNB as follows (this gets technical):-
A modern "Universal" LNB requires a 22 kHz signal at 0.5v p-p to switch its Local Oscillator to 10.6 GHz ("high band"). Otherwise it uses its 9.75 GHz oscillator.
Polarisation switching is controlled by DC voltage supplied by the receiver. 12.5v to 14.5v gives vertical and 15.5 to 18v gives horizontal polarisation. A higher voltage than that can damage the LNB. A voltage that is too low will prevent the LNB from working correctly.
Under normal circumstances, one cable can carry only one LNB feed (because of the voltage and tone communication method), although it is sometimes possible to use a "stacker-destacker" to carry two.
Sky "universal" LNBs designed to work with a UK "Sky minidish" are very specifically optimised for the "wide oval" shape. However, that dish/LNB combination can also be used for broadcasts other than those provided by BskyB (e.g. Freesat and strong foreign signals).
Note that there are two sizes of "Sky Minidish: the "zone 1" dish is about 54cm wide; the "zone 2" dish is about 70cm wide and is used in areas of the UK where the signal is weaker (e.g. Scotland).
There are two other types of "universal" LNB, which can also be used with the "circular" dish shape for which they were designed:
40mm neck type. Normally used with an "offset focus" dish, which is very slightly "tall oval" but actually looks circular from the LNB's position.
C120 flange type. This doesn't have an integral horn but a flange, designed to be bolted to the feedhorn of a "prime focus" circular dish.
It is possible to "bodge" an LNB onto the "wrong" type of dish and it will receive signals. However, it will also receive more unwanted interference, which could compromise reception where the wanted signal is weak (especially during precipitation).
We try to stock the "best" available. For example, the "Invacom quad" has the best cross-modulation performance of all the LNBs I've had tested. In layman's terms, this means that a weak transmission on one polarisation is less likely to be drowned out by an adjacent strong signal on the opposite polarisation. This parameter will be of interest ONLY for a dish of 2m diameter or larger. On an 80 cm dish you might as well use the cheapest LNB you can find because it won't be able to collect a strong enough signal to cause this cross-modulation problem.
As another example, the (obsolete) Thomson Sky LNB was said to have a higher gain than usual. (This is hearsay - I never had it measured). The result was (allegedly) that it could be used with a longer length of cable BUT, some receiver tuners got overloaded if it was used with a short length of cable. So you might say that this LNB would "perform better" with a long cable run (but it might be crap with a short length).
An important point to recognise is that an LNB will work at its best when it matches the dish. This means that an LNB which is designed to focus on a dish which is circular (when viewed from the LNB position) will not give its best if you fit it to a dish that is wider than its height - and vice-versa.
In addition, the LNB must be fitted so that it sits at the exact focal point. A couple of millimetres either way will reduce the amount of signal and increase the amount of interference. The LNB "skew" (rotational position) must also be correct, otherwise signals of opposing polarisation will interfere with each other.
Assuming that you've chosen the correct type of LNB and got the adjustments right, it's unlikely that you'll benefit from changing it for a different make of LNB. You'll see all sorts of silly claims such as "0.2 dB noise figure". Believe me when I tell you that any noise figure below 0.9 dB is fine. You won't see any difference whatsoever - even if the claimed noise figure is correct. Dish size is what matters, and dish quality. There are some dishes on sale which are flimsy and poorly made. We don't stock these. If you buy on price alone, be prepared for disappointment and bear in mind that it's much easier to swap an LNB than a dish.
If you swap an LNB and see an improvement, it's likely that the first LNB was OK but was designed for another dish and probably didn't have the range of adjustment required to set it at the exact focal point. OR the connections had been made without applying silicone grease and the copper wire had corroded. More about this .. click HERE.
However, LNBs can and do fail so don't discount the LNB when you look for fault causes.
Note: we stock LNBs for Sky dishes and LNBs for "circular" dishes. Do not mix the two. As far as we can tell, the LNBs that we supply match their respective dishes adequately, so there's no point asking us about this before purchase. However, if you find a problem after purchase, we do want to hear about it.
