3M
™
 Advanced Systems Tester 900AST Series
39
Single Trace
Insert the supplied coaxial TDR test lead into the 
Red and Black test jacks on the 900AST tester. 
Connect one TDR test lead to a single conductor 
or one side of a pair under test. Test lead polarity 
is not important for TDR measurements. If a single 
conductor circuit is being tested, connect the other 
TDR test lead to another de-energized conductor 
near the conductor under test. TDR pulses occur at 
such a high frequency that an adjacent conductor 
can serve effectively as a ‘return’ for the pulse. 
Ground or cable shield can also be used for the 
return if desired, but this often results in a very 
“noisy” trace and is not recommended. If a pair of 
conductors is being tested, place the other test lead 
on the second conductor of the pair. Single Trace is 
used to view events on a single circuit at a time.