In lab and workshop the most commonly used signal checks an instrument is electronic oscillograph. The person's thinking is more sensitive to time concept, produce connection with time domain incident all the time, but signal often appears with frequency form, observe with oscillograph signal of the simplest amplitude modulation carrier wave is no-go also, often show to appearance of not clear modulation visits when carrier wave, what obtain on screen is 3 spectral line, namely carrier frequency and the modulation frequency that control in carrier frequency. Modulation pattern is mixedder, electronic oscillograph shows harder, the expressive capability of spectrum analyzer is strong, spectrum analyzer is the delegate of the frequency domain instrument of be worthy of the name. The number of one frequency expresses communication time the method is Fourier commutation, it discloses time signal into sine and the overlay of cosine curve, the signal that finish changes the course of frequency region by time-domain.
Inchoate spectrum analyzer is receiver of a sweep essentially, input signal and signal of this locality oscillation are after first detector frequency conversion, through a group of shunt-wound different centers the belt of frequency connects filter, make input signal to show axis of filter definitive frequency is connected to go up in a group of belts. Apparent, because take a filter to be formed by passive component, spectrum appears very cumbersome on analyzer whole, and frequency resolution is not high. Since Fourier commutation can disclose input signal into the frequency heft of schism, can have the action with similar filter likewise, circuit of fast Fourier commutation replaces have the aid of low connect filter, make of spectrum analyzer form simplify, resolution heighten, measure time to shorten, sweep limits expands, this is the advantage of contemporary spectrum analyzer.
Vector signal analyzer is to be in book frequency limits inside measure circuit gain and corresponding instrument automatically, the sweep frequency cause that it has interior or controllable are exterior signal source. Its function is the gain that surveys pair of circuit be measuringed that input this sweep signal and phasic, its circuit structure and spectrum analyzer are consequently similar. Spectrum analyzer needs to measure the sealed input frequency with random, vector signal analyzer measures oneself only or controlled foregone frequency; The extent that spectrum analyzer measures input signal only (scalar quantity instrument) , the extent that vector signal analyzer measures input signal and phasic (vector instrument) . This shows, the circuit structure of vector signal analyzer is more complex than spectrum analyzer, price is higher also. Contemporary vector signal analyzer also uses fast Fourier commutation, word of the following introduction people similarities and differences.