What is Noise Figure?
LNB Noise Figure Graph
The graph shows a typical result of measuring the unwanted noise generated by two LNBs across their frequency range (horizontal axis). Low is good.
The red line shows a "0.2dB minimum" LNB and the blue line shows a "0.4dB minimum" plot.
Bearing in mind that the ideal situation is to have a minimum amount of noise across the entire frequency band, which LNB would you prefer?
Every LNB is different because of manufacturing tolerances. Measuring LNB noise is time-consuming and can't be done for LNBs selling for just a few pounds each. Instead, the manufacturer will make a few checks at specific frequencies (not across the whole band) on a few random samples.
Without a full graph showing the actual measurements of the LNB that you buy, it's impossible to know what you've got. The manufacturer may state a "typical" or "minimum" noise figure but that's based on measurements of only a few random samples at a specific frequency.
In the end, you have to rely on results. If a lot of people say (for example) "the zzzzzz quad-output LNB works for me in a fringe reception area with a dish made by xxxx and a receiver made by yyyy" then that's probably the best information you are going to get.
(If you are not in a "fringe reception area", just buy the cheapest. It won't make ANY difference whatsoever to your picture quality or rain margin. The dish size is MUCH more important. If in doubt, buy a "Sky zone 2 minidish" or larger.)
The "0.1dB" specification is utterly meaningless. Seriously, once the noise figure is below 0.6dB right across both bands (Hi and Lo), then lowering it further (even if that were technically possible, which it isn't) would make no discernible difference to reception.
Q. Can you supply a 0.1dB LNB please?
A. Unfortunately, there's no such thing. Please don't be fooled by marketing hype.
Even if we paid £100 for an LNB, the manufacturer couldn't guarantee 0.1dB max. noise across both Hi and Lo bands in real world conditions.
Of course, that doesn't stop crafty sellers from sticking a label on and relying on the fact that nobody has the £50,000 equipment to prove them wrong.
You should also bear in mind that there are other important parameters:-
This is the amplification factor and, again, it varies across the frequency range, just like the noise factor does. The Gain determines how strong the signal is when it is sent down the cable. Ideally you want a high gain and a low noise factor for a long cable but the two are mutually exclusive so you won't get it. For a short cable run you don't want a high gain because there's a risk of overloading the tuner inside the receiver - especially with a large dish.
CROSS POLAR REJECTION
Satellite signals from the Astra satellites (and most others viewable in the UK) are transmitted in either vertical or horizontal polarisation. A "universal" LNB can switch between the two and this switching is controlled by the LNB voltage supply: 13v gets you vertical and 18v gets you horizontal polarisation. But signals of different polarisation can interfere with each other. The ability of an LNB to prevent this is called its "cross-polar rejection" (CPR) and is measured in deciBells.
CPR is important if you are in an area of fringe reception where one polarisation is much stronger than the other. If the LNB can't reject the unwanted signal, it will swamp the weaker one resulting in "No satellite signal". In general, CPR isn't going to matter with a dish less than 1.8m in diameter.
A universal LNB can receive signals from two separate frequency bands - high and low. The associated satellite receiver "tells" the LNB to use High Band by sending a 22kHz tone up the cable. Without the tone, the LNB will revert to Low Band.
The satellite transmits signals which are horizontally polarised and vertically polarised, which minimises interference between adjacent frequencies. The receiver "tells" the LNB which polarisation to "look at" by supplying it with 13 volts (V) or 18 volts (H). In addition, the LNB rotational position ("skew") has to be set to the correct angle so that horizontal and vertical signals are received with equal strength. The best guide to the correct "skew" position on a Sky Digibox is the "signal quality" indicator. Rotate the LNB for the highest reading.
