Spectrum analyzers and signal analyzers are passive receivers, which displays the signal in the form of easily identifiable data.  Spectrum analyzers and signal analyzers display raw, unprocessed signal information such as voltage, power, period, wave shape, sidebands, and frequency. They can provide the user with a clear and precise window into the frequency spectrum. Spectrum analyzers and signal analyzers are used to analyze the electrical signals that are passing through or being transmitted by the system or device.  They are widely used in situations where design, manufacturing and field service or repair of electrical systems or devices is needed. By analyzing the characteristics of the signal once its gone through the device / system, the user can determine the performance, find problems, troubleshoot, etc. Depending upon the application, a signal could have several different characteristics. For example, in communications, in order to send information such as voice or data, it must be modulated onto a higher frequency carrier. A modulated signal will have specific characteristics depending on the type of modulation used. When testing nonlinear devices such as amplifiers or mixers, it is important to understand how these create distortion products and what these distortion products look like. Understanding the characteristics of noise and how a noise signal looks compared to other types of signals can also help in analyzing the device/system.