Hi Amund,
Narrowband or broadband noise? If broadband and you zoom in to the noise on the analyser, is it made up of separate peaks? What is the spacing between the peaks? Try using a near field probe to zoom in on the emissions - https://www.unit3compliance.co.uk/graphical-guide-to-emc-near-field-probing/ All the best James James Pawson Managing Director & EMC Problem Solver Unit 3 Compliance Ltd EMC : Environmental & Vibration : Electrical Safety : CE & UKCA : Consultancy <http://www.unit3compliance.co.uk/> www.unit3compliance.co.uk | <mailto:[email protected]> [email protected] +44(0)1274 911747 | +44(0)7811 139957 2 Wellington Business Park, New Lane, Bradford, BD4 8AL Registered in England and Wales # 10574298 From: Amund Westin <[email protected]> Sent: 05 May 2022 09:50 To: [email protected] Subject: [PSES] Chasing a specific frequency During a radiated emission test, we have a problem with one specific frequency, 63MHz. Not exactly 63.00MHz but like 63.03406…. We have calculated all combinations of intermodulation products from oscillators on the pcb, but no one match the 63MHz. There are a lots of DC/DC converters on the board, and I suspect low switching frequencies (≈1MHz) may be the source and problem. How this low frequency signal became 63MHz noise, it must be (could be … or?) a combination of harmonics and layout circuitry that optimize unwanted antenna performance and then result in a powerful noise component at 63MHz. At this stage, we have not investigated the trace layouts or the layers stacking of the pcb. We have done some introduction of clean power (batteries) and in the same time, bypassed DCDC converters to observe the difference in noise spectrum. On the right track? BR Amund - ---------------------------------------------------------------- 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] <mailto:[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) <http://www.ieee-pses.org/list.html> List rules: 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 email has been checked for viruses by AVG. https://www.avg.com - ---------------------------------------------------------------- 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]>
