Time Domain Reflectometer (TDR)

Posted on Feb 5, 2014

This Time Domain Reflectometer (TDR) based on circuit idea published in Electronics Design October 1, 1998 magazine. Time Domain Reflectometer modified version by Tomi Engdahl which you see in this document. The circuit has been tested with wide variety of cables. This reflectometer circuit is best powered with 4. 5V battery or three 1. 5V AA batter

Time Domain Reflectometer (TDR)
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ies connected in series. The + from battery goes to IC1 pin 14. The pin 7 of IC1 is connected to circuit ground which is connected to circuit ground. Remember to put a 100 nF (ceramic or polypropylene) capacitor between IC1 pins 7 and 14 to guarantee stable operating voltage for the circuit. TDRs are used in all phases of a cabling system`s life, from construction to maintenance and to fault finding. Historically, the TDR has been reserved for only large companies and high level engineers. This was due to the complexity of operation and high cost of the instruments. If a cable is metal and it has at least two conductors, it can be tested by a TDR. TDRs will troubleshoot and measure all types of twisted pair and coaxial cables. TDRs can locate major or minor cabling problems including; sheath faults, broken conductors, water damage, loose connectors, crimps, cuts, smashed cables, shorted conductors, system components, and a variety of other fault conditions. TDR can be used to locate the problem type and in which place along the calbe the fault is. The TDR works on the same principle as radar. When that pulse reaches the end of the cable, or a fault along the cable, part or all of the pulse energy is reflected back to the instrument. Any impedance change in cable will cause some energy to reflect back toward the TDR and will be displayed. How much the impedance changes determines the amplitude of the reflection. The TDR...

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