In the field of physics, the information contained in a signal is obtained by measuring its waveform, duration, or amplitude, frequency, and phase parameters of each frequency component, such as the structure, purity, and characteristics of the channels (transmission lines and network systems) through which the signal passes, also known as signal analysis There are two methods for signal analysis: time-domain method and frequency-domain method. They are two different expressions of the same process, mathematically a pair of Fourier transform expressions. Time domain analysis studies the law of signal amplitude changing over time, namely waveform analysis. Electronic oscilloscopes (including sampling oscilloscopes and memory oscilloscopes) are the most ideal instruments for waveform analysis, capable of intuitively measuring and recording signal amplitude changes, waveform distortion, frequency, phase shift, and other non sinusoidal waves. Although the measurement accuracy is slightly poor, in signal waveform measurement, especially when measuring the duration, leading and trailing edge time, overshoot, and other characteristics of pulse signals, it is simpler and more accurate to directly use the time-domain method, and the results are also more accurate. The principle of frequency domain measurement is to use a narrowband filter to measure the amplitude of each frequency component in the signal, and the measurement results can be displayed using an electric meter, oscilloscope tube, or digital display element. A frequency sweep local oscillator can be used to convert the signal, allowing each frequency component to sequentially pass through a narrowband filter with a constant center frequency to measure the amplitude; Narrowband filter banks with interconnected central frequencies can also be used to measure the frequency component of the signal. Signal analyzers that utilize the above frequency selection principles include frequency level meters, frequency voltage meters, field strength meters, spectrum analyzers, distortion meters, modulation meters, and Fourier analyzers. The frequency selection level meter and frequency selection voltage meter are composed of a highly sensitive superheterodyne receiver, which uses an intermediate frequency filter with sharp frequency characteristics to change the local oscillator frequency and thus the frequency selection frequency of the voltage meter. However, the bandwidth remains unchanged, and an ammeter is used to indicate the signal level or voltage The instrument field strength meter is a highly sensitive superheterodyne receiver with standard antennas (ring type, double dipole type, logarithmic periodic type, etc.), which can measure the absolute strength of the electric field or signal strength at the receiving point. Spectrum analyzer is a multi-purpose signal analyzer that uses an oscilloscope tube to display the amplitude of each frequency component of the signal in the frequency domain (x-axis), forming a spectrum graph of the signal. The distortion meter determines the purity of a sine signal by measuring its harmonic content. Distortion is the ratio of the effective value of the harmonic voltage of a signal to the effective value of the fundamental voltage. In practice, the ratio of the effective value of all harmonic voltage to the effective value of the signal voltage is used to simplify the technology and have little impact on accuracy. The modulation meter consists of a precision receiver, and its intermediate frequency bandwidth must include the entire spectrum of the modulated signal to detect the frequency and power of the carrier, as well as the amplitude, frequency, and maximum frequency offset of the modulated wave. According to the definition of modulation depth, the modulation index, and residual modulation values are directly indicated after conversion. The Fourier analyzer uses digital processing technology to filter signals and eliminate out of band noise. Every time a signal is sampled, the time-domain function of the signal is transformed into frequency-domain data using the Fast Fourier algorithm, recorded in memory, and can be displayed on the fluorescent screen at any time