What is an LNB?

What is an LNB?
Low Noise Block-downconvertor (so called because it converts a whole band or "block" of frequencies to a lower band).

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.

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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 suitable dish, align the dish and LNB 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, the reverse is not true. If some channels appear to be missing, this could be the fault of the cable, the receiver or the dish (distorted or misaligned). It does not prove that the LNB is faulty. 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).

Can't I test it with a meter?

A cheap satfinder meter 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.



List of Universal LNB types:


The 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 40mm neck but C120 flange type available in some models. Spigot fitting for Sky Minidishes.

A Universal LNB requires a 22kHz signal at 0.5v p-p to switch its Local Oscillator to 10.6GHz ("high band"). Otherwise it uses its 9.75GHz oscillator ("low band").

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 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.

"Twin-output" LNB
Currently available in Standard, Enhanced and Universal form, 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 22kHz to change the band.

"Dual LNB" or "Monobloc 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. Normally used on an 80cm dish to receive Astra at 19.2'E and Hotbird at 13'E (but not simultaneously).

This type of LNB has a single output and the actual satellite signal is selected by the receiver which sends a DisEqC (22kHz) 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.

"Quad-output" or "Quad universal" LNB
This can feed four separate receivers. Each receiver has independent control of polarisation and band via 13/17v switching and 22kHz o/off respectively. This LNB is used with the new Sky Digiboxes 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 and the other two LNB outputs can go either to two standard Digiboxes or to one other "Sky Plus" Digibox.

"OCTO" LNB
As above but with eight independent outputs.

"Quattro universal LNB"
This has four fixed outputs and is used only in "head end" I.F. distribution systems 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 outputs, 1 - 4, directly to a receiver unless you want to restrict viewing to just one of the four options. Even if you do, the receiver may not work. It's not a good idea. Use the Quad instead.

If you "mix 'n' match" by picking a 60cm 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).

However, a dish which is wider than it is tall will need a special LNB.


Just to prove the point, here is a typical "Universal" LNB used with a Sky "minidish".

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 feedhorn. 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 the Philips SC519QS/S Quad output LNB as supplied with the SKY-plus system with adaptors for the "minidish". The red arrow points to the special oval shaped "scalar" steps in the feedhorn. 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.

Some dealers, who are either unscrupulous or simple know no better, are offering a standard Twin-output or Quad output LNB with an adaptor to fit the "minidish". The adaptor fits a treat. Unfortunately, the LNB will not give optimum performance - resulting in "rain drop-out" during bad weather.

Although the Philips SC519QS/S Quad output LNB kit *is* available, it is rather expensive. If you *must* use the "minidish" (and there are good aesthetic and environmental reasons to do so) then you'll have to pay the price.

However, you may prefer to buy a standard dish of, say, 60cm diameter and use a standard 40mm neck twin-output or quad-output LNB with this. The match and fitting will be perfect and the "rain drop-out" will be very rare. The price of a 60cm dish with twin-output LNB will be less than that of a Philips SC519QS/S Quad output LNB kit .
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