Performance Spectrum Analyzer Series Optimizing Dynamic Range for Distortion Measurements
●Introduction
■Its wide dynamic range makes the spectrum analyzer the test instrument of choice for measuring harmonic distortion, intermodulation distortion, adjacent channel power ratio, spurious-free dynamic range, gain compression, etc. Distortion measurements such as these are bounded on one side by the noise floor of the spectrum analyzer and on the other side by the signal power strength at which the spectrum analyzer’s internally generated distortion masks the distortion being measured. The simultaneous low noise floor and low internally generated distortion products uniquely qualify the spectrum analyzer for making distortion measurements.
■Having wide dynamic range and accessing this dynamic range are two different things. Unless the user is given enough information on how to optimize the spectrum analyzer to make distortion measurements, its dynamic range performance cannot fully be exploited. Many distortion measurements are very straightforward: measure the fundamental tone power, measure the distortion product power, and compute the difference. Problems arise when the device under test has distortion product levels that approach the internally generated distortion product levels of the spectrum analyzer. Further complications arise when trying to maximize speed and minimize measurement uncertainty. In these cases more care in the measurement technique is require.
■The search for information on making distortion measurements begins with the spectrum analyzer data sheet. The data sheet is most useful for comparing one spectrum analyzer against another in its dynamic range capability and the relevant measurement uncertainties in the distortion measurement. What the data sheet fails to convey is how to configure the spectrum analyzer to achieve the specified dynamic range performance.
■Primers are another source of information. Two excellent references are [1] and [2] listed on page 39 of this document. Primers such as these provide the necessary fundamental knowledge for making distortion measurements. Yet, primers treat spectrum analyzers as a general class of test instrumentation. In order to make truly demanding distortion measurements accurately or less demanding measurements more quickly, the user needs product specific information.
■This product note bridges the gap between primers and data sheets, focusing on distortion measurements using the Keysight Technologies, Inc. performance spectrum analyzer (PSA) series (model E4440A). Part I is a self-contained section for making the less demanding distortion measurement quickly using the auto-coupled settings found in the PSA. Part II guides the user in setting the appropriate power at the input mixer in order to maximize the dynamic range for carrier wave or continuous wave (CW) measurements. Part III explains the measurement of distortion measurements on digitally modulated signals. Part IV details some of the internal architecture of the PSA as it relates to distortion measurements. Finally, Part V describes some measurement techniques, both internal and external to the PSA, that yield more accuracy in certain kinds of distortion measurements.
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Application note & Design Guide |
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Please see the document for details |
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English Chinese Chinese and English Japanese |
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March 12, 2018 |
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5980-3079EN |
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2.7 MB |
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