The averaging can be exponential or linear.

• Exponential Averaging is comparable to a low-pass time filtering of the spectrum. In other words each spectral line is low-pass filtered so that the resulting spectrum is smoothed out over time. In that case the Nb_Avg represents an equivalent averaging time constant, expressed in number of successive spectra. The averaging is continuous and does not stop. Each successive spectrum is taken into account in the calculation. A larger value of Nb_Avg produces a spectrum that is more stable, but also averages-out short-lived transients.

• Linear Averaging takes an equal-weight average of Nb_Avg successive spectra. After the Nb_Avg spectra have been observed the result is frozen.

 

In both cases the Reset button discards the present display and restarts the averaging from zero.

 

The Averaging Mode can be chosen from several choices:

• No Averaging Only presents instantaneous power spectra, irrespective of the other settings.

• Vector Averaging Vector averaging eliminates noise from synchronous signals. Vector averaging computes the average of complex quantities directly. The real part is averaged separately from the imaginary part. Averaging the real part separately from the imaginary part can reduce the noise floor for random signals because random signals are not phase coherent from one time record to the next. The real and imaginary parts are averaged separately, reducing noise but usually requiring a trigger.

• RMS Averaging RMS averaging reduces signal fluctuations but not the noise floor. The noise floor is not reduced because RMS averaging averages the power of the signal. RMS Averaging is the most common type.

• Peak-Hold Peak hold averaging retains the peak levels of the measured spectra. Peak hold averaging is performed at each frequency line separately, retaining peak levels from one FFT record to the next.

 

Note: All the FFT calculation is performed on the PC. The raw time-signals are transferred from the instrument to the PC, where the FFT and averaging calculations are performed.