Time Domain Reflectometer

A time-domain reflectometer (TDR) is an electronic instrument that uses time-domain reflectometry to characterize and locate faults in metallic cables. It can also be used to locate discontinuities in a connector, printed circuit board, or any other electrical path.

A TDR measures reflections along a conductor. In order to measure those reflections, the TDR will transmit an incident signal onto the conductor and listen for its reflections. If the conductor is of a uniform impedance and is properly terminated, then there will be no reflections and the remaining incident signal will be absorbed at the far-end by the termination. Instead, if there are impedance variations, then some of the incident signal will be reflected back to the source. A TDR is similar in principle to radar.

Radio Communications Cable

example test products for radio cable

Kit: An inexpensive Fast Clock Time Domain Reflectometer kit is available which can be used with a medium speed (50 MHz typically) or faster Oscilloscope. This device will determine key parameters about cable lengths, position of cable faults and assist in cable characterization. In use the TDR clock signal is 'stretched' out on the oscilloscope to display the square wave 'ringing', once achieved the test cable can be attached and the un-terminated return pulse will cause a second 'bump' in the square wave to be seen on the display (see photos in listing). Using simple math and the return path speed measured from the scope display, cable length can be determined.

AEA 2020 TDR RF Coax & Cable Step Time Domain Reflectometer Cable Fault Analyzer: instrument. uses the TDR step pulse for better accuracy in finding cable faults.