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Operating Concepts
Noise Reduction Techniques
Noise Reduction Techniques
The key is used to access three different noise reduction techniques: sweep-to-sweep
averaging, display smoothing, and variable IF bandwidth. All of these can be used
simultaneously. Averaging and smoothing can be set independently for each channel, and
the IF bandwidth can be set independently if the stimulus is uncoupled.
Averaging
Averaging computes each data point based on an exponential average of consecutive
sweeps weighted by a user-specified averaging factor. Each new sweep is averaged into the
trace until the total number of sweeps is equal to the averaging factor, for a fully averaged
trace. Each point on the trace is the vector sum of the current trace data and the data from
the previous sweep. A high averaging factor gives the best signal-to-noise ratio, but slows
the trace update time. Doubling the averaging factor reduces the noise by 3 dB. Averaging
is used for ratioed measurements: if it is attempted for a single-input measurement (e.g. A
or B), the message CAUTION: AVERAGING INVALID ON NON-RATIO MEASURE is displayed.
The effect of averaging on a log magnitude format trace is shown in Figure 7-18.
NOTE If you switch power ranges with averaging on, the average will restart.
Figure 7-18 Effect of Averaging on a Trace
Avg
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