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Introduction of Spectrum Analyzer

Spectrum analyzer is an instrument to study the spectrum structure of electrical signals. It is used to measure signal parameters such as signal distortion, modulation, spectral purity, frequency stability and intermodulation distortion. It can be used to measure some parameters of circuit systems such as amplifiers and filters. 

It is a multi-purpose electronic measuring instrument. It can also be called frequency domain oscilloscope, tracking oscilloscope, analytical oscilloscope, harmonic analyzer, frequency characteristic analyzer or Fourier analyzer. Modern spectrum analyzer can display the analysis results in analog or digital way, and can analyze all radio frequency bands from VLF to sub-millimeter wave bands below 1 Hz. 

If the digital circuit and microprocessor are used in the instrument, it has the function of storage and operation, and the standard interface is configured, it is easy to form an automatic test system.

The main function of the spectrum analysis system is to display the spectrum characteristics of the input signal in the frequency domain. There are two types of spectrum analyzer, Real-Time Spectrum Analyzer and Sweep-Tuned Spectrum Analyzer, according to different signal processing methods. The function of real-time frequency analyzer is to display signal amplitude in frequency domain at the same instant, and its working principle is different. 

The corresponding filter and detector (Detector) transmit the signal to CRT or LCD display instrument through synchronous multiplex scanner. Its advantage is that it can display the instantaneous response of periodic Random Waves. 

Its disadvantage is that it is expensive and its performance is limited to the bandwidth range and the number of filters. The most commonly used spectrum analyzer is the scanning tuned spectrum analyzer. Its basic structure is similar to the superheterodyne receiver. Its working principle is that the input signal is directly added to the mixer through the attenuator, and the tunable local oscillator is generated over time by the scanning generator synchronized with CRT. The frequency of oscillation varies linearly, and the IF signal is amplified after mixing the mixer with the input signal. 

The filter and detection are transmitted to the vertical direction plate of the CRT. Therefore, the corresponding relationship between the signal amplitude and frequency is displayed on the longitudinal axis of the CRT. Lower RBW is helpful to the resolution and measurement of signals with different frequencies. Lower RBW will filter out the components of signals with higher frequencies, resulting in distortion in signal display. 

Distortion value is closely related to the set RBW. Higher RBW is helpful to the detection of broadband signals, increasing Noise Floor and reducing measurement. Sensitivity can easily hinder the detection of low intensity signals, so proper RBW width is an important concept for the correct use of spectrum analyzer.