As the frequency of a signal traveling over a wire conductor increases, the signal moves further away from the center of the conductor and travels mostly on the outer surface of the wire.

This can cause a lot of confusion when working with very high frequency devices. If you take a measurement with an ohmmeter, it reads like a good solid wire. If you send the signal down the wire, it acts like the wire is broken. If the surface of the conductor is nicked, it can act as an open, reflecting the signal back to the source. When working with high frequency devices and antennas, use non-metallic wire strippers or heat strippers. They can save you a lot of grief.