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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) and the relative significance is shown in the
Data-Mem values.
Data Analysis Features
memory.
Data
Math.
[D+M] Current trace data added to memory data.
Data + Memory
o
Data – Memory
[D-M] Current trace data subtracted from memory data.
o
[D/M] Current trace data divided by memory data.
Data / Memory
o
[Data] Displays trace data with NO math applied.
Math Off
o
Values to compare
0.5 dB and 0.6 dB
0.5 dB and 0.7 dB
Values to compare
–10 dB and –12 dB
–50 dB and –52 dB
to store the current data trace into
Data->Mem
Data/Mem
0.1 dB
0.2 dB
Data/Mem
2 dB
2 dB
Data-Mem
–39 dB
–33 dB
Data-Mem
–24 dB
–64 dB
85
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