There was an excellent article way back in 1988 on Differential TDR Testing Techniques in Connection Technology March 1988. If you have trouble finding it give me a call at 714-951-3388 and I will fax you a copy Regards, Alan Cochrane Multek ______________________________ Reply Separator _________________________________ Subject: FAB: ODD-EVEN Mode Impedance Author: [log in to unmask] at INTERNET_GATEWAY Date: 5/22/96 4:44 PM Could anybody please explain the "odd mode" the "even mode"and the "common mode" impedance's, as in Differential Impedance. What they are, the benefits and drawbacks? Thanks,