Re: [PSES] Field probe calibration

[John Woodgate]

Re robust designs. There is also a powerful inertia effect. If you make 
a new probe that gives different results, what happens about 'pass' 
decisions made using the old probes? You wouldn't want to make problems 
for the customers, would you? Many of the outline testing networks in 
CISPR 16-1 are 'hands-off' because of this, even though some are very 
vintage indeed.


John Woodgate OOO-Own Opinions Only
J M Woodgate and Associates www.woodjohn.uk
Rayleigh, Essex UK

On 2018-03-07 14:52, Patrick wrote:

Hello Ed -
Great story- thanks for sharing!

Just last year, we had a broken sensor head on a HI-6053.
It was built circa 2015, so it would be considered a "modern" probe.
I did the same as you and took it apart - it was already broken, so 
nothing to lose!

(how many of us have been doing that since we were kids!)

The description you give of the "old" probe matches exactly what I 
found inside the HI6053.

Dimensions were a bit different, and electronics are in a square box.
But the basic design of sensor and high impedance connecting cables 
are the same!

I guess some designs are robust enough to survive for decades.

Thanks again for the story.

BTW- thanks also for yesterday's story about the evolution of our 
industry.
It reminds me that what we think is "settled" is really just the 
boundary of our understanding.

And, as our understanding grows then those boundaries move too.

Always great to hear your perspective!
Thank you !

On Tue, Mar 6, 2018 at 2:57 PM, Edward Price <e...@jwjelp.com 
<mailto:e...@jwjelp.com>> wrote:


*Patrick:*

**

*The probe manufacturer says something like “keep the probe box
away or out of the field” or “best results are obtained with the
probe placed on a slant.” But then they show us isotropicity data
that promises +/- ¼ dB. It seems like those are contradictory
statements.*

*Back around 2002, I decided to dissect a dead Narda 8762(?) probe
which a customer helped me drop. The Narda was a white Fiberglas,
300 MHz to 1 GHz probe that looked like a very elegant German
“potato masher” hand grenade equipped with a cable that plugged
into an IFI EFS field sensor. I wish I had taken some good
pictures of the project, as few people venture that deep into such
expensive territory.*

*The head contained the orthogonal three-dipole array, with the
conductive arms looking like gold foil on a thin Fiberglass
substrate. The length of each dipole was about 1.5 inches. The
sensing elements might have been thermocouples, thermistors or
diodes, and they were mounted in the dipoles. Each sensor was also
connected to a pair of very high resistance plastic wires
(possibly doped with carbon like automotive spark plug wires) that
ran to the far end of the stalk where an analog signal
conditioning amplifier summed the three channels and provided a DC
output proportional to field strength. I was struck by the
delicacy of the sensor head, looking at what must have been a very
labor intensive assembly.*

*BTW, the signal conditioning amplifier was enclosed in a ¾”
diameter by 4” long section of tubular steel, so it was obvious
that this conductive mass (not to mention the shielded,
multi-conductor power & signal cable) would distort the measured
field and degrade the isotropicity.*

**

*/Ed Price
/**WB6WSN**/
/**Chula Vista, CA USA**//*

**

*From:*Patrick [mailto:conwa...@gmail.com
<mailto:conwa...@gmail.com>]
*Sent:* Tuesday, March 06, 2018 7:37 AM
    *To:* Edward Price
*Subject:* Re: [PSES] Field probe calibration

Hello Ed -

  Good morning!

  You are correct - the factors stored in the probe correct for
the non-linearities of the diode detector.

      (  as a side note- hearing a presentation live, and
asking/answering questions, is always more educational than a
sterile slide deck.

      i wish we all could sit through this presentation, ask
questions, and have dialog. )

Did you notice the warnings about errors possible in the
calibration process?

For instance, the "probe on a stick" is calibrated at an angle???

And for that probe they say the electronics box should be kept out
of the field???

   I understand the reasons, but keeping the box out of the field
is nearly impossible for most of our semi-anechoic chamber
applications!!

   And I rarely see them used at the same angle as calibrated.

  How does one quantify those effects?

  (...a topic for another thread ?)

But, getting back to the frequency response question...

Here is what I recall-

... As shown in the slides, the detector is connected across a
small (tiny?) dipole.

     the size of the dipole has some real-world limits.

     large enough to capture enough power to make a measuremen

Re: [PSES] Field probe calibration

[Patrick]

Hello Ed -
Great story- thanks for sharing!

Just last year, we had a broken sensor head on a HI-6053.
It was built circa 2015, so it would be considered a "modern" probe.
I did the same as you and took it apart - it was already broken, so nothing
to lose!
(how many of us have been doing that since we were kids!)

The description you give of the "old" probe matches exactly what I found
inside the HI6053.
Dimensions were a bit different, and electronics are in a square box.
But the basic design of sensor and high impedance connecting cables are the
same!
I guess some designs are robust enough to survive for decades.

Thanks again for the story.

BTW- thanks also for yesterday's story about the evolution of our industry.
It reminds me that what we think is "settled" is really just the boundary
of our understanding.
And, as our understanding grows then those boundaries move too.

Always great to hear your perspective!
Thank you !

On Tue, Mar 6, 2018 at 2:57 PM, Edward Price <e...@jwjelp.com> wrote:

> *Patrick:*
>
>
>
> *The probe manufacturer says something like “keep the probe box away or
> out of the field” or “best results are obtained with the probe placed on a
> slant.” But then they show us isotropicity data that promises +/- ¼ dB. It
> seems like those are contradictory statements.*
>
> *Back around 2002, I decided to dissect a dead Narda 8762(?) probe which a
> customer helped me drop. The Narda was a white Fiberglas, 300 MHz to 1 GHz
> probe that looked like a very elegant German “potato masher” hand grenade
> equipped with a cable that plugged into an IFI EFS field sensor. I wish I
> had taken some good pictures of the project, as few people venture that
> deep into such expensive territory.*
>
> *The head contained the orthogonal three-dipole array, with the conductive
> arms looking like gold foil on a thin Fiberglass substrate. The length of
> each dipole was about 1.5 inches. The sensing elements might have been
> thermocouples, thermistors or diodes, and they were mounted in the dipoles.
> Each sensor was also connected to a pair of very high resistance plastic
> wires (possibly doped with carbon like automotive spark plug wires) that
> ran to the far end of the stalk where an analog signal conditioning
> amplifier summed the three channels and provided a DC output proportional
> to field strength. I was struck by the delicacy of the sensor head, looking
> at what must have been a very labor intensive assembly.*
>
> *BTW, the signal conditioning amplifier was enclosed in a ¾” diameter by
> 4” long section of tubular steel, so it was obvious that this conductive
> mass (not to mention the shielded, multi-conductor power & signal cable)
> would distort the measured field and degrade the isotropicity.*
>
>
>
>
> *Ed Price **WB6WSN*
> *Chula Vista, CA USA*
>
>
>
> *From:* Patrick [mailto:conwa...@gmail.com]
> *Sent:* Tuesday, March 06, 2018 7:37 AM
> *To:* Edward Price
> *Subject:* Re: [PSES] Field probe calibration
>
>
>
> Hello Ed -
>
>   Good morning!
>
>
>
>   You are correct - the factors stored in the probe correct for the
> non-linearities of the diode detector.
>
>   (  as a side note- hearing a presentation live, and asking/answering
> questions, is always more educational than a sterile slide deck.
>
>   i wish we all could sit through this presentation, ask questions,
> and have dialog. )
>
>
>
> Did you notice the warnings about errors possible in the calibration
> process?
>
> For instance, the "probe on a stick" is calibrated at an angle???
>
> And for that probe they say the electronics box should be kept out of the
> field???
>
>I understand the reasons, but keeping the box out of the field is
> nearly impossible for most of our semi-anechoic chamber applications!!
>
>And I rarely see them used at the same angle as calibrated.
>
>   How does one quantify those effects?
>
>   (...a topic for another thread ?)
>
>
>
> But, getting back to the frequency response question...
>
> Here is what I recall-
>
> ... As shown in the slides, the detector is connected across a small
> (tiny?) dipole.
>
>  the size of the dipole has some real-world limits.
>
>  large enough to capture enough power to make a measurement possible.
>
>  small enough to minimize disturbance in the field.
>
>  the three orthogonal dipoles have to be close enough to represent the
> same physical space.
>
>  So the size, placement and response is a compromise away from "ideal"
> (i.e. not flat ).
>
>
>
> ... IMHO, there is nothing rev

