On Fri, 11 Sep 2009 11:32:48 -0400, "solarwind" said: > On Fri, Sep 11, 2009 at 6:28 AM, peter green > wrote: > > It is generally a twisted pair but typically not a particulally tightly > > twisted one. Some older phone wiring and a lot of cheap extentions are > > not twisted > > I thought that in a twisted pair line, the pair would carry the signal > and a third wire is required for ground. How does twisted pair > signalling work with only two wires? As in any wired circuit, current goes out one wire and returns in another. In the twisted pair it is just the same. Ground is not needed. There are usually limitations about how far the voltage can be from ground, but the circuit itself is made by the two wires in the pair. Cheers, Bob -- http://www.fastmail.fm - Or how I learned to stop worrying and love email again -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist