Use a TDR, time-domain reflectometer. There are very expensive, fancy
ones, but you can build a simple one easily if you have a scope. This
sends a pulse down the line which bounces off the open. Knowing the
round-trip time and the Vf of the cable, you can calculate the
distance to the break.
Another option is to use a noise bridge or SWR analyzer. Find the
lowest frequency at which the impedance goes to minimum. The length
of cable to the break is 1/4 wave at this frequency. Again using
Vf and freqeuncy you can figure length to the break.
-Tony, K1KP, email@example.com
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