Re: [PSES] Field probe calibration

[Ken Javor]

Note that 1.5² is just over a tenth wavelength at 1 GHz.  12.7%, to be
exact, and of course Ed was going from memory here.  We expect no resonances
with this dipole loaded at a high, capacitive impedance, or if we measure
its current output into a low impedance (allowing the short dipole to look
like a current source).

No doubt there are non-idealities, as Ed describes, but they are going to be
very much site-dependent: the answer you get depending on how the probe is
used, which is not something that can be corrected for in a lookup table.

Ken Javor
Phone: (256) 650-5261




From: Edward Price <e...@jwjelp.com>
Reply-To: Edward Price <e...@jwjelp.com>
Date: Tue, 6 Mar 2018 21:57:28 +
To: <EMC-PSTC@LISTSERV.IEEE.ORG>
Conversation: [PSES] Field probe calibration
Subject: Re: [PSES] Field probe calibration

Patrick:
 
The probe manufacturer says something like ³keep the probe box away or out
of the field² or ³best results are obtained with the probe placed on a
slant.² But then they show us isotropicity data that promises +/- 1Ž4 dB. It
seems like those are contradictory statements.
Back around 2002, I decided to dissect a dead Narda 8762(?) probe which a
customer helped me drop. The Narda was a white Fiberglas, 300 MHz to 1 GHz
probe that looked like a very elegant German ³potato masher² hand grenade
equipped with a cable that plugged into an IFI EFS field sensor. I wish I
had taken some good pictures of the project, as few people venture that deep
into such expensive territory.
The head contained the orthogonal three-dipole array, with the conductive
arms looking like gold foil on a thin Fiberglass substrate. The length of
each dipole was about 1.5 inches. The sensing elements might have been
thermocouples, thermistors or diodes, and they were mounted in the dipoles.
Each sensor was also connected to a pair of very high resistance plastic
wires (possibly doped with carbon like automotive spark plug wires) that ran
to the far end of the stalk where an analog signal conditioning amplifier
summed the three channels and provided a DC output proportional to field
strength. I was struck by the delicacy of the sensor head, looking at what
must have been a very labor intensive assembly.
BTW, the signal conditioning amplifier was enclosed in a 3Ž4² diameter by 4²
long section of tubular steel, so it was obvious that this conductive mass
(not to mention the shielded, multi-conductor power & signal cable) would
distort the measured field and degrade the isotropicity.
 
Ed Price
WB6WSN
Chula Vista, CA USA
 
From: Patrick [mailto:conwa...@gmail.com]
Sent: Tuesday, March 06, 2018 7:37 AM
To: Edward Price
Subject: Re: [PSES] Field probe calibration
 

Hello Ed - 

  Good morning!

 

  You are correct - the factors stored in the probe correct for the
non-linearities of the diode detector.

  (  as a side note- hearing a presentation live, and asking/answering
questions, is always more educational than a sterile slide deck.

  i wish we all could sit through this presentation, ask questions, and
have dialog. )

 

Did you notice the warnings about errors possible in the calibration
process?

For instance, the "probe on a stick" is calibrated at an angle???

And for that probe they say the electronics box should be kept out of the
field???

   I understand the reasons, but keeping the box out of the field is nearly
impossible for most of our semi-anechoic chamber applications!!

   And I rarely see them used at the same angle as calibrated.

  How does one quantify those effects?

  (...a topic for another thread ?)

 

But, getting back to the frequency response question...

Here is what I recall-

... As shown in the slides, the detector is connected across a small (tiny?)
dipole.  

 the size of the dipole has some real-world limits.

 large enough to capture enough power to make a measurement possible.

 small enough to minimize disturbance in the field.

 the three orthogonal dipoles have to be close enough to represent the
same physical space.

 So the size, placement and response is a compromise away from "ideal"
(i.e. not flat ).

 

... IMHO, there is nothing revolutionary in that information.

But, maybe I missed something?

Let me know your thoughts.

 

I would encourage local chapters to contact ETS, and ask them if they could
present at the local chapter meeting.

(DISCLAIMER - I have no affiliation with ETS, I just like the idea of
learning something new about something that was thought to be settled...)

 
-


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discussion list. To post a message to the list, send your e-mail to
<emc-p...@ieee.org>

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Attachments are not permitted but the IEEE PSES Online Communities site at
ht

Re: [PSES] Field probe calibration

[Edward Price]

Patrick:

The probe manufacturer says something like “keep the probe box away or out of 
the field” or “best results are obtained with the probe placed on a slant.” But 
then they show us isotropicity data that promises +/- ¼ dB. It seems like those 
are contradictory statements.
Back around 2002, I decided to dissect a dead Narda 8762(?) probe which a 
customer helped me drop. The Narda was a white Fiberglas, 300 MHz to 1 GHz 
probe that looked like a very elegant German “potato masher” hand grenade 
equipped with a cable that plugged into an IFI EFS field sensor. I wish I had 
taken some good pictures of the project, as few people venture that deep into 
such expensive territory.
The head contained the orthogonal three-dipole array, with the conductive arms 
looking like gold foil on a thin Fiberglass substrate. The length of each 
dipole was about 1.5 inches. The sensing elements might have been 
thermocouples, thermistors or diodes, and they were mounted in the dipoles. 
Each sensor was also connected to a pair of very high resistance plastic wires 
(possibly doped with carbon like automotive spark plug wires) that ran to the 
far end of the stalk where an analog signal conditioning amplifier summed the 
three channels and provided a DC output proportional to field strength. I was 
struck by the delicacy of the sensor head, looking at what must have been a 
very labor intensive assembly.
BTW, the signal conditioning amplifier was enclosed in a ¾” diameter by 4” long 
section of tubular steel, so it was obvious that this conductive mass (not to 
mention the shielded, multi-conductor power & signal cable) would distort the 
measured field and degrade the isotropicity.

Ed Price
WB6WSN
Chula Vista, CA USA

From: Patrick [mailto:conwa...@gmail.com]
Sent: Tuesday, March 06, 2018 7:37 AM
To: Edward Price
Subject: Re: [PSES] Field probe calibration

Hello Ed -
  Good morning!

