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FFT display on the WBT-200

Question

In FFT-based (digital) spectrum analyzers, RBW is inversely proportional to the number of samples acquired. By taking more samples in the time domain, or making the acquisition time longer while keeping the sampling rate the same, the signal's resolution is lowered. The result is more bins in the same span and improved viewing/recording of frequency resolution. Given the 12bit A/D converter and the WBT's FFT bin size/digital stack, what is the smallest frequency we can display, or the smallest frequency that can be resolved and captured within a selected bandwidth?

 

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The current software (2.3.1.35) provides a RBW that is BW/1024.  A bandwidth of 40 MHz will have a display RBW of about 39 kHz.  In the next major release the display RBW will be adjustable.

What's recorded is complex time data which is unaffected by the RBW setting.  Some of a data stream (typically < 1%) is used for a trace display.

In general, a data stream from a digital tuner or the data drive is available to an embedded application so we can do whatever is required to generate the display information needed.

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Smallest frequency that can be resolved and captured by any radio depends on the frequency stability (e.g. frequency accuracy and frequency jitter) of the radio.

With large enough size of the FFT used, this smallest frequency can also be displayed.

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