This application note is part of a series about noise measurement. Much of what is discussed is either material that is common to most noise figure measurements or background material. It should prove useful as a primer on noise figure measurements. The need for highly repeatable, accurate and meaningful measurements of noise without the complexity of manual measurements and calculations has lead to the development of noise figure measurement instruments with simple user interfaces. Using these instruments does not require an extensive background in noise theory. A little noise background may prove helpful, however, in building confidence and understanding a more complete picture of noise in RF and microwave systems.