  You are correct - the factors stored in the probe correct for the 
non-linearities of the diode detector.
  (  as a side note- hearing a presentation live, and asking/answering 
questions, is always more educational than a sterile slide deck.
  i wish we all could sit through this presentation, ask questions, and 
have dialog. )

Did you notice the warnings about errors possible in the calibration process?
For instance, the "probe on a stick" is calibrated at an angle???
And for that probe they say the electronics box should be kept out of the 
field???
   I understand the reasons, but keeping the box out of the field is nearly 
impossible for most of our semi-anechoic chamber applications!!
   And I rarely see them used at the same angle as calibrated.
  How does one quantify those effects?
  (...a topic for another thread ?)

But, getting back to the frequency response question...
Here is what I recall-
... As shown in the slides, the detector is connected across a small (tiny?) 
dipole.
 the size of the dipole has some real-world limits.
 large enough to capture enough power to make a measurement possible.
 small enough to minimize disturbance in the field.
 the three orthogonal dipoles have to be close enough to represent the same 
physical space.
 So the size, placement and response is a compromise away from "ideal" 
(i.e. not flat ).

... IMHO, there is nothing revolutionary in that information.
But, maybe I missed something?
Let me know your thoughts.

I would encourage local chapters to contact ETS, and ask them if they could 
present at the local chapter meeting.
(DISCLAIMER - I have no affiliation with ETS, I just like the idea of learning 
something new about something that was thought to be settled...)


-

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discussion list. To post a message to the list, send your e-mail to 
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Re: [PSES] Field probe calibration

[Edward Price]

Ken:

Yes, you are right, the probe doesn't know the frequency. Thus, the 
manufacturer has to make it flat, by design and construction, or you have to 
generate your own correction factors based on performance testing of the probe.

Ed Price
WB6WSN
Chula Vista, CA USA

From: Ken Javor [mailto:ken.ja...@emccompliance.com]
Sent: Monday, March 05, 2018 8:19 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Field probe calibration

It is clear that any correction table built into the field probe 
hardware/firmware/software is time domain only, so linearity correction factors 
based on amplitude, not frequency domain, because there is no frequency 
information unless you are looking at an entirely different kind of device 
designed to drive a spectrum analyzer.  With that sort of system (suppliers of 
which I am aware include Rohde & Schwarz and Narda), it is possible to correct 
in in the frequency domain, but again not a single standard out there is based 
on the use of such, as they are quite recent developments.

Ken Javor
Phone: (256) 650-5261


-

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Re: [PSES] Field probe calibration

[Ken Javor]

It is clear that any correction table built into the field probe
hardware/firmware/software is time domain only, so linearity correction
factors based on amplitude, not frequency domain, because there is no
frequency information unless you are looking at an entirely different kind
of device designed to drive a spectrum analyzer.  With that sort of system
(suppliers of which I am aware include Rohde & Schwarz and Narda), it is
possible to correct in in the frequency domain, but again not a single
standard out there is based on the use of such, as they are quite recent
developments.

Ken Javor
Phone: (256) 650-5261



From: Edward Price <e...@jwjelp.com>
Reply-To: Edward Price <e...@jwjelp.com>
Date: Tue, 6 Mar 2018 01:27:07 +
To: <EMC-PSTC@LISTSERV.IEEE.ORG>
Conversation: [PSES] Field probe calibration
Subject: Re: [PSES] Field probe calibration

This is interesting, as Mr. Chen stated in ³Practical Considerations on EMC
Measurements using Field Probes² that:
 
³Modern probes have correction table built into the probe. Microcontrollers
inside the probes apply linearity correction. As a result, probe reading
reflects the true field value for CW signals. A user need not to correct for
this manually.²
 
http://ieee.rackoneup.net/rrvs/10/Zhong%20Probe.pdf
 
I believe Mr. Chen was referring to the Lindgren HI-6005 probe in this
example. It wasn¹t clear to me if he meant that the probe had an internal
correction table for the frequency domain, the amplitude domain or both.
 
I would think that isotropicity would have to be proven, not claimed,
through actual measurements at time of calibration. These probes are
operating at frequencies where even a block of Delrin can distort an
E-field. In that document, Mr. Chen presents data for the HI-6005 which
shows a +/- 1Ž4 dB variation in isotropicity (at 400 MHz & 1 GHz, but what
about 6 GHz); that¹s very impressive. I wonder if the probe¹s internal
microprocessor applies any correction factor to smooth the isotropicity?
 
The amplitude and frequency linearity must also be measured, because even
tiny variations in construction of the probes and electronics can cause
resonances or couplings.
 
·   There once was a time when we just measured whatever came out of the
manufacturer¹s antenna.

·   Then we believed that all of the manufacturer¹s antennas had the
same factory response.

·   Then we required calibration data for each antenna.

·   Then we realized that antennas can change, so periodic calibration
became a must.

·   And then we realized that calibrations needed to be done
³end-to-end² starting with a uniform applied RF field.

·   And now we realize that ³several points per octave² is not good
enough resolution.

·   And now that we have microprocessors plucking fudge factors off an
inaccessible table, we have yet another layer on this data onion, and we
have to know what it does to our raw data.

 
Ed Price
WB6WSN
Chula Vista, CA USA
 
From: Patrick [mailto:conwa...@gmail.com]
Sent: Monday, March 05, 2018 1:36 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Field probe calibration
 

A great presentation on field probes can be found on the web.

The author is Zhong Chen, an engineer with one of the probe manufacturers.

I was lucky enough last year to be in the audience for a live presentation
of this at our local EMC Chapter.

 

I found it by searching:  "ets lindgren e field probe theory"

 

It states, among other things, that frequency response correction is applied
during end use!

 

Unfortunately, it doesn't state the amount of correction needed, nor the
frequency resolution needed (doh!).

But, it does answer questions on whether modern probes are frequency
dependent devices.

 

It is an interesting presentation, and I highly recommend it for anyone that
wants to learn more about their test equipment.

 

 
-


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discussion list. To post a message to the list, send your e-mail to
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well-used formats), large files, etc.

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-

This message is from the IE

Re: [PSES] Field probe calibration

[Edward Price]

This is interesting, as Mr. Chen stated in “Practical Considerations on EMC 
Measurements using Field Probes” that:

“Modern probes have correction table built into the probe. Microcontrollers 
inside the probes apply linearity correction. As a result, probe reading 
reflects the true field value for CW signals. A user need not to correct for 
this manually.”

http://ieee.rackoneup.net/rrvs/10/Zhong%20Probe.pdf

I believe Mr. Chen was referring to the Lindgren HI-6005 probe in this example. 
It wasn’t clear to me if he meant that the probe had an internal correction 
table for the frequency domain, the amplitude domain or both.

I would think that isotropicity would have to be proven, not claimed, through 
actual measurements at time of calibration. These probes are operating at 
frequencies where even a block of Delrin can distort an E-field. In that 
document, Mr. Chen presents data for the HI-6005 which shows a +/- ¼ dB 
variation in isotropicity (at 400 MHz & 1 GHz, but what about 6 GHz); that’s 
very impressive. I wonder if the probe’s internal microprocessor applies any 
correction factor to smooth the isotropicity?

The amplitude and frequency linearity must also be measured, because even tiny 
variations in construction of the probes and electronics can cause resonances 
or couplings.


·There once was a time when we just measured whatever came out of the 
manufacturer’s antenna.

