A criteria I have seen and agree with is that the distance from the EUT to the antenna be 10x the size of the EUT to insure the antenna is seeing a uniform field so it’s calibration is valid. This is not the same as being in the far field. This is a big issue at 3 meters.
I have significant issues with many, if not most standards I have read. For instance, the people who wrote IEC 61000-4-4 did not understand the way the "capacitive" clamp works. It is also an "inductive" clamp and as a result it is directive and more energy is sent to the auxiliary equipment than to the EUT, there is no excuse for this. the clamp is positioned backwards in the standard!!!! I have been pointing this out for 30 years now to my clients and others. Here is a link to a paper I wrote on this almost 30 years ago: https://emcesd.com/pdf/esd96-w.pdf In my opinion, neither the clamp nor the standard accurately describe actual EFT although in later years some progress has been made, not nearly enough though. I see problems like this in many standards I read. Another problem that is much harder to control happens over in the ESD side. My personal discharge at 4 kV holding a small piece of metal with a measurement chain with 5 GHz bandwidth has a peak current twice what the standard calls for but the follow-on "hump" is more of a straight line down to the horizontal axis much faster than the standard calls for containing a lot less energy. I think this is due to the fact I have less capacitance (surface area, I am about two meters tall but on the skinny side from running 3,000 miles a year) that what was used for the standard which is probably closer to average than me. I have no idea how to account for variability between people and the actual environment they are in when an ESD event happens. Doug Smith Sent from my iPhone IPhone: 408-858-4528 Office: 702-570-6108 Email: [email protected] Website: http://dsmith.org ________________________________ From: John Woodgate <[email protected]> Sent: Friday, October 11, 2024 8:58:14 AM To: [email protected] <[email protected]> Subject: Re: [PSES] Technical musings Thanks, Jim. I wondered whether there was anything other than the 'near-field thicket' involved. Measurement results in the near field can be reliably reproduced only in absolutely identical test set-ups. This is not compatible with 'standardization'. On 2024-10-11 16:48, Jim Bacher wrote: John, you ask why the difference in levels measured between test distances of 3 meters and 10 meters. It’s fairly common for a device to fail at frequencies below 125 MHz at 3 Meter test distance and then pass at a 10 Meter test distance. Besides all the other possible factors (such as was a different chamber and test equipment used), the question becomes, was it a Near Field or Far Field RF signal that was being measured? Near Field RF levels drop faster than Far Field RF Levels. The problem with a 3 Meter test distance is the frequency being measured might be impacted by Near Field, verses Far Field only measurement at 10 Meters. I have read a number of papers that claim different wave lengths for the Near Field effect. The values I have seen are between 1 and 3 wave lengths (with RF think wave lengths). I suspect it is system dependent and typically 1 to 2 wavelengths and I