Brian, Two things immediately come to mind:
1. A Faraday Enclosure depends on a continuous conductive seal at all seams; did the powder coat somehow cause a break in the conductivity, even if it is only paper-thin? 2. Slot Antenna: Measure the gap length between fasteners. Use this measurement of the frequencies of concern. You may have created a "slot antenna", roughly a half-wavelength (λ/2) slot, which is a direct dual or complement of a dipole antenna. Perfect for a certain frequency. Mitigation can include several options: adding extra screws to split gaps into shorter sections, masking the powder coating in critical zones if corrosion isn't an issue, and employing conductive elastomer gaskets or fingerstock solely on bare metal parts. ~Doug Douglas E Powell Founder & Principal Consultant Vertex Compliance Consulting <https://bit.ly/45BXk3Y> (VertexCC) Laporte, Colorado, USA LinkedIn <https://www.linkedin.com/in/realdougpowell/> Colorado Registered Business | Entity ID: 20191778678 (UTC-06:00, US-MDT) On Thu, Jan 29, 2026 at 12:59 PM Jim Bacher, WB8VSU <[email protected]> wrote: > Brian, I had something similar happen years ago. Primary issue was the > mechanical guys decided to save money and not use lock washers. > > > Jim Bacher, WB8VSU > [email protected] > JBRC Consulting LLC > Product EMC & Regulatory Consultant > https://www.trc.guru/ <https://trc.guru/> business email:[email protected] > IEEE Life Senior Member > > On January 29, 2026 2:52:22 PM Brian Gregory <[email protected]> > wrote: > >> Hi folks, >> >> Our bare-metal prototype passed FCC Class B RE with flying colors; 8-12 >> dB margin. >> Now, a fairly similar unit (hey, they're prototypes) whose enclosure is >> power coated is now failing by 10-20 dB. The worst failures are at low >> frequencies, under 50 MHz, apparently. >> >> Is there anything more complicated we should look at apart from the >> powder coat mask not working well enough, such that covers and side panels >> aren't properly grounded with all that epoxy ? What else could account >> for this difference? >> >> thanks, >> >> Colorado Brian >> ------------------------------ >> >> 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: >> https://www.mail-archive.com/[email protected]/ >> >> Website: https://ewh.ieee.org/soc/pses/ >> Instructions: https://ewh.ieee.org/soc/pses/list.html (including how to >> unsubscribe) <https://ewh.ieee.org/soc/pses/list.html> >> List rules: >> https://pses.ieee.org/wp-content/uploads/2024/12/EM-PSTC-List-Rules.pdf >> >> For help, send mail to the list administrators: >> Mike Sherman at: [email protected] >> Rick Linford at: [email protected] >> >> For policy questions, send mail to: >> Jim Bacher at: [email protected] >> ------------------------------ >> >> To unsubscribe from the EMC-PSTC list, click the following link: >> https://listserv.ieee.org/cgi-bin/wa?SUBED1=EMC-PSTC&A=1 >> > > > ------------------------------ > > 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: > https://www.mail-archive.com/[email protected]/ > > Website: https://ewh.ieee.org/soc/pses/ > Instructions: https://ewh.ieee.org/soc/pses/list.html (including how to > unsubscribe) <https://ewh.ieee.org/soc/pses/list.html> > List rules: > https://pses.ieee.org/wp-content/uploads/2024/12/EM-PSTC-List-Rules.pdf > > For help, send mail to the list administrators: > Mike Sherman at: [email protected] > Rick Linford at: [email protected] > > For policy questions, send mail to: > Jim Bacher at: [email protected] > ------------------------------ > > To unsubscribe from the EMC-PSTC list, click the following link: > https://listserv.ieee.org/cgi-bin/wa?SUBED1=EMC-PSTC&A=1 > - ---------------------------------------------------------------- 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: https://www.mail-archive.com/[email protected]/ Website: https://ewh.ieee.org/soc/pses/ Instructions: https://ewh.ieee.org/soc/pses/list.html (including how to unsubscribe) List rules: https://pses.ieee.org/wp-content/uploads/2024/12/EM-PSTC-List-Rules.pdf For help, send mail to the list administrators: Mike Sherman at: [email protected] Rick Linford at: [email protected] For policy questions, send mail to: Jim Bacher: <[email protected]> _________________________________________________ To unsubscribe from the EMC-PSTC list, click the following link: https://listserv.ieee.org/cgi-bin/wa?SUBED1=EMC-PSTC&A=1
