Like Dan, I have run into various forms of this problem when testing POTS telephone equipment to EN 55024 over the years. EN 55024 has an annex that places limits on the level of the demodulated 1 KHz tone on both the phone line and in the handset. As I recall, those tests are for conducted immunity up to 80 MHz.
To simplify the task of determining whether the headset is the source of the demodulation or just a victim of demodulation elsewhere, it is sometimes helpful to convert your measurements of acoustic power level to measurements of electrical power level. In general, it is easier to create an RF-resistant voltage measurement than to create an RF-resistant acoustic measurement. For most acoustic transducers (both headphones and microphones), there is a very stable relationship between the acoustic level and the corresponding electrical level. For example, a 32 ohm headset speaker, when tested with a single tone, will produce a specific acoustic output level in response to a specific electrical input. A 6 dB increase in the input electrical power will cause a corresponding 6 dB increase in the output sound pressure level. The reverse is true for microphones. I don’t know enough details about the type of headset interface you are trying to evaluate, but perhaps the above method will provide some options for determining the source of the demodulation. If you can temporarily replace the headset with a suitable termination that is unlikely to demodulate RF, you can get some indication of whether the headset in question is the source of the demodulation. Joe Randolph Telecom Design Consultant Randolph Telecom, Inc. 781-721-2848 (USA) <mailto:[email protected]> [email protected] <http://www.randolph-telecom.com> http://www.randolph-telecom.com From: Dan Roman [mailto:[email protected]] Sent: Wednesday, September 05, 2018 3:51 PM To: [email protected] Subject: Re: [PSES] RF immunity - audio noise in headsets Used to run into something similar when testing old telecom POTS lines years back. CISPR 24, if I recall correctly, has a set of criteria for determining a pass for immunity to demodulating the 1kHz. With the POTS lines, the problem was finding a POTS test set that could give you a 1kHz tone dB level measurement that was immune itself. The test sets generally were not designed with immunity in mind. We later switched to a simple battery driven loop current CO simulator setup and software running on the EUT itself to measure any 1kHz tone and report the dB level. Minimizing the external test equipment during immunity testing is always desirable. Are you using the EUT itself to measure the demodulated level or an external device or just using your ears and the headphones? -- Dan Roman, N.C.E. IEEE Senior Member [email protected] <mailto:[email protected]> [email protected] <mailto:[email protected]> On Sep 5, 2018, at 2:00 AM, Amund Westin <[email protected] <mailto:[email protected]> > wrote: Wired headsets and microphones connected to a product, often acts as receiver for induced RF fields. That means you quite often hear the 1kHz modulation tone under the RF immunity tests. This is quite annoying for the user and above a certain level, not acceptable. To avoid such phenomena is quite a big task to conduct. But have anyone of you any experience how to determine if the headsets / microphones or the connected final product is the source to this problem? 3rd. party headsets / microphones have of course different RF immunity performance, and after a lot of testing, you might be able to find headsets / microphones that are does not pick up fields and the hearing audio noise level is acceptable. I assume that the final product may have great level of immunity, but as long the headsets / microphones has poor immunity level, you will have this audio problem anyway. Has anyone been into this problem before? BR 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 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 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]>
