Method and apparatus for measuring the bit error frequency in a cable caused by crosstalk between line pairs during transmission of a 3-level coded PCM signal

Apparatus for measuring in a multipair cable the bit error frequency caused by crosstalk from one disturbing pair on which are transmitted pulse signals to a given length of a disturbed pair intended for transmission of a 3-level coded PCM signal, comprising:

• a manually adjustable equalizer having an input connected to the disturbed pair;
• two level detecting circuits, each of said level detecting circuits having a disturbance signal input connected to the output of said equalizer, each of said circuits having a sampling input and means in response to a signal at the sampling input for emitting a signal of a given level only when the amplitude of the signal at its disturbing signal input exceeds a given amplitude, one of said circuits being only operative for positive polarity signals, the other of said circuits being operative for only negative polarity signals;
• a free-running clock generator means having an output connected to the sampling input of each level detecting circuit for synchronous sampling;
• and an error counting means having an input connected to the output of each level detecting circuit for registering the number of instances that the magnitude of the equalized disturbances exceed the threshold level of the level detecting circuits whereby the corresponding error frequency which the intended PCM signal would show when transmitted via the cable length corresponding to the equalization length is proportional to to the number of registrations and inversely proportional to the time required to obtain said number of registrations.