Using the physical circuit, absolutely, which is why the traditional
technique sweeps in peak and then QP detects only the signals above
the QP limit. But with the final IF digitized, and then a software QP
detector transfer function applied, it happens as fast t as the data
processing runs. Which is very fast these days.
--
Ken Javor
Ph: (256) 650-5261
*From: *Karen Burnham <karen.burn...@gmail.com>
*Reply-To: *Karen Burnham <karen.burn...@gmail.com>
*Date: *Friday, October 11, 2024 at 2:56 PM
*To: *<EMC-PSTC@LISTSERV.IEEE.ORG>
*Subject: *Re: [PSES] Technical musings
Ken, isn't there a longer dwell time required for QP detection? I know
most of the standards recommend sweeping in Peak first, then doing QP
only for frequencies of exceedance, just because of the dwell time per
frequency value. I'd be happy to find out I'm wrong about this.
Best,
-=-Karen Burnham
President and Chief Engineer, NCE
EMC United, Inc.
www.emcunited.com <http://www.emcunited.com>
On Fri, Oct 11, 2024 at 1:28 PM Ken Javor
<ken.ja...@emccompliance.com> wrote:
My understanding is that all present-day EMI receivers – and for
quite some time now – have simulated the detectors in software, as
opposed to applying the final IF signal to an actual circuit. The
point being, it takes no more time to do a QP sweep than a peak
sweep. Even an averages sweep takes no longer than a peak sweep.
Seems to me one could run a single sweep, and show the results
using all three detectors, which would help immensely in
identifying the type of signal. And it could facilitate different
limits for all three kinds of detectors, again from a single
sweep. Many of these receivers also have the capability to show
how often such signals occur, which can also assist in determining
how problematic they are.
As Gert says, lots to fix, and I agree with many of his suggestions.
But we also have equipment that can help make more useful, and
more timely measurements.
--
Ken Javor
Ph: (256) 650-5261
*From: *Gert Gremmen F4LDP <g.grem...@cetest.nl>
*Organization: *ce-test, qualified testing bv
*Reply-To: *Gert Gremmen F4LDP <g.grem...@cetest.nl>
*Date: *Friday, October 11, 2024 at 1:48 PM
*To: *<EMC-PSTC@LISTSERV.IEEE.ORG>
*Subject: *Re: [PSES] Technical musings
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 <http://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>
<mailto:j...@woodjohn.uk>
*Sent:* Friday, October 11, 2024 8:58:14 AM
*To:* EMC-PSTC@LISTSERV.IEEE.ORG
<EMC-PSTC@LISTSERV.IEEE.ORG>
<mailto: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.bacher@outlook.comor 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
*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
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Keep trying
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