suspect the primary reason for the effect between the two measurement distances. Here are the approximate possible frequency ranges impacted by Near Field at a test distance of 3 Meters: Three wavelength signal: RF levels up to 280 MHz Two wavelength signal: RF levels up to 140 MHz One wavelength signal: RF levels up to 70 MHz As far as I am concerned 10 meters is the better test distance as it is in the Far Field for the frequencies between 30 MHz and 1 GHz. Although 30 Mhz is close to one wavelength at 10 Meters. Jim Bacher, WB8VSU [email protected]<mailto:[email protected]> or [email protected]<mailto:[email protected]> From: John Woodgate <[email protected]><mailto:[email protected]> Sent: Wednesday, October 09, 2024 4:18 PM To: [email protected]<mailto:[email protected]> Subject: [PSES] Technical musings Reply to Derek @ LF Research, because his post is labelled as SPAM. Yes, adding OATS is always healthy.😉 Is there an accepted explanation for the '3 m excess'? The published results are consistent with the field being diffuse (that term is from acoustics: I'm not sure how widely it's used in EMC circles), i.e the resultant of a large number of direct, reflected and diffracted rays. It is hardly surprising: a cuboid space is 'ideal' for producing a diffuse field above 'eigentone' wavelengths. This might create at least a 3 dB increase over 'inverse square' and maybe more. I suppose things get complicated at wavelengths that cannot be called 'short'. Has anyone tried a spherical chamber? If that's too difficult, a 'quartic sphere [(x,y,z)^4 = r^4, like a Swedish traffic circle] has noticeably rounded corners and edges, so might be close enough for a useful improvement. -- OOO - Own Opinions Only Best Wishes John Woodgate Keep trying [https://s-install.avcdn.net/ipm/preview/icons/icon-envelope-tick-green-avg-v1.png]<https://urldefense.proofpoint.com/v2/url?u=http-3A__www.avg.com_email-2Dsignature-3Futm-5Fmedium-3Demail-26utm-5Fsource-3Dlink-26utm-5Fcampaign-3Dsig-2Demail-26utm-5Fcontent-3Demailclient&d=DwMDaQ&c=euGZstcaTDllvimEN8b7jXrwqOf-v5A_CdpgnVfiiMM&r=c9NR2mGfldry-2pM9Bbuww&m=DRzvQBMpj-WwD6xyUgBid8ppyv7j7BkK85n49Ul8bwfkM-CO9V55PArJsLox-xG9&s=1mS2sew-kVjleZxEGVyBEMs2HQ_Mc4tcIFSvC_qxLCU&e=> Virus-free.www.avg.com<https://urldefense.proofpoint.com/v2/url?u=http-3A__www.avg.com_email-2Dsignature-3Futm-5Fmedium-3Demail-26utm-5Fsource-3Dlink-26utm-5Fcampaign-3Dsig-2Demail-26utm-5Fcontent-3Demailclient&d=DwMDaQ&c=euGZstcaTDllvimEN8b7jXrwqOf-v5A_CdpgnVfiiMM&r=c9NR2mGfldry-2pM9Bbuww&m=DRzvQBMpj-WwD6xyUgBid8ppyv7j7BkK85n49Ul8bwfkM-CO9V55PArJsLox-xG9&s=1mS2sew-kVjleZxEGVyBEMs2HQ_Mc4tcIFSvC_qxLCU&e=> ________________________________ 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: https://www.mail-archive.com/[email protected]/<https://urldefense.proofpoint.com/v2/url?u=https-3A__www.mail-2Darchive.com_emc-2Dpstc-40listserv.ieee.org_-2520&d=DwMDaQ&c=euGZstcaTDllvimEN8b7jXrwqOf-v5A_CdpgnVfiiMM&r=c9NR2mGfldry-2pM9Bbuww&m=DRzvQBMpj-WwD6xyUgBid8ppyv7j7BkK85n49Ul8bwfkM-CO9V55PArJsLox-xG9&s=KHqxqauZ-Wo72eklWrHPsAu1EpHSO-JOzSozY4ENmiI&e=> Website: https://ewh.ieee.org/soc/pses/ <https://urldefense.proofpoint.com/v2/url?u=https-3A__ewh.ieee.org_soc_pses_&d=DwMDaQ&c=euGZstcaTDllvimEN8b7jXrwqOf-v5A_CdpgnVfiiMM&r=c9NR2mGfldry-2pM9Bbuww&m=DRzvQBMpj-WwD6xyUgBid8ppyv7j7BkK85n49Ul8bwfkM-CO9V55PArJsLox-xG9&s=zxak5bRzx3Usx44Hb4zps9n_qie5O0B1mv1llELw9Ko&e=> Instructions: