Site Master™ S331L User Guide : Cable and Antenna Measurements : Trace
 
Trace
The Site Master S331L 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 using trace math functions. Pressing the Trace (5) main menu key will bring up the trace functions.
Overview of traces:
• Recalled measurements (.dat files) from internal memory or a USB stick are automatically copied to trace memory and displayed.
Note 
Recalled measurements may change the current instrument settings.
• Copy Trace to Memory 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 (Trace Display) also include viewing only the trace in memory or both traces.
• View only trace memory to have marker values apply to the purple trace.
Displaying a Live Trace and a Static Trace from Trace Memory
From the Trace menu, users can Copy Trace to Display Memory. The copied trace can be displayed on the Site Master and used for trace math. Trace Display allows viewing of two traces at the same time to compare the trace stored in memory to the live trace. Trace Math operations include Trace – Memory, Trace + Memory and (Trc + 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 cables.
1. Connect the first cable and setup the measurement. Refer to Measurement Setup for additional information.
1. Press Trace (5) and then Copy Trace To Memory.
2. Remove the first cable and connect the second cable.
3. Press Trace Display and select Trace & Memory. The purple trace from trace memory is displayed along with the live (yellow) trace.
Trace Overlay of Two Cables
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. Complete the steps described in Trace Overlay.
2. Press Trace Math and select Trace - Mem , Trace + Mem, or
(Trc + Mem) / 2 (Figure: Trace Memory Used to Compare the Phase of Two Cables).
Trace Memory Used to Compare the Phase of Two Cables
 
Notes
The trace math functions often seem backwards to new users. The points to remember with Trace - Memory,
Trace + Memory, and (Trc + 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 (1 of 2)
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 (Trc + 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.