·Then we believed that all of the manufacturer’s antennas had the same 
factory response.

·Then we required calibration data for each antenna.

·Then we realized that antennas can change, so periodic calibration 
became a must.

·And then we realized that calibrations needed to be done “end-to-end” 
starting with a uniform applied RF field.

·And now we realize that “several points per octave” is not good enough 
resolution.

·And now that we have microprocessors plucking fudge factors off an 
inaccessible table, we have yet another layer on this data onion, and we have 
to know what it does to our raw data.

Ed Price
WB6WSN
Chula Vista, CA USA

From: Patrick [mailto:conwa...@gmail.com]
Sent: Monday, March 05, 2018 1:36 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Field probe calibration

A great presentation on field probes can be found on the web.
The author is Zhong Chen, an engineer with one of the probe manufacturers.
I was lucky enough last year to be in the audience for a live presentation of 
this at our local EMC Chapter.

I found it by searching:  "ets lindgren e field probe theory"

It states, among other things, that frequency response correction is applied 
during end use!

Unfortunately, it doesn't state the amount of correction needed, nor the 
frequency resolution needed (doh!).
But, it does answer questions on whether modern probes are frequency dependent 
devices.

It is an interesting presentation, and I highly recommend it for anyone that 
wants to learn more about their test equipment.



-

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-p...@ieee.org>

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 
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Re: [PSES] Field probe calibration

[Ken Javor]

Thanks for the slide package but have to disagree. The last few slides are
about frequency effects due to probe placement, not inherent in the probe
itself. There is no way to correct for effects due to probe placement. The
frequency correction they talk about in the last slide is how linearity is
affected vs. frequency and that is a very minor correction.  And note this
final phrase:

³Frequency response correction is applied during end use.²

That means it has to be done outside the probe electronics, because the
probe electronics doesn¹t know what the frequency is.  Not saying you can¹t
do this, just it isn¹t required and was never envisioned in any of these
standards, and the degree of the error is so much smaller than other error
sources that it isn¹t worth it.

I am not familiar with modern EMI software control packages. Do any of them
make proviso for this?

Ken Javor
Phone: (256) 650-5261



From: Patrick <conwa...@gmail.com>
Date: Mon, 5 Mar 2018 15:26:03 -0700
To: Ken Javor <ken.ja...@emccompliance.com>
Cc: <EMC-PSTC@listserv.ieee.org>
Subject: Re: [PSES] Field probe calibration

http://ieee.rackoneup.net/rrvs/10/Zhong%20Probe.pdf

Look at the last slide, the last bullet.

The detail analysis can be found within the slides themselves, but that last
bullet summarizes the point.

On Mon, Mar 5, 2018 at 3:10 PM, Ken Javor <ken.ja...@emccompliance.com>
wrote:
> Didn¹t find cited article but did find published ETS/Lindgren specs on a
> laser-powered sensor, showing frequency-dependent performance well within +/-
> 1 dB tolerance over entire specified frequency range below 1 GHz.  Also, no
> standard out there requires the level-of-effort to post-process the field
> sensor electronics unit output on a frequency-by-frequency basis.
> 
> 
> http://www.ets-lindgren.com/sites/etsauthor/ProductsManuals/Probes_Monitors/EM
> C%20Field%20Probes%20399395%20A.pdf
> 
> Page 55.
> 
> Also found:  ³Practical Considerations for Radiated Immunities Measurement
> using ETS-Lindgren EMC Probes,² with nothing about frequency dependence
> corrections.
> 
> Ken Javor
> Phone: (256) 650-5261 <tel:(256)%20650-5261>
> 
> 
> 
> 
> From: Patrick <conwa...@gmail.com>
> Date: Mon, 5 Mar 2018 14:36:11 -0700
> To: Ken Javor <ken.ja...@emccompliance.com>
> Cc: <EMC-PSTC@listserv.ieee.org>
> Subject: Re: [PSES] Field probe calibration
> 
> A great presentation on field probes can be found on the web.
> The author is Zhong Chen, an engineer with one of the probe manufacturers. 
> I was lucky enough last year to be in the audience for a live presentation of
> this at our local EMC Chapter.
> 
> I found it by searching:  "ets lindgren e field probe theory"  
> 
> It states, among other things, that frequency response correction is applied
> during end use!
> 
> Unfortunately, it doesn't state the amount of correction needed, nor the
> frequency resolution needed (doh!).
> But, it does answer questions on whether modern probes are frequency dependent
> devices.
> 
> It is an interesting presentation, and I highly recommend it for anyone that
> wants to learn more about their test equipment.
> 
> 
> On Mon, Mar 5, 2018 at 1:08 PM, Ken Javor <ken.ja...@emccompliance.com> wrote:
>> In turn:
>> 
>> Everyone does not know that MIL-STD-461 requires RS103 pre-test
>> verification.  I don¹t.  Please explain further.
>> 
>> RTCA/DO-160 requires pre-calibration of the field in a manner similar to that
>> in the exercise that started this thread. Note at one point only, so that the
>> point about field variations down the length of the test set-up as for RS103
>> also applies here.
>> 
>> My use of the 61000-4-3 example was a pedagogical tool to illustrate that the
>> OP test results looked good relative to a very stringent industry standard.
>> 
>> When you ask whether some tolerance is insignificant, that begs the question
>> as to what is the required tolerance.  In MIL-STD-461, the effect of the
>> ground plane and immediate vicinity of the test sample and the lack of good
>> quality absorption below around 80 MHz are way bigger factors than
>> non-idealities in probe calibration.   MIL-STD-461 requires only one probe
>> (more are allowed) so that even if the field intensity is within the correct
>> tolerance at that point, there is no control over what the fields are down
>> the length and breadth of the test set-up.  And MIL-STD-461 allows for 3 dB
>> variation in instrumentation tolerances, so there you go on your field
>> probes.
>> 
>> And I don¹t know what all sorts of control software is envisioned out there,
>> but an off-the-shelf field probe and control-display unit at lea

Re: [PSES] Field probe calibration

[Patrick]

http://ieee.rackoneup.net/rrvs/10/Zhong%20Probe.pdf

Look at the last slide, the last bullet.

The detail analysis can be found within the slides themselves, but that
last bullet summarizes the point.

On Mon, Mar 5, 2018 at 3:10 PM, Ken Javor <ken.ja...@emccompliance.com>
wrote:

