Trace averaging vs video filtering
To reduce the effect of noise on the trace and, as a consequence to smooth the trace, traditional analog swept-tuned spectrum analyzers include a variable video filter. Instead to reach this goal, modern instruments offer also the possibility to average the trace over a number of sweeps.
Video filter is a low-pass filter with a variable cut-off frequency. The narrower the video filter bandwidth, the higher the smoothing degree, the longer the sweep time.
Instead, trace averaging has not effect on sweep time but to obtain the same degree of smoothing reached with video filtering we need more or less the same time because of the number
of sweeps required.
But when we want to analyze signals with a spectrum that changes with time, we can get different results from the two above-mentioned methods.
This is what the video shows.
The input signal performs a frequency hop during the analysis.
When the video filter is used in order to smooth the signal, the output does not show any frequency component of the input signal.
Instead when the trace averaging is applied, it is possible to identify the frequency components of the input signal.