How does a real-time spectrum analyzer work?

1. Parallel filter type real-time spectrum analyzer (real-time spectrum analyzer)

The shunt filter spectrum analyzer is a true real-time spectrum analyzer.

After the measured signal is amplified by the bandwidth, it is sent to multiple band-pass filters by the demultiplexer. Each filter selects the required spectrum component from the signal to be measured, and after the detector detects the signal, it sends it to each monitor and keeps the display. . In designing and manufacturing such a real-time spectrum analyzer, the center frequency of each filter is tuned to different frequencies within the spectrum. This requires that the bandpass of the filter is narrow, the characteristic curve of the filter is close to a rectangle, and each filter is The bandpass frequency range of the device should be properly overlapped. The spectrum analyzer can cover the entire frequency range, and any spectral component in the measured signal is not missed, and different frequency components in the measured signal can be displayed on different displays. In this way, the spectrum distribution of the measured signal at this moment is indicated on each display. The advantage of this type of analyzer is that all the filters are connected to the input signal under test at all times and can instantaneously detect and display transient, uncertain signals with fast measurement speeds, wide dynamic range and amplitude measurement accuracy. Advanced, its disadvantage is that the operating frequency range is low, about 100KHz, because the number of discrete spectrums that the analyzer can display depends on the number of filters, and the resolution bandwidth of the real-time spectrum analyzer depends on the bandwidth of the filter. It is conceivable that the frequency range covers 100 KHz and a real-time spectrum analyzer with a resolution of 1 KHz requires 100 filters and displays. This shows that the price of such a real-time spectrum analyzer is very expensive. A typical shunt filter is a real-time spectrum analyzer. Sampling 32 filters to compromise cost and resolution.

2. Fast Fourier Transform (FFT) Real-Time Spectrum Analyzer

The fast Fourier transform algorithm can convert the time function f(t) at a certain moment into the frequency function s(w).

In the FFT real-time spectrum analyzer, the time domain is used to sample the measured signal. After high-speed A/D conversion and fast Fourier analysis, not only can the amplitude-frequency function be determined, but also the phase-frequency function can be determined. In order to obtain the frequency, amplitude and phase information of the measured signal, it is possible to perform frequency domain analysis on non-periodic signals and transient signals.

One of the advantages of the FFT real-time spectrum analyzer is the ability to quickly capture and analyze single-shot signals for transients that the spectrum analyzer cannot capture. Another advantage is the ability to measure amplitude and phase. The disadvantage is that the FFT real-time spectrum analyzer is limited by the A/D conversion sampling rate. Due to the rapid development of technology, its A/D and sampling rate have greatly improved. Many manufacturers have also launched their own real-time spectrum analyzers; : Keysight's RTSA Series Real-Time Spectrum Analyzers, R&S's FSVR Series Real-Time Spectrum Analyzers, TEK's RS Series Real-Time Spectrum Analyzers, Signal Hound Portable Real-Time Spectrum Analyzers, Andoni's Handheld Real-Time Spectrum Analyzers, Mike Nice handheld real-time spectrum analyzer, etc.; real-time bandwidth is even up to 200MHz.