> Didn’t find cited article but did find published ETS/Lindgren specs on a
> laser-powered sensor, showing frequency-dependent performance well within
> +/- 1 dB tolerance over entire specified frequency range below 1 GHz.
> Also, no standard out there requires the level-of-effort to post-process
> the field sensor electronics unit output on a frequency-by-frequency basis.
>
>
> http://www.ets-lindgren.com/sites/etsauthor/ProductsManuals/Probes_
> Monitors/EMC%20Field%20Probes%20399395%20A.pdf
>
> Page 55.
>
> Also found:  “Practical Considerations for Radiated Immunities Measurement
> using ETS-Lindgren EMC Probes,” with nothing about frequency dependence
> corrections.
>
> Ken Javor
> Phone: (256) 650-5261
>
>
>
> --
> *From: *Patrick <conwa...@gmail.com>
> *Date: *Mon, 5 Mar 2018 14:36:11 -0700
> *To: *Ken Javor <ken.ja...@emccompliance.com>
> *Cc: *<EMC-PSTC@listserv.ieee.org>
> *Subject: *Re: [PSES] Field probe calibration
>
> A great presentation on field probes can be found on the web.
> The author is Zhong Chen, an engineer with one of the probe manufacturers.
> I was lucky enough last year to be in the audience for a live presentation
> of this at our local EMC Chapter.
>
> I found it by searching:  "ets lindgren e field probe theory"
>
> It states, among other things, that frequency response correction is
> applied during end use!
>
> Unfortunately, it doesn't state the amount of correction needed, nor the
> frequency resolution needed (doh!).
> But, it does answer questions on whether modern probes are frequency
> dependent devices.
>
> It is an interesting presentation, and I highly recommend it for anyone
> that wants to learn more about their test equipment.
>
>
> On Mon, Mar 5, 2018 at 1:08 PM, Ken Javor <ken.ja...@emccompliance.com>
> wrote:
>
> In turn:
>
> Everyone does not know that MIL-STD-461 requires RS103 pre-test
> verification.  I don’t.  Please explain further.
>
> RTCA/DO-160 requires pre-calibration of the field in a manner similar to
> that in the exercise that started this thread. Note at one point only, so
> that the point about field variations down the length of the test set-up as
> for RS103 also applies here.
>
> My use of the 61000-4-3 example was a pedagogical tool to illustrate that
> the OP test results looked good relative to a very stringent industry
> standard.
>
> When you ask whether some tolerance is insignificant, that begs the
> question as to what is the required tolerance.  In MIL-STD-461, the effect
> of the ground plane and immediate vicinity of the test sample and the lack
> of good quality absorption below around 80 MHz are way bigger factors than
> non-idealities in probe calibration.   MIL-STD-461 requires only one probe
> (more are allowed) so that even if the field intensity is within the
> correct tolerance at that point, there is no control over what the fields
> are down the length and breadth of the test set-up.  And MIL-STD-461 allows
> for 3 dB variation in instrumentation tolerances, so there you go on your
> field probes.
>
> And I don’t know what all sorts of control software is envisioned out
> there, but an off-the-shelf field probe and control-display unit at least
> at the time when RS103 was written (1989-1993) was not a frequency
> sensitive device. The unit reported a field intensity only. The frequency
> information came from the transmit side.  Leveling was performed on the
> field intensity reported by the probe electronics unit.  There was no
> correction envisioned for probe factors at each tuned frequency.  Not
> saying that couldn’t be done in a controller external to the probe
> electronics given detailed probe calibration info, just that wasn’t part of
> the plan back in the day. I would be interested to hear from readers as to
> whether that is now common.
>
> As Mr. Woodgate notes and I affirm, a 20% variation in probe calibration
> is way down in the noise even in a 61000-4-3 UFA calibration, not to
> mention the OP set-up with probes 10 cm over a ground plane, which to my
> knowledge is never the requirement.
>
> Which all leads up to an answer to this question:
>
> “Would you agree, as an engineer, its always better to have the data, then
> to operate in the blind?”
>
> The answer is, “Not only no, but hell no, if I know beforehand that the
> numbers don’t matter.”
>
>
> Ken 

Re: [PSES] Field probe calibration

[Patrick]

A great presentation on field probes can be found on the web.
The author is Zhong Chen, an engineer with one of the probe manufacturers.
I was lucky enough last year to be in the audience for a live presentation
of this at our local EMC Chapter.

I found it by searching:  "ets lindgren e field probe theory"

It states, among other things, that frequency response correction is
applied during end use!

Unfortunately, it doesn't state the amount of correction needed, nor the
frequency resolution needed (doh!).
But, it does answer questions on whether modern probes are frequency
dependent devices.

It is an interesting presentation, and I highly recommend it for anyone
that wants to learn more about their test equipment.


On Mon, Mar 5, 2018 at 1:08 PM, Ken Javor <ken.ja...@emccompliance.com>
wrote:

> In turn:
>
> Everyone does not know that MIL-STD-461 requires RS103 pre-test
> verification.  I don’t.  Please explain further.
>
> RTCA/DO-160 requires pre-calibration of the field in a manner similar to
> that in the exercise that started this thread. Note at one point only, so
> that the point about field variations down the length of the test set-up as
> for RS103 also applies here.
>
> My use of the 61000-4-3 example was a pedagogical tool to illustrate that
> the OP test results looked good relative to a very stringent industry
> standard.
>
> When you ask whether some tolerance is insignificant, that begs the
> question as to what is the required tolerance.  In MIL-STD-461, the effect
> of the ground plane and immediate vicinity of the test sample and the lack
> of good quality absorption below around 80 MHz are way bigger factors than
> non-idealities in probe calibration.   MIL-STD-461 requires only one probe
> (more are allowed) so that even if the field intensity is within the
> correct tolerance at that point, there is no control over what the fields
> are down the length and breadth of the test set-up.  And MIL-STD-461 allows
> for 3 dB variation in instrumentation tolerances, so there you go on your
> field probes.
>
> And I don’t know what all sorts of control software is envisioned out
> there, but an off-the-shelf field probe and control-display unit at least
> at the time when RS103 was written (1989-1993) was not a frequency
> sensitive device. The unit reported a field intensity only. The frequency
> information came from the transmit side.  Leveling was performed on the
> field intensity reported by the probe electronics unit.  There was no
> correction envisioned for probe factors at each tuned frequency.  Not
> saying that couldn’t be done in a controller external to the probe
> electronics given detailed probe calibration info, just that wasn’t part of
> the plan back in the day. I would be interested to hear from readers as to
> whether that is now common.
>
> As Mr. Woodgate notes and I affirm, a 20% variation in probe calibration
> is way down in the noise even in a 61000-4-3 UFA calibration, not to
> mention the OP set-up with probes 10 cm over a ground plane, which to my
> knowledge is never the requirement.
>
> Which all leads up to an answer to this question:
>
> “Would you agree, as an engineer, its always better to have the data, then
> to operate in the blind?”
>
> The answer is, “Not only no, but hell no, if I know beforehand that the
> numbers don’t matter.”
>
>
> Ken Javor
> Phone: (256) 650-5261
>
>
> ------
> *From: *Patrick <conwa...@gmail.com>
> *Date: *Mon, 5 Mar 2018 11:10:52 -0700
> *To: *Ken Javor <ken.ja...@emccompliance.com>
> *Cc: *<EMC-PSTC@listserv.ieee.org>
> *Subject: *Re: [PSES] Field probe calibration
>
> Well, some of us have to consider other requirements, not just EN's.
>
> What if the test is -461, or DO-160 ?
> And what if the requirement is 200 V/m ?
>
> As everyone knows, those require a pre-test verification, not a
> requirement for "uniform field"?
>
> So a 20% error gives anywhere from 160 V/m to 240 V/m.
> A 600 V/m target is anywhere from 480 V/m to 720 V/m.
>
> Is that insignificant?
> Maybe, maybe not.
> Depends on you and your customer.
>
> I recommend to always check a test labs calibration factors.
> If the factors don't show the resonances, then there are built in errors.
> An informed decision can be made whether to accept, or move to another lab.
>
> Would you agree, as an engineer, its always better to have the data, then
> to operate in the blind?
>
>
> On Mon, Mar 5, 2018 at 10:21 AM, Ken Javor <ken.ja...@emccompliance.com>
> wrote:
>
> I am totally with John Woodgate on this – 20% deltas are insignificant in
> the larger picture. I only used 61000-4-3 to demonstrate the fallacy of
> worryi

Re: [PSES] Field probe calibration

[Ken Javor]

In turn:

Everyone does not know that MIL-STD-461 requires RS103 pre-test
verification.  I don¹t.  Please explain further.

