Editing Low-noise block downconverter (section)

==Amplification and noise==
The signal received by the LNB is extremely weak and it has to be amplified before downconversion. The [[low-noise amplifier]] section of the LNB amplifies this weak signal while adding the minimum possible amount of noise to the signal.

The low-noise quality of an LNB is expressed as the [[noise figure]] (or sometimes [[noise temperature]]). This is the signal-to-noise ratio at the input divided by the signal-to-noise ratio at the output. It is typically expressed as a [[decibels]] (dB) value. The ideal LNB, effectively a perfect amplifier, would have a noise figure of 0&nbsp;dB and would not add any noise to the signal. Every LNB introduces some noise but clever design techniques, expensive high-performance low-noise components such as [[High-electron-mobility transistor|HEMT]]s and even individual [[tweaking]] of the LNB after manufacture, can reduce some of the noise contributed by the LNB's components. Active cooling to very low temperatures can help reduce noise too, and is often used in scientific research applications.

Every LNB off the production line has a different noise figure because of [[Engineering tolerance|manufacturing tolerances]]. The noise figure quoted in the specifications, important for determining the LNB's suitability, is usually representative of neither that particular LNB nor the performance across the whole frequency range, since the noise figure most often quoted is the ''typical'' figure averaged over the production batch.
[[Image:Universal-euro-sat-lnb.jpg|thumb|right|120px|K<sub>u</sub>-band linear-polarized LNBF]]