LNBs in Spain, Low Noise Blocks LNBs
An LNB is a device mounted on the dish, designed collect and amplify the satellite signals and convert them from a high frequency to a lower frequency. LNBs can be controlled to receive signals with different polarisation (horizontal and vertical). The signals can then be carried down the cable cable to a satellite receiver.
An LNB can be either single (one output), Twin (two outputs), Quad (four outputs), Quatro (four outputs), or Octo (eight outputs).
A Twin LNB would be required when more than one receiver (or a PVR like Sky+) is used allowing the viewing of different channels on two independent satellite receivers.
A Quad LNB would be required when more than three receivers.
A Quatro LNB would be required when requiring to install a multiswitch system that can provide feeds for many receivers, as in the case of a community system installation.
Here is an example of a Universal LNB for smaller 80cm offset dishes.
Invacom Offset LNB Single SNH-031 LNB 0.3dB C120
Here are examples of the Invacom LNBs used for Prime Focus big dish installations.
A monobloc LNB (also spelled “monoblock”) is a unit consisting of two LNBs and is designed to receive satellites spaced close together, generally 6 degrees. For example in parts of Europe monoblocs designed to receive the Hot Bird (13E) and Astra 1 (19E) satellites are popular because they enable reception of both satellites on a single dish without requiring an expensive and noisy motor.
Low noise block converters operate in extremes of temperature and humidity, and although they generally have a very low failure rate they do not last forever. Some fail as they get older, others suffer a drop in performance, resulting in poor picture quality.
Some LNBs, particularly the Invacoms mentioned above require a feedhorn preferably one from the manufacturer of the LNB, has to be attached to the LNB.
The most common type of feedhorn manufactured today is called a scalar feedhorn. This type of feed has a large circular plate with a series of three or four concentric rings attached to its surface. The scalar rings conduct the incoming signal from the outer edges of the focal cloud to the large waveguide opening located at feed centre. The scalar feedhorn primarily sees or illuminates the inner portion of the antennas surface area, while attenuating the signal contribution from the outer portion of the dish by 8 to 22 dB, depending on whether the dish is deep or shallow in its construction.
Inline amplifiers will not increase your weak Astra 2D signals, in fact they will probably reduce your signal. An Inline Amplifier should be used when the cable run from the LNB to the receiver exceeds 75 – 100 feet; install the amplifier between the LNB and the Multiswitch or satellite receiver.
Inline amplifiers are powered by the voltage already present on the satellite signal coax. If your signal is not strong enough in the first place, you are really only amplifying noise. An Inline amplifier is unfortunately of little or no use when trying to increase a weak signal, it will also ‘boost’ stronger signals swamping your already weak signal. A better LNB or larger dish will give far better results.
LNB Skew Alignment
The LNB on the end of the satellite dish picks up either a horizontal or a vertical signal. Your satellite receiver sends an 18volt current to the LNB when it requires a horizontal signal and a 13volt current for a vertical signal.
For satellite reception, the ‘skew’ angle of the LNB is also important. The ‘skew’ angle represents the horizontal/vertical plane of the LNB. When a satellite dish is facing towards a satellite at due South, the plane of the LNB will be vertical (straight down). As the dish is moved around either East or West to receive other Satellites the LNB will need to be tilted (rotated), clockwise for West and counter clockwise for East.
As you travel around Europe, the correct skew position of the LNB changes very slightly.
The LNB skew angle needs to be set correctly for the LNB to differentiate between horizontally and vertically polarized signals. If the LNB skew is wrong then you may not be able to obtain some channels.
The main effect of the LNB being out of Skew is a reduction in the “Signal Quality”. The easiest way to make adjustments with out a spectrum analyser is to slightly adjust the LNB and then check the satellite signal quality reading on your Sky or Freesat box.
On the Costa Blanca an incorrectly skewed LNB can result in the loss of the weaker North beam frequency transponders on Astra 2A and Astra 2B. A well done installation will ensure that the LNB skew is correct so that the North beam channels are not loss or loss is kept to a minimum.
An incorrect skew angle on the LNB can also result in the Sky Signal test screen showing no or little Signal Strength or Signal Quality – as this screen on the Sky digibox is measuring the 11778 North beam satellite frequency frequency – and being a north beam satellite frequency the LNB skew is critical.
An example of an LNB at the wrong skew angle. I was called to this dish, installed by another satellite installation company, as the clients were not receiving the same channels as their neighbours whose dish I had installed.
Ideally the LNB skew for the Costa Blanca for the UK TV channels on the Astra 2 satellites should have the bottom of the LNB, where the cables area, at an angle of about 7 o’clock. Not a 9 o’clock. This meant that the UK TV channels were not being received.