We're running the UL EMC software package. Here are 2 new clues to the puzzle:
1. If I go into the Measurement Setup editing screen and change the pre-selector attenuation to Bypass the discontinuities go away. 2. The 14MHz spacing of the discontinuities becomes 17MHz if I change the # of segments for the range from 12 to 10 (200MHz - 30MHz = 170MHz then divide by 12 = 14.17MHz and divide by 10 = 17MHz). >From this I conclude that... a) the spacing of the discontinuities is related to the setup, so it's definitely not a narrowband source summing with a broadband source. b) the problem is either in the preselector, or in its interaction with the SA or the UL software. Does anybody have any further guesses or experiences with this sort of thing? Thanks, Jim Eichner, P.Eng. Compliance Engineering Manager Xantrex Technology Inc. e-mail: [email protected] web: www.xantrex.com Confidentiality Notice: This email message, including any attachments, is for the sole use of the intended recipient(s) and may contain confidential and privileged information. Any unauthorized review, use, disclosure or distribution is prohibited. If you are not the intended recipient, please contact the sender by reply e-mail and destroy all copies of the original message. From: Powell, Doug [mailto:[email protected]] Sent: Monday, May 14, 2007 1:05 PM To: Jim Eichner; EMC PSTC Subject: RE: Pre-selector trouble? Hi Jim, It is likely that you have two sources of RF noise. The emission you are seeing the sum of both. I believe one is narrowband the other is broadband. The broadband could be from a number of sources but is usually not too difficult to suppress. The trick is to identify all the sources. It looks as if the narrow band emissions are spaced exactly 14 MHz apart >from one another. So the fundamental of the emitter is running at 14 MHz. Find out what it is and take care of that at the source if you are able. Regards, -doug From: [email protected] [mailto:[email protected]] On Behalf Of Jim Eichner Sent: Monday, May 14, 2007 1:27 PM To: EMC PSTC Subject: Pre-selector trouble? We're running a radiated scan in the 30-200MHz range on a power conversion product that has broadband noise throughout. The data is showing evenly spaced discontinuities at 44MHz, 58MHz, 72MHz, and 86MHz. There may be others at higher frequency but if so they are subtle. By "discontinuity" I mean the data takes a sudden jump upwards, with the magnitude of the jump being different at each frequency. The testing is being done with the typical HP 856XX rack that everyone has. Does anybody have any ideas what the problem could be? I suspect our aging HP85685A pre-selector, based on the nature of the issue we're seeing, and on its history of unreliable operation. Thanks for your help, Jim Eichner, P.Eng. Compliance Engineering Manager Xantrex Technology Inc. e-mail: [email protected] web: www.xantrex.com Confidentiality Notice: This email message, including any attachments, is for the sole use of the intended recipient(s) and may contain confidential and privileged information. Any unauthorized review, use, disclosure or distribution is prohibited. If you are not the intended recipient, please contact the sender by reply e-mail and destroy all copies of the original message. - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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