Richard, For shielded ports/cables the method used should be the current clamp method as described in C.1.2 of Annex C, EN 55022:1998. The ISN is used for unshielded ports/cables. We had the same problem of failing conducted emissions when we used an ISN. When you put a current clamp on a shielded cable you are seeing the data return currents on the shield. Connecting the shield to earth through a 150 ohm resistor as specified in C.1.2 compensates for that. At least that is my understanding; maybe others have more insight into this. Bill Fleury
-----Original Message----- From: Richard Lee [mailto:r...@terawave.com] Sent: Monday, April 23, 2001 12:31 PM To: emc-p...@ieee.org Subject: ISN or Current probe method on telecommunication ports? Dear Colleague, Does anybody have done any conducted emission test on telecommunication ports per EN55022 1998 standard requirement? Currently, we have performed a conducted emission test of our product on the shielded telecom port by using ISN and current probe methods, and the results of both tests are totally different. With ISN method, the EUT failed the conducted emission on shielded telecom port by 20 dB. With current probe method, our product passed the conducted test with good margin. We don't know what is the theory behind the ISN and Current probe methods? Can anybody explain to us or advise what we need to do to pass the conducted emission test? Can the test lab accept the current probe method test data or we have to meet both limits of voltage and current requirements that listed in table 4 of CISPR. 22 1997 standard? Our product used all shielded cables on telecom ports. Per Clause 9.5.3.3 & 9.5.3.4 of CISPR. 22 1997, both methods are allowed for telecom port testing. Any suggestions or feedback will be very appreciated. Thanks in advance! Richard Lee Compliance Engineer ------------------------------------------------------------------ Terawave Communications, Inc. 30680 Huntwood, Ave. Hayward, CA 94544 Tel: 510-401-6590 Fax: 510-401-6628 www.terawave.com
