A Traditional TDR Cable Tester With <2cm Resolution

What can you see, test and measure with a traditional time domain reflectometer (TDR)? The answer is “more than you might expect”:

  • measure impedance variations in connectors/filters/antennas/PCBs
  • locate short/open circuits and damage in cables
  • locate intermittent faults in cables and connectors
  • locate connectors in cables

and can resolve discontinuities around 2cm apart. That resolution is at least 10 times better than can be obtained with the typical homebrew logic pulse + oscilloscope combination.

I recently bought a couple of cheap 1970s Tektronix 1502s in the hope that I could make a single working frankenmachine.  My initial assessment was depressing: one had a cracked and broken case (so I assumed the CRT was also broken), the other’s electrolytic caps had spewed acid across the PSU and had a faulty 2kV PSU, and both had defective NiCd batteries – and it won’t even start without a working battery. But eventually I managed to get both working: I recapped the PSUs, rewelded the case with methylene chloride, used my “new” 12kV scope probe and 40kV meter to repair the HV PSU, created a “NiCd emulator”, and the CRT wasn’t damaged after all. Later reading of a TekScope magazine indicates it isn’t surprising the CRT survived: it is mechanically completely isolated from the chassis to protect against up to 26 12″ drops.

So I am now the proud possessor of two nice little portable waterproof instruments, literally designed for field use – one of the service manuals indicates they were used with Patriot missile defence systems.

Tektronix 1502 TDR Cable Tester

Tektronix 1502 TDR Cable Tester

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