An LNB or low-noise block converter (sometimes called LNC) is the antenna used for communications satellite TV reception. It is usually attached on or in the satellite dish. Although LNB is waveguide-based, it functionally corresponds to a dipole antenna used for majority of TV reception purposes.
While the dipole antenna is not able to settle in various polarization planes without rotating, the LNB can be electronically changed between vertical and horizontal polarization reception. Its satellites utilize relatively high radio frequencies to send their signals.
Function of LNB
LNB is used to employ the super heterodyne effect, augment a wide band (or block) of frequencies, and convert them to signals transmitted at a much lower intermediate frequency.
The intermediate frequency would travel through cables with less reduction of the signal, so there are more signals for the receiver of the cable.
Developing electronic circuits to work at these lower frequencies instead of operating at very high frequencies is easier and less expensive. This also assists in compensating for lost signal because of typical coaxial cable at comparatively high frequencies.
Features of LNB
The term ‘low noise’ is related to the feature of the special engineering used – the 1st stage of the input amplifier transistor. This is measured in Noise Figure Units, Noise Factor Units, or Noise Temperature Units. Low noise also means that mixing and amplification happen before the cable attenuation in a circuit that does not require a power supply or receiver.
Both Noise Figure and Noise Factor are easily converted into Noise Temperature Units. A lower rating in the Noise Temperature is always better.
The word “block” describes the change of a superior block of microwave frequencies to the receiver’s inferior block range of microwave frequencies.
The low-noise block converter helps keep the overall picture and audio of the satellite TV from being degraded. This is done without having to introduce a much larger dish reflector.
For wide bandwidth satellite TV transporter signal, the accuracy of the local oscillator frequency of the LNB has to be more or less 500KHz. This would make an economical dielectric oscillator (DRO) viable.
However, for reception narrow band satellite television carriers, a low-phase noise and highly stable local LNB oscillator is needed.