About Math Operations - Keysight N9912A User Manual

Data Analysis Features
All about Trace Math

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.
Values to compare
0.5 dB and 0.6 dB
0.5 dB and 0.7 dB
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
–10 dB and –12 dB
–50 dB and –52 dB
16- 20
— 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.
Data/Mem
0.1 dB
0.2 dB
Data/Mem
2 dB
2 dB
Data-Mem
–39 dB
–33 dB
Data-Mem for Data-Mem for
S-parameters absolute power
with 20*log levels with
relationship 10*log
relationship
–24 dB -14dB
–64 dB -54dB
Keysight N9912-90001 User's Guide