SPLITTING THE FEED
Because the LNB is looking for a steady 13 volt or 18 volt supply and a steady 22kHz tone, you can't "split the feed" to drive two receivers unless you appreciate that one receiver will always "win". The receiver supplying 18 volts and 22kHz tone will win over the other. That's fine if both programmes happen to be on (for example) High Band, Horizontal Polarisation but otherwise you'll get a conflict. The answer is to use an LNB with multiple outputs - usually a "quad-output" LNB.
How to test an LNB?
I think my LNB is faulty. How can I test it?
The only way to fully test an LNB is to fit it to a suitably aligned dish and connect a satellite receiver. Then check to make sure every channel is there. If no channels are missing and if it continues to work through a hot day and a cold night, the LNB is fine.
However, if some channels still appear to be missing (with a known good LNB), this could be the fault of the cable (bad connection, water ingress or kinked or wrong type), the receiver or the dish (distorted or misaligned) or local interference (DECT phone, car radar detector, etc.). So then you need to use a process of elimination by swapping the dish, the cable and the receiver (for a different make/model as some receivers won't work correctly with some LNBs). Note that some wall-plate connectors can also cause "channels missing" problems and some electronic devices (DECT 'phone base stations, "Snooper" type radar detectors and microwave ovens) can cause similar problems. I've even had it reported that a bad battery connection in a laptop computer wiped out some channels!
Can't I test it with a meter?
You can NOT test an LNB with a multimeter.
A cheap Satfinder meter is more useful but it simply looks at the average strength of all frequencies. It will not tell you if some frequencies are missing. An expensive meter looks at a specific frequency (sometimes more than one) but it will not tell you if some frequencies are missing.
Also, most meters rely on battery power. If the battery can not supply enough current to the LNB, it may give a false reading.
In short, you can not fully test an LNB with any meter but you can perform a partial test.
Could I have damaged my LNB?
A "universal" LNB is designed to operate normally with an input voltage of up to 20 volts. At a somewhat higher voltage, you can expect the LNB to fail. The time taken to fail depends on the applied voltage and duration. It would take a highly unusual fault to cause a Digibox to provide more than 20 volts and any digibox that did so would almost certainly emit expensive smoke within seconds.
Is my LNB causing Grainy Pictures?
Because the signals for digital channels are "multiplexed" together, the satellite TV receiver has to decode them and piece them back together. This means that neither the LNB nor the cable connecting it to the receiver can cause "noisy" or "grainy" pictures. Digital is an "all or nothing" system. You either see a perfect picture (as perfect as the original transmission) or else an extremely broken picture or no picture at all. There is no inbetween stage as there was with analogue. So, if you are seeing "grainy" pictures, the fault must lie in the receiver (rare) or the TV (rare) or in the cable connecting them together. It could be caused by interference in your house or it could simply be your imagination.
What LNB do I need for HD/SD?
All modern receivers use a "universal" LNB which is compatible with all signals. Make sure that the LNB you choose has sufficient outputs for your receiver(s) which will have one or two inputs each. You can not "split" the LNB cable because each receiver input controls its own LNB output exclusively.
What LNB do I need for DiSEqC?
DiSEqC is a signalling protocol used by some receivers (not Sky) to control an LNB switch or a dish positioner. It is also used by some LNBs which have a built-in DiSEqC switch. This type of LNB is called a "Monobloc" or "Dual-horn" LNB.
Can I split the feed from one LNB to two tuners?
Yes but it won't work properly. You should fit an LNB with more outputs.
In theory, all LNB outputs are equal so it doesn't matter which you use. Protect unused outputs with a lump of "Blu-Tack" or other weatherproof seal.
In practice, we've had reports that the centre two outputs of an Invacom quad-output LNB produce a slightly better signal than the outer two when fitted to a large dish of 1.8m diameter or greater. We have not tested this theory and it applies only as stated; it does not apply to any other LNB or to a smaller dish size.
If you use a Quattro LNB then the order of connection to a multiswitch does matter!
