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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.

Physical Specifications

Important physical specifications to consider when searching for spectrum analyzers and signal analyzers include mounting and form factor.  Choices include handheld, portable or benchtop, and fixed.  The analyzer is usually an instrument based unit or pc-based unit.  Test types performed by analyzers include modulation, distortion, and noise.  Measuring the quality of the modulation is important for making sure a system is working properly and that the information is being transmitted correctly. In communications, measuring distortion is critical for both the receiver and transmitter.  Excessive harmonic distortion at the output of a transmitter can interfere with other communication bands. Because any active circuit or device will generate noise it is an important parameter to measure.  Tests such as noise figure and signal-to-noise ratio (SNR) are important for characterizing the performance of a device and/or its contribution to overall system noise.  Analysis types include fast Fourier transform (FFT) and swept-tuned.  The Fourier analyzer basically takes a time-domain signal, digitizes it using digital sampling, and then performs the mathematics required to convert it to the frequency domain, and display the resulting spectrum.  It is as if the spectrum analyzers and signal analyzers are looking at the entire frequency range at the same time using parallel filters measuring simultaneously. The most common type of spectrum analyzer is the swept-tuned receiver.   It is the most widely accepted, general-purpose tool for frequency-domain measurements. 

Frequency Performance Specifications

Important frequency performance specifications to consider when searching for spectrum analyzers and signal analyzer include the frequency range, frequency accuracy, and frequency resolution.  It is important that a spectrum analyzer will cover the fundamental frequencies of the application, as well as harmonics or spurious signals on the high end, or baseband and IF on the low end. Frequency accuracy is often listed under the Frequency Readout Accuracy specification and is usually specified as the sum of several sources of errors, including frequency-reference inaccuracy, span error, and RBW center-frequency error. Resolution is an important specification when trying to measure signals that are close together and need to be distinguishable from each other.  The IF filter bandwidth is also known as the resolution bandwidth (RBW).  Input and output specifications to consider include number of input channels, dynamic range, and number of output channels.

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