“I have seen differences of 9 dB on the same measurement on an EUT and comb
generator by different accredited labs! “

 

Doug, I recall this has been the case for decades. There are a lot of
variables to consider, and some are hard to assign a value.  The equipment
has been refined somewhat over those same decades, but the physics remains
unchanged and still produce the same challenges with measurement
uncertainty.

 

It’s only a problem if that uncertainly creates, well… a problem.
Otherwise, EMC measurement is an approximate science, all but impossible to
model accurately, and yet universally accepted as fit for purpose.

 

Ralph

 

From: doug emcesd.com <d...@emcesd.com> 
Sent: October 7, 2024 4:08 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: [PSES] technical musings

 

Hi All,

 

When I was a young engineer at AT&T Bell Labs, about 50 years ago, my
designs had to have an amplitude tolerance of +/- 1/10th dB to meet
requirements (even without computer simulation). So when I came across EMC
topics later on I was initially surprised to see tolerances like +/-2 dB or
more. To me this means either the engineers do not understand the designs,
or (and I think this is the case) there are too many uncontrolled variables
to allow a narrower tolerance. I have seen differences of 9 dB on the same
measurement on an EUT and comb generator by different accredited labs!

 

I personally think that Silicon Valley is the best place to do EMC testing
because there are so many labs, very close to each other, there that they
are driven to be very close to each other in measurement results (otherwise
the outliers would go out of business, quickly). Given a choice, I would
test in Silicon Valley.

 

On a separate topic, I am 77 years old but have the physical and mental
capabilities of a 30 year old from my 50 year experiment to slow the aging
process, which has proven to be a success for me. We often unofficially
discus this after my seminars are finished for the day. On a recent seminar,
the attendees kept me over for two hours after the seminar, questioning me
and taking notes. This is not part of the seminar, but a significant freebie
available to the attendees.

 

I run 3,000+ miles per year, even on 120°F days in the Southern Nevada
desert. Such heat does not even feel stressful to me!  I design my own
hydration. I designed my own nutrition and supplement plans as well. I never
get sick, and am immune from sunburn from one of my supplements,
astaxanthin. This comes from applying science and engineering to my mind and
body. I have read many, many thousands of pages of medical research in my
life and make use of it!

 

Another topic, my classes are focused on finding hidden design flaws in
designs that can cause a manufacturing or field disaster, especially flaws
that result in a problem once in a week or month of significant consequence
that cannot be found by normal engineering methods. Next one is in a few
weeks, mid-October. Contact me if interested.

 

Doug

 
<https://lh4.googleusercontent.com/_HuR3Ky2TF_XhFHyxnYRmiq7nHQldnMsPNYFaLG6k
b5T4y8MeCe-BDC_BscJtSFgszSSjssihHS-pjM3-jwNP8S0CwE-gN8fsRsPkojiAlmpBwb20vIVi
zS-siCUywW_jqrefbVr> 

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