Vector Network Analyzer (VNA) Measurement Guide : VNA Calibration and Measurements : Setting Trace Parameters
 
Setting Trace Parameters
A trace is a measurement result that can have user-defined attributes assigned to it for display purposes. You can assign the following attributes for a trace: S-parameter, Graph Type, Domain, and Smoothing. Using the Scale menu, you can independently set the scale for each trace.
Overview of traces:
• Recalled measurements (.smvna files) are automatically copied to trace memory and displayed.
Note 
Recalled measurements may change the current instrument settings.
• COPY TO MEM will replace whatever is in memory with the live (yellow) trace. The memory trace (purple) is displayed behind the live (yellow) trace.
• The default view is live Trace only. View options (MEMORY DISPLAY) include viewing only the trace in memory or both traces.
• Active markers can be applied to the purple trace memory by pressing MARKER > TO MEMORY (refer to Setting Up Markers).
Smith Chart and Log Magnitude Display - Trace Menu
MEMORY DISPLAY allows viewing of two traces to compare the trace stored in memory to the live trace. Trace MATH operations include Trace – Memory, Trace + Memory and (Trace + Memory) / 2. Saved traces can also be recalled and compared with the live trace.
Trace Overlay
The examples below illustrate how the trace overlay feature can be used to compare the return loss measurements between two antennas.
1. Connect the first antenna and set up the measurement. .
2. Select TRACE > COPY TO MEM.
3. Remove the first antenna and connect the second antenna.
4. Select MEMORY DISPLAY and select Both. The purple trace from trace memory is displayed along with the live (yellow) trace.
Trace Overlay of Two Antennas
Note 
The trace from memory can only be displayed if the measurement settings (except for SCALE) have not changed since the trace was copied to memory.
If one of the traces is cut off, pressing SCALE > FULLSCALE will adjust the reference level to display both traces.
Trace Math Example
The example below illustrates how the trace math features can be used to compare the phase of two cables.
1. Connect the first cable and set up the measurement.
2. Select TRACE > COPY TO MEM.
3. Remove the first cable and connect the second cable.
1. Select MEMORY DISPLAY and select Both. The purple trace from trace memory is displayed along with the live (yellow) trace.
2. Select MATH and select Trace - Mem or Trace + Mem (Figure: Trace Memory Used to Compare the Phase of Two Cables (see Table: Trace Math Details)).
Trace Memory Used to Compare the Phase of Two Cables (see Table: Trace Math Details)
Note 
The trace math functions often seem backwards to new users. The points to remember with
Trace – Mem, Trace + Mem, are:
The numbers on the y-axis are negative.
The purple trace is added to or subtracted from the live trace. The sum or difference of the live trace and memory trace is displayed in yellow.
 
Trace Math Details 
Example Description
A. Sample Traces
Shows the live yellow trace and purple memory trace.
B. Trace – Memory
In the Trace - Memory graph, the yellow trace is the result of subtracting the purple trace from the active trace (not displayed in Example B,
Trace - Memory, but shown in Example A).
Note that the yellow Trace - Memory is at 0 or above (and off the graticule) whenever the yellow trace is above (has a greater value than) the purple trace (refer to A).
The two down sloping bumps in Example B are when the purple trace moves above the yellow trace. In Trace - Memory, this results in a negative value that is displayed.
C. Trace + Memory
In the Trace + Memory graph, the yellow trace is the result of adding the purple trace to the active trace (not displayed in Example C,
Trace + Memory, but shown in Example A).
Note that the yellow Trace + Memory is below 60 (and off the graticule) whenever adding the yellow trace value to the purple trace value is greater than 60 (refer to A).
D. Multiply
E. Divide
F. Average
Refer to TRACE Menu for additional information.
TRACE Menu
Access TRACE menu from main menu.
TRACE Menu
 
COPY TO MEM
Copies the currently active trace to memory for use in the display and math and options below.
MEMORY DISPLAY
Selects the trace display options.
• Trace: The active trace is shown in yellow.
• Memory: The trace stored in memory is displayed in purple.
• Both: Displays both the stored trace (purple) if a trace is stored in memory and the current active trace (yellow).
MATH
Select to change the trace math options.
• None: The active trace is shown as is with no math functions.
• Trace + Mem: Displays the results of logarithmic adding of the active trace and the trace in memory.
• Trace – Mem: Displays the difference between the active trace and the trace in memory.
• Multiply: Displays the results of logarithmic product of the active trace and the trace in memory.
• Divide: Displays the results of logarithmic ratio of the active trace and the trace in memory.
• Average: Displays the results of logarithmic average of the active trace and the trace in memory.
SMOOTHING
Sets the smoothing aperture value for specified trace. The range is from 0% to 20%.