| 摘要 |
PURPOSE:To enhance the stability of a filter characteristic, to reduce the number of adjusting places and to increase a detection speed, in a spectrum analyzer according to a heterodyne system, by digitalizing BPF determining frequency resolving power. CONSTITUTION:An input signal containing a large number of frequency components after passing through BPF 30, wherein the band width of the final stage circuit among circuits of multistage mixers and BPFs is fixed and constitution is simple, is applied to an amplifier 32 having a wide dynamic range and processed by mixers 40, 41 to which oscillation outputs different by 90 deg. in a phase are supplied from an oscillator 38. The outputs of these mixers 40, 41 are processed by low-pass filters (LPF) 43, 44 and A/D converters 46, 47 to be supplied through digital filters 50, 51 and subjected to double sum processing by an operator 53 to become a predetermined frequency spectrum signal. By bringing this BPF determining frequency resolving power to digitalized constitution, the stability of a filter characteristic due to temp. or the elapse time is enhanced and a required narrow band can be easily realized and the number of adjusting places are reduced and a detection speed is enhanced.
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