The transmission line itself doesn't need to be "antenna like", it just needs to be able to excite something else that is
From: James Pawson (U3C) <ja...@unit3compliance.co.uk> Sent: Tuesday, 26 July, 2022 10:51 AM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: [PSES] Transmission line termination impedance -- SI problem yes, EMC problem no? (I posted this in LinkedIn as well but thought I'd float this in front of you learned folks) Transmission line impedance and termination is important for: * Signal integrity = yes * EMC emissions = no (???) Here's my current line of thought: (1) EM Radiation from a transmission line (e.g. PCB microstrip) is dictated by its physical structure (how "antenna like" it is) and the frequency of the signals using it. (2) Assuming the transmission line and the parameters causing reflection are linear, then no new frequency components are being introduced other than those present in the original signal. (3) Energy bouncing backwards and forwards from reflections and mismatches does not cause an additional radiated EM problem that was not already there to begin with. The SI won't be great... Given that active circuitry is used to drive a transmission line (e.g. transistor switches) then there might be non-linear components, meaning point (2) might not hold and new frequency components may be generated. A TX line impedance is matched for maximum power transfer, but the termination only sets where the power is meant to be dissipated. Increased power due to no matching in the transmission line structure increases likelihood of radiation? Maybe a more open transmissions line looks more "antenna like"? Am I missing something? How do I need to think about this problem? All the best James James Pawson Managing Director & EMC Problem Solver Office hours: My mornings are reserved for full attention on consultancy, testing, and troubleshooting activities for our customers' projects. I am otherwise contactable between 1300h to 1730h from Monday to Friday. For inquiries, bookings, and testing updates please send us an email on he...@unit3compliance.co.uk<mailto:he...@unit3compliance.co.uk> or call 01274 911747. Our lead times for testing and consultancy are typically 4-5 weeks. Unit 3 Compliance Ltd EMC : Environmental & Vibration : Electrical Safety : CE & UKCA : Consultancy www.unit3compliance.co.uk<http://www.unit3compliance.co.uk/> | ja...@unit3compliance.co.uk<mailto:ja...@unit3compliance.co.uk> +44(0)1274 911747 | +44(0)7811 139957 2 Wellington Business Park, New Lane, Bradford, BD4 8AL Registered in England and Wales # 10574298 ________________________________ [AVG logo]<https://www.avg.com/internet-security> This email has been checked for viruses by AVG antivirus software. www.avg.com<https://www.avg.com/internet-security> - ---------------------------------------------------------------- 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 <emc-p...@ieee.org<mailto:emc-p...@ieee.org>> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html 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: Mike Cantwell <mcantw...@ieee.org<mailto:mcantw...@ieee.org>> For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org<mailto:j.bac...@ieee.org>> David Heald <dhe...@gmail.com<mailto:dhe...@gmail.com>> ________________________________ 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 <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html 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: Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com> _________________________________________________ To unsubscribe from the EMC-PSTC list, click the following link: https://listserv.ieee.org/cgi-bin/wa?SUBED1=EMC-PSTC&A=1
