Agilent Technologies FieldFox N9923A User Manual page 50

When the Alias-free Range = Off, the following procedure will help to determine
if a response is true or an alias response:
1. Put a marker on the response in question and note the distance to the fault.
2. Change the start or stop distance.
A true fault response will not move in distance. That is, if a true fault is present
at 10.3 meters, changing the stop distance from 15 m to 20 m will not move the
fault; the fault will remain at 10.3 meters. However, an alias response will
appear to move.
An un-terminated cable (with NO perfect load at the end) will show faults that
appear to be beyond the end of the cable. These are NOT alias faults. These faults
appear as the signal reflects off the open at the end of the cable and travels back
down the cable toward the connection at the FieldFox. Re-reflections are
measured at the FieldFox as mirror images of the original faults. The largest fault
is the open end of the cable. To avoid confusion, set the Stop distance shortly
after that fault.
50 N9923A FieldFox User's Guide