Appreciation post: The old phone line trick for finding a break in coax

I was helping a friend rewire his house in Tacoma last month and hit a wall. We had a coax run that tested fine for continuity but the signal was garbage. I was about to start cutting open walls when I remembered something my first trainer said years ago, something I thought was just an old wives' tale. He said you can use a basic analog phone with a toner to find a break in shielded cable, not just phone lines. I dug out my old butt-in set, hooked the toner to the coax center conductor, and used the inductive probe on the outside of the cable. Sure enough, about fifteen feet into the attic, the tone dropped out. The outer shield was damaged but the center conductor was still connected, which is why my continuity tester lied. Found a mouse had chewed it. Saved us hours of work. Has anyone else had luck with that method, or is there a better tool for that specific kind of fault?

3 comments

3 Comments

matthew_west10h ago

So you just toned the shield and not the center conductor?

the_hayden8h ago

Honestly that method sounds like a total hack, why not just use a proper TDR? The old phone toner trick is way too hit or miss for professional work, you can get false readings all the time. It's a cool story but not a reliable fix.

mason2731h ago

Hit or miss" maybe, but it got the job done when the TDR was back at the shop. Sometimes you just need to know if the shield is continuous, not the exact distance to a fault. For a quick field check, it's plenty reliable.