You can edit a data register to do the following:
• Modify a trace to remove an objectionable component. For example, you can “zero
out” part of a trace by defining a line segment from point to point. You can do this
for any type of trace.
• Modify a waveform to use as an arbitrary source. For example, you can remove the
lower half of a sine wave (in the time-domain) by drawing a line segment between
the negative crossover points of the sine wave.
• Specify a weighting function for a curve fit operation. See “To specify a weighting
function,” in chapter 16, “Curve Fit.”
• Specify a weighting filter for a trace. The analyzer has three filters, A-weight,
B-weight and C-weight that are available as math operations. You can modify one
of these filters to create your own filter.
Using Logarithmic Values with Math Operations
The analyzer performs math operations in linear
units, not logarithmic units. This is true
regardless of the trace coordinate.
All math operations occur before the analyzer
converts measurement data to the display units.
This is important to keep in mind when you need
to add (or subtract) units with logarithmic
values—for example, if you need to compensate
for a gain or loss in your measurement system.
Suppose you want to add 3 dB to your
measurement results. You can not build a math
function that simply adds 3 dB since math
operation are done with linear units. Instead, you
must take a trace and multiply it by the antilog of
the offset (in dB) that you want. This converts
the 3 dB to linear units—and you can express
this offset as 10 to the x/20, where x is the dB
offset. To convert power spectra units, you
express the offset as 10 to the x/10, where x is
the dB offset.
So, if you want to add 3 dB in linear units, you
must multiply a trace by 1.414. If you want to
subtract 3 dB in linear units, you can divide the
trace by 1.414 (or conversely, you can multiply
the trace by 0.707). If you want to add 3 dB in
power spectra units, you must multiply by 1.995.
If you want to subtract 3 dB in power spectra
units, you must divide by 1.995.
Agilent 35670A
Operator's Guide Math Operations and Data Editing
18-3
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