A RF mixer is an electronic device used for changing a signal from one frequency range to another frequency range. As the name suggests, it works by mixing two signals together, usually one at a very high frequency and the other at a low frequency. The output is often in a third frequency range which is the sum of the two inputs. The process of mixing two signals is also known as heterodyning. RF mixers can be used to either increase or decrease the frequency of an incoming signal, allowing it to be shifted to a different range as required. They are commonly used in telecoms infrastructure, satellite communications, radio receivers and transmitters, and medical instruments.