About TDR, The good news is that the error is supposed to get worse the further you are from 50 ohms impedance. I won't claim to know too much about this since I'm a Materials Engineer, not an EE. The guy to talk to is Mike Trangmontage (spelling?) at Tektronics. He's the TDR guru who happens to sell a PC based program to measure TDR. He has a good paper on it to. I haven't spoken to him in about 3 years but I have his number as 617-861-5846 or 1-800-756-7000 box #863-6001. Yes you can calibrate the unit for whatever value but usually it gets calibrated to 50 ohms. If you usually measure impedances of 100 ohms, then you might want to calibrate it with a standard of 100 ohms. We use a 50 ohm airline standard that doesn't need to be certified yearly. However, when I was looking about 4 years ago, no one was making 100 ohm airlines. Check with Mike on using resistors. I think its ok to use if I remember. I assume you already have the IPC test method on performing TDR. There's some useful info in it. Regards, Paul Terranova Analytical and Environmental Test Services Lab Digital Equipment Corporation 200 Forest Street Mail Stop: MRO3-1/D2 Marlboro, MA 01752-3085 ' Phone: (508)467-3109 * Fax: (508)467-6796 * Email: [log in to unmask] WebSite: http://www.digital.com/lab-services -----Original Message----- From: Glynn Shaw [mailto:[log in to unmask]] Sent: Wednesday, May 06, 1998 12:27 PM To: [log in to unmask] Subject: [TN] Quick Check of TDR Impedance Accuracy Oh Guru's: A circuit designer has suggested that we can double check the accuracy of our TDR for measuring specific impedances by connecting the TDR's probes directly to a precision resistor of the desired impedance. When I tried it, I got a nice flat line on my scope, but alas, it was not exactly where my instrument said it should be. In addition, different resistors yielded differing amounts of error (4 ohm discrepancy at 50 ohm, 14 ohm discrepancy at 100 ohm). My unit was calibrated by Tektronix only 2 months ago. Therefore, my questions: Is the Electrical Engineer correct; is his procedure accurate? There is no reference to it in any of our TDR manuals, and I think that if such a thing were true, then mention should have been made of it. As Bartels and James would say: "Thanks for your support." ################################################################ TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c ################################################################ To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TechNet <your full name> To unsubscribe: SIGNOFF TechNet ################################################################ Please visit IPC web site (http://jefry.ipc.org/forum.htm) for additional information. For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311 ################################################################ ################################################################ TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c ################################################################ To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TechNet <your full name> To unsubscribe: SIGNOFF TechNet ################################################################ Please visit IPC web site (http://jefry.ipc.org/forum.htm) for additional information. For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311 ################################################################