RTCA/DO-160 requires pre-calibration of the field in a manner similar to
that in the exercise that started this thread. Note at one point only, so
that the point about field variations down the length of the test set-up as
for RS103 also applies here.

My use of the 61000-4-3 example was a pedagogical tool to illustrate that
the OP test results looked good relative to a very stringent industry
standard.

When you ask whether some tolerance is insignificant, that begs the question
as to what is the required tolerance.  In MIL-STD-461, the effect of the
ground plane and immediate vicinity of the test sample and the lack of good
quality absorption below around 80 MHz are way bigger factors than
non-idealities in probe calibration.   MIL-STD-461 requires only one probe
(more are allowed) so that even if the field intensity is within the correct
tolerance at that point, there is no control over what the fields are down
the length and breadth of the test set-up.  And MIL-STD-461 allows for 3 dB
variation in instrumentation tolerances, so there you go on your field
probes.

And I don¹t know what all sorts of control software is envisioned out there,
but an off-the-shelf field probe and control-display unit at least at the
time when RS103 was written (1989-1993) was not a frequency sensitive
device. The unit reported a field intensity only. The frequency information
came from the transmit side.  Leveling was performed on the field intensity
reported by the probe electronics unit.  There was no correction envisioned
for probe factors at each tuned frequency.  Not saying that couldn¹t be done
in a controller external to the probe electronics given detailed probe
calibration info, just that wasn¹t part of the plan back in the day. I would
be interested to hear from readers as to whether that is now common.

As Mr. Woodgate notes and I affirm, a 20% variation in probe calibration is
way down in the noise even in a 61000-4-3 UFA calibration, not to mention
the OP set-up with probes 10 cm over a ground plane, which to my knowledge
is never the requirement.

Which all leads up to an answer to this question:

³Would you agree, as an engineer, its always better to have the data, then
to operate in the blind?²

The answer is, ³Not only no, but hell no, if I know beforehand that the
numbers don¹t matter.²


Ken Javor
Phone: (256) 650-5261



From: Patrick <conwa...@gmail.com>
Date: Mon, 5 Mar 2018 11:10:52 -0700
To: Ken Javor <ken.ja...@emccompliance.com>
Cc: <EMC-PSTC@listserv.ieee.org>
Subject: Re: [PSES] Field probe calibration

Well, some of us have to consider other requirements, not just EN's.
  
What if the test is -461, or DO-160 ?
And what if the requirement is 200 V/m ?

As everyone knows, those require a pre-test verification, not a requirement
for "uniform field"?

So a 20% error gives anywhere from 160 V/m to 240 V/m.
A 600 V/m target is anywhere from 480 V/m to 720 V/m.

Is that insignificant?
Maybe, maybe not.
Depends on you and your customer.

I recommend to always check a test labs calibration factors.
If the factors don't show the resonances, then there are built in errors.
An informed decision can be made whether to accept, or move to another lab.

Would you agree, as an engineer, its always better to have the data, then to
operate in the blind?


On Mon, Mar 5, 2018 at 10:21 AM, Ken Javor <ken.ja...@emccompliance.com>
wrote:
> I am totally with John Woodgate on this ­ 20% deltas are insignificant in the
> larger picture. I only used 61000-4-3 to demonstrate the fallacy of worrying
> about such small deviations when the overall requirement in a really
> well-designed and expensive chamber is +6, - 0 dB. Consider the type of
> absorber used, the limited frequency range (80 ­ 1000 MHz), the total lack of
> conducting material, and the fact that 25% of the UFA may be excluded from the
> 6 dB variation.  
> 
> Your variations are well within that tolerance, and your room and set-up
> nowhere near that good.  If you want better than what you have, you will need
> a chamber and set-up much better than that for 61000-4-3 ­ impractical, to say
> the least.
> 
> The point is, make sure you have enough amplifier to do the job with some
> margin. That¹s as good as you are going to get.
> 
> Ken Javor
> Phone: (256) 650-5261 <tel:(256)%20650-5261>
> 
> 
> 
> From: John Woodgate <j...@woodjohn.uk>
> Reply-To: John Woodgate <j...@woodjohn.uk>
> Date: Mon, 5 Mar 2018 16:19:10 +
> To: <EMC-PSTC@LISTSERV.IEEE.ORG>
> Subject: Re: [PSES] Field probe calibration
> 
>    
> 
> +/- 20% doesn't seem to be enough to explain the reported result. After all,
> assuming the +/- 20% is off the spectrum analyser, 1.2 is +1.6 dB and 0.8 is
> -1.9 dB. These ar

Re: [PSES] Field probe calibration

[John Woodgate]

traight on, why not do that? I can save that amplifier cost
- at least until I get a new probe. The calibrations don't
seem to mean that much based on my data, so with a composite
reading whichever probe orientation gives me the highest
field should be ok.

Also, any replies I make may be delayed. It seems like I
usually see a 4+ hour delay between when I email the
listserve, and when it is delivered.

Thanks,

David Schaefer


From: Ken Javor [mailto:ken.ja...@emccompliance.com
<mailto:ken.ja...@emccompliance.com>]
Sent: Sunday, March 04, 2018 12:17 PM
    To: EMC-PSTC@LISTSERV.IEEE.ORG
<mailto:EMC-PSTC@LISTSERV.IEEE.ORG>
Subject: Re: [PSES] Field probe calibration

In turn:

It is not surprising at all that it takes less power to
generate the vertical field than the horizontal field. 
That's the effect of the conducting ground plane. The OP
doesn't say what spec they are working to, but that is why
MIL-STD-461 below 1 GHz has the probe 30 cm above the ground
plane, to limit that effect.

Comments, such as Gert Gremmen's, that measurements in the
presence of a ground plane (or any conducting structure) are
useless, are themselves useless.  The comment reflects a
difference in standards of value.  If one is starving, food
is the most important priority. If one is asphyxiating,
oxygen is the primary need.  It is logically incorrect for
two people suffering these two conditions to point at each
other and say the other one is wrong about his priorities:
they are both correct within the scope of their individual
circumstances. The only logical observation that can be made
is that oxygen needs to be supplied sooner than food, if the
standard of value is immediate survival.

In the world of goods slated for use in home, office and
factory, the coin of the realm is accuracy and minimum
uncertainty, so that qualifications everywhere result in a
level economic playing field. Required field intensities
(1/3/10 V/m) are very low compared to the world of vehicle
EMI testing (as high as 200 V/m, sometimes beyond), so that
(again relative) low power amplifiers may be used with
antennas separated from the test area by three meters instead
of one, facilitating the calibration of a quiet zone in the
complete and utter absence of any conducting surfaces,
because the end-item use does not include installation on or
near a conducting ground plane.

This is all in sharp contrast to the qualification of
equipment slated for use on a metal or partially metallic
vehicle.  The ground plane is of material use in reducing the
intensity of the horizontal field near it, as noted in the OP
and taken advantage of by the very standards that deal with
such qualifications: the ground plane is our friend. Let us
count the ways:

As mentioned above, the ground plane reduces the intensity of
a horizontally polarized field in its immediate vicinity.