List of Universal LNB types:
The term "universal" is used to describe an LNB that has "dual band" tuning capability. It came after the "enhanced" LNB which had a slightly extended tuning range and used a 9.75 GHz oscillator instead of 10.0 GHz. Some people mistakenly think that "universal" refers to "universal fitting", meaning the LNB will fit any dish. There is no such LNB. It's important to choose an LNB which is suitable for your dish and matches your receiver. (All modern "digital" receivers in the UK will work with a "universal" LNB. The same is NOT true for the USA.)
A Universal LNB requires a 22 kHz signal at 0.5v p-p to switch its Local Oscillator to 10.6 GHz ("high band"). Otherwise it uses its 9.75 GHz oscillator ("low band"). Used by ALL modern satellite receivers for Sky, Freesat, FTV and FTA viewing.
Polarisation switching is controlled by dc voltage supplied by the receiver. 12.5v to 14.5v gives vertical and 15.0 to 18v gives horizontal polarisation. A higher voltage than that may damage the LNB but most are OK up to 20v. A voltage that is too low (less than 12.5v) will prevent the LNB from working correctly.
Single-Output universal LNBs
Note: single-output LNBs are seldom used nowadays unless you have a specific reason - such as squeezing several LNBs together on one dish. Most people keep their options open by fitting at least a quad-output LNB, which provides four separate feeds for (say) four satellite TV receivers or two Sky+ or HD PVRs. (You can't split an LNB feed so be sure to install an LNB with as many outputs as you are likely to need in the future.)
Typical single-output "Universal" LNB 9.75 and 10.60 GHz L.O.
The (obsolete) Cambridge "Platinum" Geo Universal G57" LNB
Works in 2 bands* 10.7-11.8 and 11.6 - 12.7 GHz. (22 kHz signal switched). Noise Figure usually 1.0 dB or better. Integral feed horn with 40 mm neck but C120 flange type available in some models. Spigot fitting for Sky Minidishes.
"Twin-output" universal LNB
Previously available in Standard (10.0 GHz) and Enhanced (9.75 GHz) form, but now only in "Universal" form (9.75 + 10.6 GHz), the twin-output LNB provides two outputs to feed two separate receivers for independent working.
Each output can be switched independently by 13/17 volt input by the individual receiver to change polarisation and by 22 kHz to change the band.
This type of LNB is sometimes offered with an adapter to fit it to an oval Sky minidish. Beware! It is not designed to focus on an oval dish so its performance when the signal is compromised by bad weather will not be optimal.
"Duo LNB" or "Monobloc LNB" or "Dual LNB"
Comprises two universal LNBs fixed together at a small angle in a single housing. Only one "F" connector is used. A single coaxial cable connects to the Digital (or Digital + Analogue) receiver which must be able to use DiSEqC signalling to select which LNB is to be used. A "Monobloc" (or "Monoblock") is normally used on an 80 cm dish to receive Astra at 19.2'E and Hotbird at 13'E (but not simultaneously).
A double LNB called a "Duo LNB" will usually be for reception of Astra 23.5°E and Astra 19.2°E.
Monobloc set-up Monobloc setting up
This type of LNB has a single output and the actual satellite signal is selected by the receiver which sends a DiSEqC (22 kHz) pulsed tone up the LNB cable. So only one satellite transmission can be viewed at a time. This is in contrast with dish systems that have two or more separate LNBs where, with two receivers, both satellite transmissions can be viewed or recorded simultaneously. See picture HERE. Not compatible with a Sky Digibox. Not usually suitable for fitting to a Sky minidish (although it can be done - but expect poor performance in bad weather)."Quad-output" or "Quad universal" LNB
This universal LNB can feed four separate receivers. Each receiver has independent control of polarisation and band via 13/17v switching and 22 kHz o/off respectively.
This LNB is used with the new Sky Digiboxes and Freesat receivers that have two LNB inputs and internal Hard Drives for recording a programme while you watch another. Two LNB outputs go to this "Sky Plus" Digibox (or Freesat+) and the other two LNB outputs can go either to two standard Digiboxes or to one other "Sky Plus" (or Freesat+) Digibox. As illustrated, this LNB is not suitable for use with a Sky minidish. The Sky minidish version has a spigot fixing. "OCTO" universal LNB
As above but with eight independent outputs. We stock a Sky minidish "spigot" version and a standard (40 mm neck) version. The latter works well with a 60 cm dish in the UK.
