If you don't have a network analyzer, you can a good handle on the impedance using a signal generator, scope and a resistor. Make sure the electrical length of the cable is much larger (10X) than the rise time of the generator. Load one end with 100 ohms or so and connect the generator and scope at the other end. If the impedance is more or less than the resistor value, you will see reflections from the resistor. Change the resistor value until the reflections are minimized and that is the impedance.
Richard Woods ---------- From: David Spencer [SMTP:dspen...@oresis.com] Sent: Thursday, January 11, 2001 12:42 PM To: 'William D'Orazio'; EMC Posting (E-mail) Subject: RE: Zo Hi William, This is a dynamic quantity dependent on the size of the wire, number of twists, and frequency range of interest. You can get a lot of good information from the web pages of various twisted pair cable manufacturers. The normal impedance for twisted pair sold as CAT 3 and CAT 5 (and others) is 100 ohms for a given frequency range, 1-16 MHz for CAT3 and 1-100MHz for CAT5. There are others available (E1 telephony @ 120 ohms.) New flavors of twisted pair are extending the frequency range up to 350MHz. If you have access to a network analyzer, you can probably characterize a given twist/inch of xxASG wire for your frequency range of interest. Hope this helps, Dave Spencer Oresis Communications -----Original Message----- From: William D'Orazio [mailto:dora...@cae.ca] Sent: Thursday, January 11, 2001 6:49 AM To: EMC Posting (E-mail) Subject: Zo Does anybody know the characteristic impedance of a twisted pair? Thanks in advance, <<...OLE_Obj...>> William D'Orazio CAE Electronics Ltd. Electrical System Designer Phone: (514) 341-2000 (X4555) Fax: (514)340-5552 Email: dora...@cae.ca ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson: pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson: pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson: pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
