Near-end communications line characteristic measuring system with a voltage sensitive non-linear device disposed at the far end

A method for measuring the characteristics of a communications line having a near end and a far end and being capable of transmitting communication signals between said near end and said far end at normal voltage levels, said method comprising the steps of:

• terminating said far end of said communications line with a voltage sensitive non-linear means having a linear region and a non-linear region, said voltage sensitive non-linear means;
• exciting said voltage sensitive non-linear means with an excitation signal of sufficient amplitude to drive said voltage sensitive non-linear means into its non-linear region, said excitation signal having a voltage level larger than said normal voltage levels used to transmit said communication signals through said communications line;
• providing at least one low level test signal to said communications line at an associated measurement frequency during a time when said voltage sensitive non-linear means is in its non-linear region, said test signal not contributing significantly to the non-linearity of said voltage sensitive non-linear means;
• said provided at least one test signal being harmonically mixed with said excitation signal and causing a new frequency to be generated at said far end of said communications line while said voltage sensitive non-linear means is in its non-linear region, said generated new frequency comprising a measurement signal, said measurement signal traveling from said far end to said near end of said communications line;
• and
• frequency selective measuring said measurement signal provided to said near end and comparing a known calibration signal against said generated new frequency for determining said characteristics of said communications line based thereon.

A system for detecting the presence of a non-linear device on a communications line, said communications line having a near end and a far end and being capable of transmitting signals between said near end and said far end, said system comprising:

• voltage sensitive non-linear means connected to said communications line and disposed at said far end of said communications line, said voltage sensitive non-linear means having a linear region and a non-linear region;
• excitation signal generation means connected to said communications line for providing an excitation signal of sufficient amplitude to said voltage sensitive non-linear means for driving said voltage sensitive non-linear means into its non-linear region;
• test signal generation means connected to said communications line and disposed at said near end of said communications line for providing at least one test signal to said communications line;
• said test signal not contributing significantly to the non-linearity of said voltage sensitive non-linear means, said non-linearity of said voltage sensitive non-linear means appearing at said communications line far end as a result of harmonic mixing of said excitation signal and said test signal causing a new frequency to be generated at said far end of said communications line as a result of said provided at least one test signal, said generated new frequency traveling from said far end to said near end of said communications line for providing a detection signal to said near end from said far end;
• and
• detection means at said near end for detecting said detection signal provided to said near end from said far end.