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I'm in the process of setting up a DSL modem/wifi router, which should be connected to a phone line that uses a single twisted pair. However, the phone line enters my house in a slightly inconvenient location. I could run a phone cable to a better location, but my house already has coaxial cables running through it, that I'm not using otherwise.

Can I connect the phone line to the coaxial cable, and plug in my modem at the other end? They're both pairs of copper wires; or is there a reason this shouldn't work?

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    \$\begingroup\$ What kind of coax? What country are you in (local regulations may frown on doing this)? Physically it would probably work but there would likely be an impedance mismatch at the joint between the UTP and the coax which would possibly degrade the DSL performance. If I were you I'd just use one of the coax lines as a pull-through for a new UTP line. \$\endgroup\$ – Wossname May 29 at 10:32
  • \$\begingroup\$ It sounds like it would be fairly easy/cheap to try it. If the data rate suffers then you know the answer! \$\endgroup\$ – hekete May 29 at 12:53
  • \$\begingroup\$ No, there isn't a way to impedance match the two, and coaxial is not differential \$\endgroup\$ – Voltage Spike May 29 at 19:39
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Can I connect the phone line to the coaxial cable, and plug in my modem at the other end?

The conservative answer has to be "no" - phone lines are "balanced" in that the impedance presented by each wire to ground is constant. Coax cable is "unbalanced" and the impedance presented by the screen can be vastly different to the impedance presented to ground by the inner core.

The telephone cable's natural characteristic impedance is around 600 ohm whereas the coax cable might be 50 ohms or 75 ohms and it could cause data symbol reflections and therefore an excessive bit error rate when attached to a system expecting 600 ohm.

However, being less conservative, if the coax cable is short (say no more than a few metres) then you might get away with it being inserted.

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