The presence of a ground plane causes cables in its vicinity
to react to fields not as an antenna as in the 61000-4-3 and
61000-4-6 paradigm, but as a transmission line. Transmission
lines radiate less per unit of current they carry, and couple
less power from an incident field, than do antennas. Given
the very stringent RE and RS requirements in vehicle
standards, we need all the help we can get.

And finally, metallic equipment enclosures bonded to a ground
plane allows filters to efficiently shunt incoming noise to
the ground plane and away from internal circuitry, and
perform that same function for noise currents coupled to
shields that terminate in a low impedance manner to the
exterior of such metallic equipment enclosures.

Now having dealt with Gert - his recurring comment about the
futility of vehicle EMI testing re ground planes consistently
eliciting the above response from me, ad infinitum and ad
nauseum, lets look at the OP provided test data, especially
in light of the 61000-4-3 required UFA (uniform field area)
uniformity requirement of +6 dB, -0 dB for 75% of the
required sixteen measurement points.

What I see is that for a given polarization and frequency
every single position measured is within 6 dB of the others. 
In the immediate presence of a ground plane, no less!  The
cup is not half full - the cornucopia is overflowing.  This
performance greatly exceeds the MIL-STD-461 requirement:
there is no requirement for multiple measurement po

Re: [PSES] Field probe calibration

[John Woodgate]

See below.

John Woodgate OOO-Own Opinions Only
J M Woodgate and Associates www.woodjohn.uk
Rayleigh, Essex UK

On 2018-03-05 18:10, Patrick wrote:

Well, some of us have to consider other requirements, not just EN's.

What if the test is -461, or DO-160 ?
And what if the requirement is 200 V/m ?

As everyone knows, those require a pre-test verification, not a 
requirement for "uniform field"?


So a 20% error gives anywhere from 160 V/m to 240 V/m.
JMW: Nevertheless, these are the same dB differences as I posted. If 
there is no better solution, increase the field strength until you are 
sure it is sufficient. There is no way your are going to finagle the 
laws of physics to get closely consistent results in near-field 
conditions. You can regard your reported results as 'additional 
calibration factors', applicable only to that exact set-up in which they 
were measured.

A 600 V/m target is anywhere from 480 V/m to 720 V/m.

Is that insignificant?
Maybe, maybe not.
Depends on you and your customer.
JMW: It's still a range of -1.9 dB to +1.6 dB. If 3.5 dB is crucial, the 
product is probably too near the limit for comfort, unless it's a one-off.


I recommend to always check a test labs calibration factors.
If the factors don't show the resonances, then there are built in errors.
An informed decision can be made whether to accept, or move to another 
lab.


Would you agree, as an engineer, its always better to have the data, 
then to operate in the blind?
JMW: Your minor typo makes that a very profound question. People do 
exactly that. They have the data but do not analyse its significance.

This thread is too long, so I have attenuated it.




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Re: [PSES] Field probe calibration

[Patrick]

Well, some of us have to consider other requirements, not just EN's.

What if the test is -461, or DO-160 ?
And what if the requirement is 200 V/m ?

As everyone knows, those require a pre-test verification, not a requirement
for "uniform field"?

So a 20% error gives anywhere from 160 V/m to 240 V/m.
A 600 V/m target is anywhere from 480 V/m to 720 V/m.

Is that insignificant?
Maybe, maybe not.
Depends on you and your customer.

I recommend to always check a test labs calibration factors.
If the factors don't show the resonances, then there are built in errors.
An informed decision can be made whether to accept, or move to another lab.

Would you agree, as an engineer, its always better to have the data, then
to operate in the blind?


On Mon, Mar 5, 2018 at 10:21 AM, Ken Javor <ken.ja...@emccompliance.com>
wrote:

> I am totally with John Woodgate on this – 20% deltas are insignificant in
> the larger picture. I only used 61000-4-3 to demonstrate the fallacy of
> worrying about such small deviations when the overall requirement in a
> really well-designed and expensive chamber is +6, - 0 dB. Consider the type
> of absorber used, the limited frequency range (80 – 1000 MHz), the total
> lack of conducting material, and the fact that 25% of the UFA may be
> excluded from the 6 dB variation.
>
> Your variations are well within that tolerance, and your room and set-up
> nowhere near that good.  If you want better than what you have, you will
> need a chamber and set-up much better than that for 61000-4-3 –
> impractical, to say the least.
>
> The point is, make sure you have enough amplifier to do the job with some
> margin. That’s as good as you are going to get.
>
> Ken Javor
> Phone: (256) 650-5261
>
>
> --
> *From: *John Woodgate <j...@woodjohn.uk>
> *Reply-To: *John Woodgate <j...@woodjohn.uk>
> *Date: *Mon, 5 Mar 2018 16:19:10 +
> *To: *<EMC-PSTC@LISTSERV.IEEE.ORG>
> *Subject: *Re: [PSES] Field probe calibration
>
>
>
> +/- 20% doesn't seem to be enough to explain the reported result. After
> all, assuming the +/- 20% is off the spectrum analyser, 1.2 is +1.6 dB and
> 0.8 is -1.9 dB. These are small, but not negligible. If the +/-20% relates
> to power, they are even smaller in dB, of course.
>
>
> John Woodgate OOO-Own Opinions Only
> J M Woodgate and Associates www.woodjohn.uk <http://www.woodjohn.uk>
> <http://www.woodjohn.uk>
> Rayleigh, Essex UK
>
> On 2018-03-05 15:57, Patrick wrote:
>
>
>
>
> Hi David -
>
>
>
> I had this same problem.
>
> I'm actually glad to see another engineer looking into this!
>
> The answer is not test setup,
>
>
> not ground plane,
>
> not distance to tabletop, etc.
>
>
> Each of those can be significant, and should be controlled, but...
>
>
>
>
>
>
>
>
> The problem you describe sounds exactly like one I had two years ago.
>
> If it is the same problem, the root cause is the *probe calibration*.
>
> The "normal" calibration data that every cal lab provides is too course.
>
> It hides (skips over) resonances in the probes.
>
> Only a finer calibration step size will resolve this problem.
>
>
>
>
>
>
>
> Here is my abbreviated story...
>
>
>
>
>
> I started with data just like yours.
>
> I had 6 probes: they were two model FP4000, and four of the HI6053.
>
>
>
>
> ...  amplifiers, chambers, height above table, orientation, etc>
>
>
>
>
> The root cause is the "normal" cal.
>
> It uses a course step size in frequency.
>
> When it is too course, it misses resonances in the probe.
>
> Those resonances are significant, as much as +/- 20% in my equipment.
>
>
>
>
> To prove this, I sent a probe out for "enhanced" cal.
>
> I requested both a "normal" cal and a higher resolution cal.
>
> I asked for 5% steps below 1 GHz and 100 MHz steps above 1 GHz.
>
>
>
>
> When the data came back I plotted the cal factors on top of each other.
>
> It was obvious.
>
> The course cal points of a "normal" calibration will hide resonances that
> are +/- 20% deviations.
>
>
> (above sentence should be BOLD, UNDERLINE, asterisks)
>
>
>
>
>
>
>
> My conclusion:  Any probe used for accredited test must have calibration
> data showing the resonances.
>
> If it doesn't, then the lab is guaranteed to be over-testing and
> under-testing.
>
>
>
>
> DM me and I'll be glad to discuss.
>
>
>
>
> Patrick
>
>
>
>
>
>
>
>
>
>
> On Sun, Mar 4, 2018 at 8:33 PM, Schaefer, David <ds

Re: [PSES] Field probe calibration

[Ken Javor]

I am totally with John Woodgate on this ­ 20% deltas are insignificant in
the larger picture. I only used 61000-4-3 to demonstrate the fallacy of
worrying about such small deviations when the overall requirement in a
really well-designed and expensive chamber is +6, - 0 dB. Consider the type
of absorber used, the limited frequency range (80 ­ 1000 MHz), the total
lack of conducting material, and the fact that 25% of the UFA may be
excluded from the 6 dB variation.

