Resolution Bandwidth Calculator

This tool calculates the Resolution Bandwidth (RBW) of a Spectrum Analyzer based on

  • Frequency Span
  • Number of FFT points (N)

	

			

		

						

				

				

                

			

			
						

		

		






Formula





RBW = Span/N





Background





Most spectrum analyzers are built with super-heterodyne receivers. The final stage of such receivers have a bandpass filter. This is also called an Intermediate Frequency (IF) Filter. 





In older spectrum analyzers the resolution bandwidth (RBW) was determined by the bandwidth of the IF filter. In newer FFT based spectrum analyzers, the RBW depends on the number of digital samples used to compute the FFT and the Span. 





In older spectrum analyzers, RBW = IF bandwidth. 





In newer FFT based analyzers, RBW < IF bandwidth.





💡 The RBW determines the frequency resolution of the resulting spectrum. The smaller the RBW, the higher the spectral resolution. The larger the RBW, the easier it is for signals that are close in frequency to be combined. The smaller the RBW, the easier it is to tell them apart. As well, a smaller RBW increases the sensitivity of the analyzer to capture weaker signals. 





When performing a scan across a specified frequency range, the sweep time and speed are affected by the RBW setting. The smaller the RBW the longer the sweep time. 





In summary, a smaller RBW will help discern closely spaced and weak signals but the extended sweep time can reduce the likelihood of capturing time varying signals. 





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