Ever since I moved into my house the upstairs cable has not worked, so I recently I started looking into fixing the cable wiring and figuring out how its laid out in the house.

I bought a Southwire M550 to trace the coax cables run under the house and attic, and discovered a strange issue. One of the coax cables, when tested using the M550, shows that there is a miswiring and a reversal issue. I thought these types of issues were more reserved for network cable, where there are individual pairs within the cable, but a reversal within a coax? Would this be an issue with a splitter where it has in/out sides, and maybe the hookup is reversed?

1 Answer 1


From what I can determine from the instruction manual for the tester, and my previous experience as a cable television technician, the test requires a free-floating cable in order to be tested properly. Your question regarding a splitter is valid, as there are electronic components within a splitter that will generate failed tests. "In the old days," one attached a 75 ohm terminating resistor to a piece of coax being tested and read the opposite end using an ordinary volt-ohm meter. If the reading was approximately 75 ohms, the correct cable was identified and was possibly healthy.

If the cable was already confirmed as correct and the reading appeared shorted, it was likely there was either damage or an in-line splitter, typically buried in an attic or nearly unreachable in a crawl space!

You can confirm the reading you see if you have a splitter in hand, along with a known-good segment of coax. Connect only the coax, test it (as good, of course), then attach the splitter and observe the difference.

  • Thank you for your reply. I plan to get back around to investigating this issue shortly, and will report back.
    – Jeffrey
    Commented Dec 28, 2017 at 4:01

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