Hi I am using the 80E08 TDR heads to get the differential S-parameters from my active device. I am just trying to get SD1D1 and SC1C1 So calculate the S11, Iconnect requires the reference and the DUT. My question is specific on the reference. It could be an step coming an open or a short. When I drive the diff. pair in odd mode. The reference step for an open is just the inverse for a short. i.e. Shorting Dp to Dn. (not to GND) When I drive the diff. pair in even mode. The reference step for an open seems to be the same as for a short. i.e. Shorting Dp to Dn. (not to GND). So , the question is, for the case of a SHORT in both the ODD and EVEN modes, should I short the end of the trace to GND or the short is between the Dp and Dn Thanks Juan ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu