By Steve Murray, Keithley Instruments, Inc.
Averaging is a common technique for reducing the measurement uncertainty inherent in all measurements. Performing the same measurement a number of times and calculating the average of the measured values can often reduce the randomness of an experimental result. Many (if not most) instruments attempt to simplify the measurement process by performing averaging automatically. Rather than returning 100 noisy measurements, the instrument is responsible for taking all 100 measurements, calculating their average, and returning just the average. Averaging is so common and conceptually simple that one might assume there's little room for debate on the correct way to average. However, recent experience has demonstrated that power averaging in spectrum analyzers isn't necessarily straightforward. The following discussion explores the issues associated with power averaging in order to help readers avoid making the same mistaken assumptions the author did. The conclusions presented here are the results of an experiment that involved correlating the power measurements of two spectrum analyzers from different vendors. However, the issues discussed are generic in the sense that they apply to any spectrum analyzer power measurement with some form of post-detection averaging.
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