Spectrum refers to the total set of all frequency components that make up the signal
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Measuring the signal in the frequency domainfrequencyComponent to obtain multiple parameters of the signal and parameters of the network through which the signal passes.Although the spectrum measurement belongs to the scope of electronic measurement, in addition to the analysis and research of electrical signals, it can also use various sensors or converters to measure various non electrical signals (underwater sound, vibration, biologyMedical Science, various random processes and transient processes such as explosion, missile launch, underwater acoustic reverberation, ship andtorpedoNoise, etc.) to improve its design.
Chinese name
Spectrum measurement
Measurement method
Sweep frequency type, real-time type
Interpretation
Spectrum refers to the total set of all frequency components that make up the signal
Spectrum refers to the total set of all frequency components that make up a signal.In general spectrum measurement, amplitude spectrum is often called spectrum.From the graph, spectrum can be divided into two basic types. ①Discrete spectrum: also called linear spectrum, the figure is linear, and there is a certain interval between each spectral line (the line representing the amplitude of a frequency component).The spectrum of periodic signal is discrete spectrum, and the interval between each spectral line is equal to the fundamental frequency or integral multiple of the periodic signal. ②Continuous spectrum: the interval between the spectral lines is infinitesimal, and the spectral lines are connected into one piece.The spectrum of aperiodic signals and various irregular noises is continuous spectrum, that is, there are signal spectral lines on all frequencies within the observed frequency range.The actual signal spectrum is often mixed spectrum. The measured continuous signal or periodic signal, in addition to the discrete spectrum presented by its fundamental frequency, harmonics and parasitic signals, is inevitably accompanied by the continuous spectrum presented by random thermal noise as the base.
The basis of spectrum measurement is Fourier transform.It can transform a signal that changes with time into a function of the frequency associated with the signal.Therefore, any time-varying signal can be decomposed into sine waves with different frequencies, phases and amplitudes.
Measurement method
Announce
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There are two methods for spectrum measurement: sweep frequency method and real-time method. ①Sweep frequency type: frequency spectrum measurement of repeated signals is completed through multiple frequency conversion processes based on the principle of swept superheterodyne reception.The characteristic of this method is that the local oscillator sweeps in a wide frequency band while the receiver is narrowband, so only one frequency component in the signal is measured at any moment (the receiver filter has a certain bandwidth, and the circuit needs a certain response time, so each spectral line actually occupies a fixed frequency band), and the other frequency components are suppressed.As the local oscillator sweeps, measure the remaining frequency components in the signal in sequence.This method is only applicable to the spectrum measurement of continuous signals and periodic signals, and can not measure the phase of signals. ②Real time: all required spectrum information can be obtained within the actual time when the measured signal occurs, and the measurement results can be displayed.This method is characterized by using modern digital circuit technology and computer technology to quickly sample and analog-to-digital transform the signal, and then performing correlation processing with the orthogonal local oscillator that generates sine and cosine signals in the digital filter, and storing and displaying the measurement results after integral operation.This method is especially suitable for the spectrum measurement of non repetitive signals, stationary random processes and transient processes with short duration, as well as the spectrum measurement of periodic signals, and can measure the phase of signals.However, due to the limitation of sampling time and digital analog conversion speed in digital circuit technology, this method can only measure the spectrum of signals below 40 MHz at present.
