Keysight N9913B, Руководство пользователя

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Data Analysis Features
All about Trace Math
Keysight N9938-90006 User’s Guide 751
— Data – Mem D-M] Current measurement data is subtracted from the data in memory.
— Data / Mem [D/M] Current measurement data is divided by the data in memory.
— Math Off [Data] Displays trace data with NO math applied.
About Math Operations
Data / Memory and Data - Memory math operations are performed on complex linear data before it
is formatted. Because data is often viewed in log format, it is not always clear which of the two
math operations should be used. Remember: dividing linear data is the same as subtracting
logarithmic data. The following illustrates, in general, when to use each operation.
Use
Data / Memory for normalization purposes, such as when comparing traces “before” and
“after” a change is made or when measuring trace noise. In the following table, the Data/Mem
values intuitively show the differences between traces. It is not obvious what Data-Mem is
displaying.
Use Data - Memory to show the relative differences between two signals. Use for comparison of
very small signals, such as the S11 match of two connectors.
In the following table, Data/Mem shows both pairs of connectors to have the same 2 dB difference.
However, the second pair of connectors have much better S11 performance (–50 and –52). The
relative significance is shown in Data-Mem .
Values to compare Data/Mem Data-Mem
0.5 dB and 0.6 dB 0.1 dB –39 dB
0.5 dB and 0.7 dB 0.2 dB –33 dB
Values to compare Data/Mem Data-Mem
–10 dB and –12 dB 2 dB –24 dB
–50 dB and –52 dB 2 dB –64 dB