https://ewh.ieee.org/soc/pses/list.html (including how to unsubscribe)<https://urldefense.proofpoint.com/v2/url?u=https-3A__ewh.ieee.org_soc_pses_list.html&d=DwMDaQ&c=euGZstcaTDllvimEN8b7jXrwqOf-v5A_CdpgnVfiiMM&r=c9NR2mGfldry-2pM9Bbuww&m=DRzvQBMpj-WwD6xyUgBid8ppyv7j7BkK85n49Ul8bwfkM-CO9V55PArJsLox-xG9&s=j8oWQyHHA9oLAIevzpYBpn1HJ8PAaG4HzXFD6gMtTC8&e=> List rules: https://ewh.ieee.org/soc/pses/listrules.html<https://urldefense.proofpoint.com/v2/url?u=https-3A__ewh.ieee.org_soc_pses_listrules.html&d=DwMDaQ&c=euGZstcaTDllvimEN8b7jXrwqOf-v5A_CdpgnVfiiMM&r=c9NR2mGfldry-2pM9Bbuww&m=DRzvQBMpj-WwD6xyUgBid8ppyv7j7BkK85n49Ul8bwfkM-CO9V55PArJsLox-xG9&s=uwSuet8sdh4etyjqamJShwYGsP4lmUZVrSokH9-iTtY&e=> For help, send mail to the list administrators: Mike Sherman at: [email protected]<mailto:[email protected]> Rick Linford at: [email protected]<mailto:[email protected]> For policy questions, send mail to: Jim Bacher at: [email protected]<mailto:[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<https://urldefense.proofpoint.com/v2/url?u=https-3A__listserv.ieee.org_cgi-2Dbin_wa-3FSUBED1-3DEMC-2DPSTC-26A-3D1&d=DwMDaQ&c=euGZstcaTDllvimEN8b7jXrwqOf-v5A_CdpgnVfiiMM&r=c9NR2mGfldry-2pM9Bbuww&m=DRzvQBMpj-WwD6xyUgBid8ppyv7j7BkK85n49Ul8bwfkM-CO9V55PArJsLox-xG9&s=doJECholXh_UoUqrICwrJImDUWe3rWt_TzQ0PYI_1C8&e=> -- OOO - Own Opinions Only Best Wishes John Woodgate Keep trying ________________________________ 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]/<https://urldefense.proofpoint.com/v2/url?u=https-3A__www.mail-2Darchive.com_emc-2Dpstc-40listserv.ieee.org_&d=DwMDaQ&c=euGZstcaTDllvimEN8b7jXrwqOf-v5A_CdpgnVfiiMM&r=c9NR2mGfldry-2pM9Bbuww&m=DRzvQBMpj-WwD6xyUgBid8ppyv7j7BkK85n49Ul8bwfkM-CO9V55PArJsLox-xG9&s=2oTwsix6oaOPyv0IIAbT8g3bAKkqdYtRRL8yvLnDmyc&e=> Website: https://ewh.ieee.org/soc/pses/ <https://urldefense.proofpoint.com/v2/url?u=https-3A__ewh.ieee.org_soc_pses_&d=DwMDaQ&c=euGZstcaTDllvimEN8b7jXrwqOf-v5A_CdpgnVfiiMM&r=c9NR2mGfldry-2pM9Bbuww&m=DRzvQBMpj-WwD6xyUgBid8ppyv7j7BkK85n49Ul8bwfkM-CO9V55PArJsLox-xG9&s=zxak5bRzx3Usx44Hb4zps9n_qie5O0B1mv1llELw9Ko&e=> Instructions: https://ewh.ieee.org/soc/pses/list.html (including how to unsubscribe)<https://urldefense.proofpoint.com/v2/url?u=https-3A__ewh.ieee.org_soc_pses_list.html&d=DwMDaQ&c=euGZstcaTDllvimEN8b7jXrwqOf-v5A_CdpgnVfiiMM&r=c9NR2mGfldry-2pM9Bbuww&m=DRzvQBMpj-WwD6xyUgBid8ppyv7j7BkK85n49Ul8bwfkM-CO9V55PArJsLox-xG9&s=j8oWQyHHA9oLAIevzpYBpn1HJ8PAaG4HzXFD6gMtTC8&e=> List rules: https://ewh.ieee.org/soc/pses/listrules.html<https://urldefense.proofpoint.com/v2/url?u=https-3A__ewh.ieee.org_soc_pses_listrules.html&d=DwMDaQ&c=euGZstcaTDllvimEN8b7jXrwqOf-v5A_CdpgnVfiiMM&r=c9NR2mGfldry-2pM9Bbuww&m=DRzvQBMpj-WwD6xyUgBid8ppyv7j7BkK85n49Ul8bwfkM-CO9V55PArJsLox-xG9&s=uwSuet8sdh4etyjqamJShwYGsP4lmUZVrSokH9-iTtY&e=> For help, send mail to the list administrators: Mike Sherman at: [email protected]<mailto:[email protected]> Rick Linford at: [email protected]<mailto:[email protected]> For policy questions, send mail to: Jim Bacher at: [email protected]<mailto:[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://ewh.ieee.org/soc/pses/listrules.html 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
