Selecting an Averaging Type

Several types of averaging functions are available but not all average types are available for all measurement hardware.

If the hardware does not support a particular average type, that average type is greyed in the menu and cannot be selected.

Selecting an average type that the current demodulator does not support will cause the Averaging Type to default to Off.

For both RMS and Time averaging, the VSA provides linear or exponential averaging. Linear averaging gives uniform weight to all data used in the average. Time Exponential averaging weights new data more than old data, which is useful for tracking data that change over time.

By default, Time Exponential averaging continues indefinitely. This differs from the default for linear averaging, which stops when the VSA reaches the number of averages specified. However, the VSA can be configured to perform consecutive linear averages by selecting the Repeat Average check box.

Available Average Types:

Exponential Averaging

Some of the averaging types provided by the VSA use exponential averaging. Unlike linear averaging (also called non-exponential or normal averaging), exponential averaging weights new data more than old data. This is useful for tracking data that changes over time.

With exponential averaging, the number of averages selected determines the weighting of old versus new data. As the number of averages increases, new data is weighted less.

With exponential averaging, it's especially important to set the number of averages carefully. If there are too few averages in the measurement, the averaging does not smooth out variances. But if there are too many averages, the VSA may not track subtle changes occurring within the data.

To calculate the exponential average, the VSA uses this formula:

$image\exp-avgFormula_wmf.jpg$

where N is a weighting factor (the number of averages specified).

When an exponential average is started, N equals 1 for the first average, 2 for the second average, and so on, until N equals the number of averages specified. This reduces the variance quickly during the startup of an exponential average.

Above the trace, an annotation displays "AVG: N" (where AVG indicates the average type, and N shows the current average.) For exponential averages, when N equals the number of averages specified, the VSA no longer increments N, even though it continues to collect averages.

Until the measurement reaches the specified number of averages, there is no difference between rms (video) exponential averaging and rms (video) averaging.

By default, exponential averages continue indefinitely. This is different than the default for non-exponential averages, which stop when the VSA reaches the number of averages specified. However, the VSA can be configured to stop during an exponential average using single sweep or an exponential average can be paused using Pause/Single.