Editing Low-noise amplifier (section)

== Communications ==
[[Antenna (radio)|Antennas]] are a common source of weak signals.<ref>{{Cite book|title = A 900MHz Low Noise Amplifier with Temperature Compensated Biasing|url = {{google books |plainurl=y |id=GynLjAaZX8EC}}|date = 2008-01-01|isbn = 9780549667391}}</ref> An outdoor antenna is often connected to its receiver by a [[transmission line]] called a ''[[feed line]]''. Losses in the feed line lower the received signal-to-noise ratio: a feed line loss of {{val|3|u=dB}} degrades the receiver signal-to-noise ratio (SNR) by {{val|3|u=dB}}.

An example is a feed line made from {{convert|10|feet|m}} of RG-174 [[coaxial cable]] and used with a [[global positioning system]] (GPS) receiver. The loss in that feed line is {{val|3.2|u=dB}} at {{val|1|ul=GHz}}; approximately {{val|5|u=dB}} at the GPS frequency ({{val|1.57542|u=GHz}}). This feed line loss can be avoided by placing an LNA at the antenna, which supplies enough gain to offset the loss.

An LNA is a key component at the front-end of a [[radio receiver]] circuit to help reduce unwanted noise in particular.  [[Friis formulas for noise|Friis' formulas for noise]] models the noise in a multi-stage signal collection circuit. In most receivers, the overall NF is dominated by the first few stages of the [[RF front end]].

By using an LNA close to the signal source, the effect of noise from subsequent stages of the receive chain in the circuit is reduced by the signal [[Gain (electronics)|gain]] created by the LNA, while the noise created by the LNA itself is injected directly into the received signal. The LNA boosts the desired signals' power while adding as little noise and distortion as possible. The work done by the LNA enables optimum retrieval of the desired signal in the later stages of the system.