Amund, you’re definitely on the right track in troubleshooting this issue. I agree with Ken Javor that, because of the length of cable, you’ll want to fix the probe at the same location every time you go to troubleshoot.
Let me also add these points. (1) Make sure the fan cable is routed away from all others and in close proximity to any chassis or enclosure, so any common mode currents have a chance to flow back to their source through the chassis. (2) Make sure any ferrites used are of sufficient impedance at 145 MHz. The 5 dB reduction was pretty good, but by wrapping the cable through the core once more, you may be able to do better. (3) Fair-Rite #61, 31 or possibly 43 material ought to work pretty well at 145 MHz. As always, it’s best to reduce the energy of the source AT the source through filtering, better PC board layout/stack-up, etc. Cheers, Ken _______________________ I'm here to help you succeed! Feel free to call or email with any questions related to EMC or EMI troubleshooting - at no obligation. I'm always happy to help! Kenneth Wyatt Wyatt Technical Services LLC 56 Aspen Dr. Woodland Park, CO 80863 Phone: (719) 310-5418 Web Site <http://www.emc-seminars.com/> | Blog <https://design-4-emc.com/> The EMC Blog (EDN) <https://www.edn.com/electronics-blogs/4376432/The-EMC-Blog> Subscribe to Newsletter <http://www.emc-seminars.com/Newsletter/Newsletter.html> Connect with me on LinkedIn <https://www.linkedin.com/in/kennethwyatt/> > On Jun 9, 2021, at 7:15 AM, Ken Javor <[email protected]> wrote: > > Agree. But at 145 MHz, cable is electrically long. In order to compare > before and after, need to measure at exactly the same location, on account of > standing waves, unless you used an absorbing clamp, in which case no issue. > > > Ken Javor > Phone: (256) 650-5261 > > > From: Amund Westin <[email protected] > <x-msg://12/[email protected]>> > Reply-To: Amund Westin <[email protected] > <x-msg://12/[email protected]>> > Date: Wed, 9 Jun 2021 10:38:50 +0200 > To: <[email protected] <x-msg://12/[email protected]>> > Subject: [PSES] Radiated emission - troubleshooting with current clamp > > We did some EMC testing last week (radiated emission in a chamber) on a > ventilation system with two fans. It exceeded the limits on 145MHz. > > Then outside the camber, we shut down the fans, we found the 145MHz on a bus > line from a controller (3rd part product). Connecting the fans back again, > the noise increase with increasing speed on the fans. Broadband noise at > 145MHz. > > The troubleshooting process have been carried out outside the chamber (due to > costs). We had a current clamp connected to a spectrum analyzer and measured > every internal cable. > 145MHz was only visible on the bus line and the cables to the fans (which are > 2 meters long, unshielded). > > We inserted a CM choke on the bus line, and the 145MHz on the fan cable > decreased by approximate 5 dB (current clamp meas.). What this would mean in > decreased level under a radiated test, it’s hard to say. > > We are planning to check it out in the chamber next time. > During that exercise, we will also prepare a better bonding of the fan cables > to the chassis in order to reduse the radiated fields from the fan cables. > Also have a shielded harness. > > Do you agree that the current clamp + spectrum analyzer, is a good tool for > finding the noise and the wires that may act as antennas? > > > Best regards > Amund > > > > - > ---------------------------------------------------------------- > > This message is from the IEEE Product Safety Engineering Society emc-pstc > discussion list. 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To post a message to the list, send your e-mail to > <[email protected] <mailto:[email protected]>> > All emc-pstc postings are archived and searchable on the web at: > http://www.ieee-pses.org/emc-pstc.html > <http://www.ieee-pses.org/emc-pstc.html> > Attachments are not permitted but the IEEE PSES Online Communities site at > http://product-compliance.oc.ieee.org/ > <http://product-compliance.oc.ieee.org/> can be used for graphics (in > well-used formats), large files, etc. > Website: http://www.ieee-pses.org/ <http://www.ieee-pses.org/> > Instructions: http://www.ieee-pses.org/list.html (including how to > unsubscribe) <http://www.ieee-pses.org/list.html> > List rules: http://www.ieee-pses.org/listrules.html > <http://www.ieee-pses.org/listrules.html> > For help, send mail to the list administrators: > Scott Douglas <[email protected] <mailto:[email protected]>> > Mike Cantwell <[email protected] <mailto:[email protected]>> > For policy questions, send mail to: > Jim Bacher <[email protected] <mailto:[email protected]>> > David Heald <[email protected] <mailto:[email protected]>> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