"Quattro" universal LNB
This has four fixed outputs and is used only in "head end" I.F. distribution systems (or "multiswitch") for apartment blocks. One LNB supplies a head end unit that can provide (typically) up to 16 outputs for separate Digiboxes. The four outputs of the LNB are as follows:-
1. Horizontal polarisation low band 2. Horizontal polarisation high band 3. Vertical polarisation low band 4. Vertical polarisation high band
You should not connect any of the Quattro outputs, 1 - 4, directly to a receiver (except for testing purposes) unless you want to restrict viewing to just one of the four band options. Even if you do, the receiver may not work. If you simply need four or eight outputs, use the Quad or OCTO instead. No Quattro is manufactured to fit a Sky minidish. It always requires a (roughly) circular dish. Click HERE to see a suitable dish for England.
If you "mix 'n' match" by picking a 60 cm dish and a Universal LNB at random, the chances are that the performance could be no better than that of the Sky minidish.
As a general rule, any standard LNB will work with a circular (prime focus) dish or an offset focus dish which is taller than it is wide (which "looks" circular when viewed by the LNB).
There are some exceptions: a dish optimised to hold more than one LNB may be an "odd" shape. Some dishes are oddly shaped for mainly aesthetic purposes.
However, a dish which is considerably wider than it is tall (as viewed by the LNB) will need a special LNB for optimum performance. A "Sky minidish" LNB is suitable for a wide oval dish.
Just to prove the point, here is a very early type of "Universal" LNB used with a Sky "minidish" (no longer manufactured).
The minidish is oval in shape, being much wider than it is high.
Inside that plastic rain cover is the actual LNB. Note the difference in scalar ring height (red arrows). The side projections allow the LNB to focus on a wide area in the horizontal plane, while the top and bottom projections are longer and focus the LNB on a narrower area in the vertical plane. This LNB is designed specifically for an oval dish and will give very poor results with a dish that is roughly circular or a dish that is taller than it is wide.
Here's another comparison. The SX1019 on the left has circular scalar rings inside the feed horn. It is designed to be used with a nearly circular dish.
The SX1019/S on the right is designed specifically for a Sky minidish which is wider than its height. This type of LNB can also be used with a Raven dish of a similar shape to the Sky minidish.
Both LNBs are made by Philips. The one on the right, however, is branded "Skyware".
Sky "Minidish" upgrades
Here is an obsolete Philips SC519QS/S Quad output LNB, which used to be supplied with the SKY-plus system with adapters for the "minidish". The red arrow points to the special oval shaped "scalar" steps in the feed horn. These cause the LNB to focus exactly on the oval shape of the "minidish", using the full dish area but without picking up reflections from the wall behind. This type of LNB would not give good results with a circular dish.
Some dealers are offering a standard Twin-output or Quad output LNB with an adapter to fit the "minidish". The adapter fits a treat. Unfortunately, the LNB will not give optimum performance - and could give "rain dropout" during bad weather.
(We can supply an adapter to fit a 40 mm LNB to a Sky minidish but you use it at your own risk).
However, you may prefer to buy a standard dish of, say, 60 cm diameter and use a standard 40 mm neck twin-output or quad-output LNB with this. The match and fitting will be perfect and the "rain dropout" will be very rare.
If you are fitting a Quad-output or OCTO LNB to your dish, read this page.
The LNB, above, has a spigot which fits into the Sky minidish arm. The LNB rotational position or "skew" can be adjusted by slackening the two screws that secure the spigot and twisting the LNB until best signal quality is achieved.
The LNB on the left has a single screw but the principle is the same. A Sky LNB will often have graduated marks from 1 to 5 as a guide to alignment. Start at 3 and twist each way to locate the best position.