The HF2 FFT Spectrum Analyzer is a standard feature of all HF2 Instruments, fully integrated inside the ziControl graphical user interface. It builds on a technique also called Zoom FFT, which is the numerical calculation of the FFT spectrum on samples demodulated by the lock-in amplifier. This postprocessing of demodulated samples can be applied to the output of all demodulators inside the HF2 Instruments.
The performance of the HF2 FFT Spectrum Analyzer is amazing, as it delivers an extremely high resolution output compared to an FFT performed on raw data before demodulation. As the resolution of an FFT spectrum is determined only by the total length of time spanned by the samples (and not by the sample rate), it is a numerically challenging calculation if performed on a data stream at high-frequency (it would be 210 MSamples/s for the HF2LI). Instead, if performed on demodulated samples, the length of time can be comfortably increased and the resulting resolution is impressive.
The method applied by the HF2 FFT Spectrum Analyzer is called Zoom FFT as it represents a detailed spectrum on a relatively narrow band signal (after demodulation). In communication technology this method is called multi-rate filtering.
|FFT span window range||0.22 Hz to 460 kHz|
|FFT frequency resolution (minimal)||7 µHz to 14 Hz|
|FFT spectrum plot lines||up to 32'768 lines per plot|
|amplitude accuracy||± 0.2 dB|
|overall phase noise over all carriers||-125 dBc/Hz @ 1 kHz|
|spurious free dynamic range||-80 dB typical|
|display units||VRMS, VRMS^2, Vpk^2, VRMS/VHz, Vpk/VHz, Vrms^2/Hz, Vpk^2/Hz|
FFT Span Window 대 주파수 분해능
Span Window의 선택은 최대 주파수 해상도에 의해 자동으로 결정됩니다.
|FFT Span Window||Minimal Frequency Resolution|
|460 kHz||14 Hz|
|100 kHz||3 Hz|
|10 kHz||300 mHz|
|1 kHz||30 mHz|
|100 Hz||3 mHz|
|10 Hz||300 µHz|
|1 Hz||30 µHz|
|0.22 Hz||7 µHz|