Re: [PSES] Technical musings

[John Woodgate]

Yes, there are advantages of improving MU, but they do not outweigh the 
cost of a major improvement.

On 2024-10-11 19:48, Gert Gremmen F4LDP wrote:
Why using numbers (in dBuV/m) if the MU is 200-400 % ? Using number 
assumes a defined and known uncertainty.

All this experiences calls out for a more strict measurement set-up, 
with extensive cable lay-out description, EUT set-up
a uniform test site (5 meter FAR ?) , standard antennas, regular 
calibration and verification ahead on each test ,
an intelligent site attenuation calculation per frequency range (such 
as 30-100 100-300 and 300-1000 MHz) and more, if well done resulting
in a lower MU of the total measurement. Focus shall be on 
reproducibility, a 6 dB offset is not that of a problem als long as we 
are all 6 dB off.
Seen the fact that the current measurements do result in a (more or 
less) satisfactorily EMC situation in spite of excessive variations in 
results, we may assume that the current emission limits are on the 
safe side (= too low), and can be adjusted (say 5 dB) upwards, once a 
better overall MU is obtained, finally resulting in cheaper EMC 
testing, cheaper EUT production, and less excessive radiation = less 
interference.
As the determining value for compliance is a QP-value, additional 
attention shall be paid to the peak pre-scan dwell times (actually 
defining the frequencies to be measured) and EUT emission cycling 
times, in order to find all qualifying frequencies for QP-evaluation, 
an aspect that is too often overlooked.
It won't be easy to catch up for all these, but didn't we get to Mars 
too ?

Gert Gremmen

On 11-10-2024 20:23, John Woodgate wrote:

Yes, there's not only the intractable near-field issue, but all the 
EM influences between the various pieces of equipment. This all adds 
to the uncertainty and irrepeatable results.

On 2024-10-11 18:08, doug emcesd.com wrote:
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: d...@dsmith.org
Website: http://dsmith.org
------------------------------------------------------------------------
*From:* John Woodgate <j...@woodjohn.uk>
*Sent:* Friday, October 11, 2024 8:58:14 AM
*To:* EMC-PSTC@LISTSERV.IEEE.ORG <EMC-PSTC@LISTSERV.IEEE.ORG>
*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

ja.bac...@outlook.com <mailto:ja.bac...@outlook.com> or 
j.bac...@ieee.org <mailto:j.bac...@ieee.org>

*From:*John Woodgate <j...@woodjohn.uk> <mailto:j...@woodjohn.uk>
*Sent:* Wednesday, October 09, 2024 4:18 PM
*To:* EMC-PSTC@LISTSERV.IEEE.ORG <mailto:EMC-PSTC@LISTSERV.IEEE.ORG>
*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://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 EMC-PSTC@LISTSERV.IEEE.ORG 
<mailto:EMC-PSTC@LISTSERV.IEEE.ORG>

All emc-pstc postings are archived and searchable on the web at:
https://www.mail-archive.com/emc-pstc@listserv.ieee.org/ 
<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: msherma...@comcast.net <mailto:msherma...@comcast.net>
Rick Linford at: linf...@ieee.org <mailto:linf...@ieee.org>

For policy questions, send mail to:
Jim Bacher at: j.bac...@ieee.org <mailto:j.bac...@ieee.org>

------------------------------------------------------------------------

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 EMC-PSTC@LISTSERV.IEEE.ORG

All emc-pstc postings are archived and searchable on the web at:
https://www.mail-archive.com/emc-pstc@listserv.ieee.org/ 
<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: msherma...@comcast.net
Rick Linford at: linf...@ieee.org

For policy questions, send mail to:
Jim Bacher at: j.bac...@ieee.org

------------------------------------------------------------------------

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-PSTC@LISTSERV.IEEE.ORG

All emc-pstc postings are archived and searchable on the web at:
https://www.mail-archive.com/emc-pstc@listserv.ieee.org/

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://ewh.ieee.org/soc/pses/listrules.html

For help, send mail to the list administrators:
Mike Sherman at: msherma...@comcast.net
Rick Linford at: linf...@ieee.org

For policy questions, send mail to:
Jim Bacher at: j.bac...@ieee.org

------------------------------------------------------------------------

To unsubscribe from the EMC-PSTC list, click the following link: 
https://listserv.ieee.org/cgi-bin/wa?SUBED1=EMC-PSTC&A=1

--
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 EMC-PSTC@LISTSERV.IEEE.ORG

All emc-pstc postings are archived and searchable on the web at:
https://www.mail-archive.com/emc-pstc@listserv.ieee.org/

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://ewh.ieee.org/soc/pses/listrules.html

For help, send mail to the list administrators:
Mike Sherman at: msherma...@comcast.net
Rick Linford at: linf...@ieee.org

For policy questions, send mail to:
Jim Bacher at: j.bac...@ieee.org

------------------------------------------------------------------------

To unsubscribe from the EMC-PSTC list, click the following link: 
https://listserv.ieee.org/cgi-bin/wa?SUBED1=EMC-PSTC&A=1


--
Independent Expert on CE marking
EMC Consultant
Electrical Safety Consultant

--
OOO - Own Opinions Only
Best Wishes
John Woodgate
Keep trying


--
This email has been checked for viruses by AVG antivirus software.
www.avg.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-PSTC@LISTSERV.IEEE.ORG

All emc-pstc postings are archived and searchable on the web at:
https://www.mail-archive.com/emc-pstc@listserv.ieee.org/

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: msherma...@comcast.net
Rick Linford at: linf...@ieee.org

For policy questions, send mail to:
Jim Bacher:  <j.bac...@ieee.org>
_________________________________________________
To unsubscribe from the EMC-PSTC list, click the following link: 
https://listserv.ieee.org/cgi-bin/wa?SUBED1=EMC-PSTC&A=1