RE: 50 ohm 75 ohm
Hi, all members, I just came back from a few days bussiness trip to somewhere isolated from this world and didn't anticipate huge amount of reply to my posted question on testing cable impedance. I do appreciate all your suggestions although I am going to try one or two approaches. Thanks regards, Leslie _ Do You Yahoo!? Get your free @yahoo.com address at http://mail.yahoo.com - This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: unsubscribe emc-pstc (without the quotes). For help, send mail to ed.pr...@cubic.com, jim_bac...@monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
Fw: RE: 50 ohm 75 ohm
Posted for Green, Henry henry.gr...@gateway.com: From: Green, Henry henry.gr...@gateway.com Subject: RE: 50 ohm 75 ohm Date: Wed, 14 Jul 1999 09:21:49 -0500 To: 'Leslie Bai' leslie_...@yahoo.com, emc-p...@majordomo.ieee.org I HAVE HAD GREAT SUCCESS USING THE TDR. I FOUND IT QUITE INTERESTING TO NOTE THE VARIATION IN IMPEDANCE OF CABLES THAT WERE SUPPOSEDLY THE SAME. IF YOU HAVE ACCESS TO A TIME DOMAIN REFLECTOMETER, I WOULD SUBMIT THAT THIS IS THE WAY TO GO. IT IS A VERY ACCURATE INSTRUMENT. Henry Green Gateway Regulatory Compliance -Original Message- From: Leslie Bai [mailto:leslie_...@yahoo.com] Sent: Tuesday, July 13, 1999 12:36 PM To: emc-p...@majordomo.ieee.org Subject:50 ohm 75 ohm Dear members, Anyone there can share the experience to measure cables' impedance thus to identify whether a BNC is a 50 ohm or 75 ohm cable. Thanks, Leslie _ Do You Yahoo!? Get your free @yahoo.com address at http://mail.yahoo.com - This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: unsubscribe emc-pstc (without the quotes). For help, send mail to ed.pr...@cubic.com, jim_bac...@monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators). ---End of Original Message- -- Ed Price ed.pr...@cubic.com Electromagnetic Compatibility Lab Cubic Defense Systems San Diego, CA. USA 619-505-2780 List-Post: emc-pstc@listserv.ieee.org Date: 07/14/1999 Time: 08:56:46 Military Avionics EMC Services Our Specialty Also Environmental / Metrology / Reliability -- - This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: unsubscribe emc-pstc (without the quotes). For help, send mail to ed.pr...@cubic.com, jim_bac...@monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
Re: 50 ohm 75 ohm
Leslie Bai wrote: Anyone there can share the experience to measure cables' impedance thus to identify whether a BNC is a 50 ohm or 75 ohm cable. The SECOND simplest way I've found (short of using an SWR meter and a 1:1.5 transformer)_ is as follows: If you have an impedance bridge operating in the high MHz region, you need only measure a quarter wave of coax -- as evidenced by inverting the open circuit at its far end, at any convenient frequency, then measure the capacitive reactance at half the first frequency. Alternatively measure a shorted quarter wave stub -- as evidenced by an infinite or very high impedance reading -- and then look for the inductive reactance at half the frequency. The reactance of a 45 degree line is equal to its characteristic impedance, with the sign depending on the termination. This will not only tell you higher or lower but will identify odd ball coax which might mess up a whole test. Don't ask how I learned THAT. (grin) Good luck! Cortland - This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: unsubscribe emc-pstc (without the quotes). For help, send mail to ed.pr...@cubic.com, jim_bac...@monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
RE: 50 ohm 75 ohm
Bai: If you have a Network Analyzer, just connect the cable to the two port of the analyzer through a BNC-SMA adpator. Measure the reflection coefficient (S11 or S22) and the 75 ohm cable should have a larger reflection. That's my expensive way of doing it.:-) Alternatively, if the two cables are made of the same material, maybe you can check the ratio of outer conductor radius vs. that of inner conductor. The one with larger ratio should have high impedance. Regards Qu Pingyu -Original Message- From: Leslie Bai [SMTP:leslie_...@yahoo.com] Sent: Wednesday, 14 July 1999 1:36 To: emc-p...@majordomo.ieee.org Subject: 50 ohm 75 ohm Dear members, Anyone there can share the experience to measure cables' impedance thus to identify whether a BNC is a 50 ohm or 75 ohm cable. Thanks, Leslie _ Do You Yahoo!? Get your free @yahoo.com address at http://mail.yahoo.com - This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: unsubscribe emc-pstc (without the quotes). For help, send mail to ed.pr...@cubic.com, jim_bac...@monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
Re: 50 ohm 75 ohm
At 10:36 AM 7/13/99 -0700, Leslie Bai wrote: Dear members, Anyone there can share the experience to measure cables' impedance thus to identify whether a BNC is a 50 ohm or 75 ohm cable. Thanks, Leslie Quick and dirty method with a high amount of confidence that you have RG-58 or RG-59 in your hand but not an absolute method? Measure the OD of the cable. RG-59 is *more likely* to be fatter than RG-58. No guarantee though ... - This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: unsubscribe emc-pstc (without the quotes). For help, send mail to ed.pr...@cubic.com, jim_bac...@monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
RE: 50 ohm 75 ohm
You can buy or rent a Time Domain Reflectometer or you can build one yourself as follows. Connect a 50 ohm pulse generator and high impedance scope to one end of the cable and terminate the other end of the cable in 50 ohms. If there is a significant reflection at the far end of the cable as noted on the scope, the impedance is wrong. Change the terminator to 75 ohms to verify. -- From: Leslie Bai [SMTP:leslie_...@yahoo.com] Sent: Tuesday, July 13, 1999 1:36 PM To: emc-p...@majordomo.ieee.org Subject: 50 ohm 75 ohm Dear members, Anyone there can share the experience to measure cables' impedance thus to identify whether a BNC is a 50 ohm or 75 ohm cable. Thanks, Leslie _ Do You Yahoo!? Get your free @yahoo.com address at http://mail.yahoo.com - This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: unsubscribe emc-pstc (without the quotes). For help, send mail to ed.pr...@cubic.com, jim_bac...@monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators). - This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: unsubscribe emc-pstc (without the quotes). For help, send mail to ed.pr...@cubic.com, jim_bac...@monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
50 ohm 75 ohm
Dear members, Anyone there can share the experience to measure cables' impedance thus to identify whether a BNC is a 50 ohm or 75 ohm cable. Thanks, Leslie _ Do You Yahoo!? Get your free @yahoo.com address at http://mail.yahoo.com - This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: unsubscribe emc-pstc (without the quotes). For help, send mail to ed.pr...@cubic.com, jim_bac...@monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
