Cable and Antenna Analyzer Measurement Guide : Cable and Antenna Analyzer Measurements : Setting Trace Parameters
 
Setting Trace Parameters
The Cable and Antenna Analyzer allows the user to concurrently view the live trace and a second trace that is stored in trace memory. The user can compare the two traces visually or by using trace math functions. Selecting TRACE on the main menu will bring up the trace menu.
Overview of traces:
• Recalled measurements (.fmcaausb/.smcaa 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).
Displaying a Live Trace and a Static Trace from Trace Memory
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. Refer to Setting up a Measurement for additional information.
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 Amplitude) have not changed since the trace was copied to memory.
If one of the traces is cut off, pressing AMPLITUDE > 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. Refer to Setting up a Measurement for additional information.
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, Trace + Mem, or (Trace + Mem) / 2 (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, and (Trace + Mem) / 2 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).
(Trace + Memory) / 2
(not shown)
In the (Trace + Memory) / 2 graph, the yellow trace is the result of adding the purple trace to the active trace and then dividing the result by 2.
This math function is most useful when measuring one-port Cable Loss (using the Cable Loss measurement).
1. Connect a Short to the end of the cable and store the trace into memory.
2. Next, connect an Open to the end of the cable and apply (Trace + Mem) / 2 math function.
Because the ripple generated by the Short and Open are 180° out of phase, the effect of this math function will be to cancel out the ripple, resulting in a more accurate cable loss measurement.
Refer to TRACE Menu for additional information.
 
TRACE 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 difference between the active trace and the trace in memory.
• Trace – Mem: Displays the results of logarithmic adding of the active trace and the trace in memory.
• (Trace + Mem) / 2: Displays the results of the average of the active trace and trace in memory.