Not saying antenna is at fault. Saying that I don¹t know the characteristics of the SAW filter vs. frequency offset form tuned center and also vs. amplitude.
Also don¹t know how much performance you are asking of the filter. If the intentional signal were at 1 mV/m and you need to reject 3 V/m, you are looking for upwards of 75 dB of out-of-band rejection. That is apportioned amongst the antenna and filter. Ken Javor Phone: (256) 650-5261 From: "James Pawson (U3C)" <ja...@unit3compliance.co.uk> Reply-To: "James Pawson (U3C)" <ja...@unit3compliance.co.uk> Date: Tue, 27 Nov 2018 15:57:16 -0000 To: <EMC-PSTC@LISTSERV.IEEE.ORG> Subject: Re: [PSES] Radiated RF Immunity vs. Radio Module Hi Ken, Thanks for the feedback, I¹ll follow your suggestions! Someone else also suggested that the antenna might be at fault. All the best James From: Ken Javor <ken.ja...@emccompliance.com> Sent: 27 November 2018 15:48 To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Radiated RF Immunity vs. Radio Module Not familiar with possible failure modes of a SAW filter. Don¹t mean breaking it, but how it acts with a strong out-of-band signal, and how far out the stop band works. But the fact that there is complete immunity using coax means that the antenna is allowing enough out-of-band energy in to overload the next stage, SAW filter or no SAW filter. The troubleshoot tests you have outlined are exactly those necessary to map the stop band, and I would do so at various level of out-of-band signal power, because at some point (frequency, amplitude) the SAW filter is failing to deliver required performance. Ken Javor Phone: (256) 650-5261 From: "James Pawson (U3C)" <ja...@unit3compliance.co.uk> Reply-To: "James Pawson (U3C)" <ja...@unit3compliance.co.uk> Date: Tue, 27 Nov 2018 14:02:57 -0000 To: <EMC-PSTC@LISTSERV.IEEE.ORG> Subject: [PSES] Radiated RF Immunity vs. Radio Module Hello, I have a puzzling query today. I¹m testing a product with an integrated radio module for 868MHz Zigbee. The EUT has an internal antenna connected to the UFL connector of the module. This means the wanted signal is provided by an antenna inside the test environment. The standard specifies a +40dB ³link budget². My experience with testing radio modules has been that they are generally fairly robust to radiated interference outside of their tuned frequency. However this module is very much the opposite. When illuminated with 3V/m over most of the 80MHz to 1GHz band communication stops and the RSSI drops. If I bypass the EUT internal antenna and connect a coaxial cable directly to the UFL connector of the EUT RF module from the test generator (attenuated for +40dB link budget) then the product sails through testing at 10V/m! My initial thought was that the input of the module did not have sufficient filtering, resulting in AGC overload. However I¹ve just de-soldered the can and there¹s a SAW filter in line with the RF path (input > SPDT switch > SAW > LNA > radio IC). So I¹m not sure it¹s that any more. I can¹t see this being an module enclosure / system immunity problem because it passes the test at 10V/m when connected direct via coaxial cable (no antennae). Has anyone come across this sort of performance before? Avenues of investigation 1. Put an extra SAW filter in series with the antenna input before the RF module 2. Inject an out of band RF signal into the module and see where it ends up 3. Broken module, swap for a new one 4. Other? >From an approvals perspective, the module as supplied will meet the requirements of 301 489-1 because the manufacturer will have tested it with a coaxial input feed. However when tested with an antennae attached it doesn¹t work under these immunity conditions. It feels like the standard doesn¹t cover this scenario adequately. Frustrating. I¹m contacting the manufacturer in parallel. Thanks in advance for any assistance James (also cross posted to a different forum) - ---------------------------------------------------------------- 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 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 <sdoug...@ieee.org> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org> David Heald <dhe...@gmail.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 <emc-p...@ieee.org> 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 <sdoug...@ieee.org> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org> David Heald <dhe...@gmail.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 <emc-p...@ieee.org> 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 <sdoug...@ieee.org> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org> David Heald <dhe...@gmail.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 <emc-p...@ieee.org> 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 <sdoug...@ieee.org> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
