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== What is an Amplifier? ==
An amplifier (aka amp) is an electronic device that can increase the power of a signal. An amplifier uses electric power from a power supply to increase the amplitude of a signal. The amount of amplification provided by an amplifier is measured by its gain: the ratio of output voltage, current, or power to input. An amplifier is a circuit that has a power gain greater than one.
[[File:Amplifier1Amplifiers7.png|frame|center|Amplifier basic diagram - (a) A voltage amplifier fed with a signal V(t)(b) Transfer characteristics of linear voltage amplifier. Inspired from Sedra and Smith]][[File:Amplifiers8.png|frame|center]]An amplifier is an electrical two-port network that produces a signal at the output port that is a replica of the signal applied to the input port, but increased in magnitude. There are various types of amplifiers, some can change the phase of the input signal, some can cause distortion. According to what an amplifier does to input signal, they are divided into various classes. Amplifier Classes represent the amount of the output signal which varies within the amplifier circuit over one cycle of operation when excited by a sinusoidal input signal.
* Class A - 360° conduction
* Class B - 180° conduction
It is not always possible to increase the transmission power indefinitely such that every receiver can get the required power of the signal. Especially in satellite communication there is a constraint in the transmission power as the solar panels produce a fixed amount of power (For further details read [[Power Budget]]). One method that can be used is to amplify the signal at the receiver end. After the signal is capture by the antenna, we can amplify the signal using a amplifier. After amplification the signal is filter, this process if called conditioning of the signal. After conditioning the signal can be demodulated and interpreted. This amplifier is called as Low Noise Amplifier (LNA). <br \>
Amplification of signal is the first step in receiving process while is the last in transmission process. You can see this in the following diagram. Generally amplifiers are represented using a triangle. In the figure HPA - High Power Amplifier and LNA - Low noise amplifier. You can see that in both, the amplifier are connected to the antenna.
[[File:Amplifier2Amplifiers4.jpgpng|framethumb|center|1000px| Satellite Communication Link Block Diagram. Inspired from [https://about.keysight.com/en/newsroom/backgrounders/FieldFoxsatellite/ here]]]
==Some parameters related to amplifiers ==