This simple circuit allows you to use your oscilloscope as a Time Domain Reflectometer (TDR). This is how it works. Send a pulse down a cable and watch for the reflection. Most people think a TDR is more complicated than this. Your oscilloscope is used to sample and view the reflected waveform. In this circuit we use the 74HC4040 counter to create the length of the pulse we will send down the cable. Build this inexpensive circuit and now you will have a TDR.
Via Electronics Lab.