Your variations are well within that tolerance, and your room and set-up
nowhere near that good.  If you want better than what you have, you will
need a chamber and set-up much better than that for 61000-4-3 ­ impractical,
to say the least.

The point is, make sure you have enough amplifier to do the job with some
margin. That¹s as good as you are going to get.

Ken Javor
Phone: (256) 650-5261



From: John Woodgate <j...@woodjohn.uk>
Reply-To: John Woodgate <j...@woodjohn.uk>
Date: Mon, 5 Mar 2018 16:19:10 +
To: <EMC-PSTC@LISTSERV.IEEE.ORG>
Subject: Re: [PSES] Field probe calibration

   

+/- 20% doesn't seem to be enough to explain the reported result. After all,
assuming the +/- 20% is off the spectrum analyser, 1.2 is +1.6 dB and 0.8 is
-1.9 dB. These are small, but not negligible. If the +/-20% relates to
power, they are even smaller in dB, of course.
 
 
John Woodgate OOO-Own Opinions Only
J M Woodgate and Associates www.woodjohn.uk <http://www.woodjohn.uk>
Rayleigh, Essex UK
 
On 2018-03-05 15:57, Patrick wrote:
 
 
>  
> Hi David -  
> 
>  
>  
> I had this same problem.  
>  
> I'm actually glad to see another engineer looking into this!
>  
> The answer is not test setup,
>  
>  
>     not ground plane, 
>  
>     not distance to tabletop, etc.  
>  
>  
> Each of those can be significant, and should be controlled, but...
>  
>  
> 
>  
>  
> 
>  
>  
> The problem you describe sounds exactly like one I had two years ago.
>  
> If it is the same problem, the root cause is the *probe calibration*.
>  
> The "normal" calibration data that every cal lab provides is too course.
>  
> It hides (skips over) resonances in the probes.
>  
> Only a finer calibration step size will resolve this problem.
>  
> 
>  
>  
> 
>  
>  
> Here is my abbreviated story...
>  
>  
> 
>  
>  
> I started with data just like yours.
>  
> I had 6 probes: they were two model FP4000, and four of the HI6053.
>  
> 
>  
>  
> ...  amplifiers, chambers, height above table, orientation, etc>
>  
> 
>  
>  
> The root cause is the "normal" cal.
>  
> It uses a course step size in frequency.
>  
> When it is too course, it misses resonances in the probe.
>  
> Those resonances are significant, as much as +/- 20% in my equipment.
>  
> 
>  
>  
> To prove this, I sent a probe out for "enhanced" cal.
>  
> I requested both a "normal" cal and a higher resolution cal.
>  
> I asked for 5% steps below 1 GHz and 100 MHz steps above 1 GHz.
>  
> 
>  
>  
> When the data came back I plotted the cal factors on top of each other.
>  
> It was obvious.
>  
> The course cal points of a "normal" calibration will hide resonances that are
> +/- 20% deviations.
>  
>  
> (above sentence should be BOLD, UNDERLINE, asterisks)
>  
> 
>  
>  
> 
>  
>  
> My conclusion:  Any probe used for accredited test must have calibration data
> showing the resonances.
>  
> If it doesn't, then the lab is guaranteed to be over-testing and
> under-testing.
>  
> 
>  
>  
> DM me and I'll be glad to discuss.
>  
> 
>  
>  
> Patrick
>  
> 
>  
>  
> 
>  
>  
>  
> 
>  
> On Sun, Mar 4, 2018 at 8:33 PM, Schaefer, David <dschae...@tuvam.com> wrote:
>  
>> Ken,
>>  
>>  This data was not taken with 61000-4-3 primarily in mind. We do -4-3, but
>> also MIL, RTCA, and ISO testing. I should have had the probe at least 15 cm
>> for ISO or 30 cm for MIL like you said, but 10cm is how I took the data.
>>  
>>  Uniform field calibrations will be a concern eventually, but the variance is
>> my problem. This was not four probes set up on a bench next to each other.
>> This was data with one probe on the bench, centered in front of the antenna,
>> then removed and replaced as precisely as possible with the next probe.
>>  
>>  So if I do a single point cal for ISO 11452-2, one probe might tell me 100
>> V/m and another 140 V/m. I'll get questioned by customers if they fail one
>> day and pass another. This also runs into another issue - purchasing
>> amplifiers. If I 

Re: [PSES] Field probe calibration

[John Woodgate]

+/- 20% doesn't seem to be enough to explain the reported result. After 
all, assuming the +/- 20% is off the spectrum analyser, 1.2 is +1.6 dB 
and 0.8 is -1.9 dB. These are small, but not negligible. If the +/-20% 
relates to power, they are even smaller in dB, of course.


John Woodgate OOO-Own Opinions Only
J M Woodgate and Associates www.woodjohn.uk
Rayleigh, Essex UK

On 2018-03-05 15:57, Patrick wrote:

Hi David -

I had this same problem.
I'm actually glad to see another engineer looking into this!
The answer is not test setup,
    not ground plane,
    not distance to tabletop, etc.
Each of those can be significant, and should be controlled, but...


The problem you describe sounds exactly like one I had two years ago.
If it is the same problem, the root cause is the *probe calibration*.
The "normal" calibration data that every cal lab provides is too course.
It hides (skips over) resonances in the probes.
Only a finer calibration step size will resolve this problem.


Here is my abbreviated story...

I started with data just like yours.
I had 6 probes: they were two model FP4000, and four of the HI6053.

... antennas, amplifiers, chambers, height above table, orientation, etc>


The root cause is the "normal" cal.
It uses a course step size in frequency.
When it is too course, it misses resonances in the probe.
Those resonances are significant, as much as +/- 20% in my equipment.

To prove this, I sent a probe out for "enhanced" cal.
I requested both a "normal" cal and a higher resolution cal.
I asked for 5% steps below 1 GHz and 100 MHz steps above 1 GHz.

When the data came back I plotted the cal factors on top of each other.
It was obvious.
The course cal points of a "normal" calibration will hide resonances 
that are +/- 20% deviations.

(above sentence should be BOLD, UNDERLINE, asterisks)


My conclusion:  Any probe used for accredited test must have 
calibration data showing the resonances.
If it doesn't, then the lab is guaranteed to be over-testing and 
under-testing.


DM me and I'll be glad to discuss.

Patrick



On Sun, Mar 4, 2018 at 8:33 PM, Schaefer, David <dschae...@tuvam.com 
<mailto:dschae...@tuvam.com>> wrote:


Ken,

This data was not taken with 61000-4-3 primarily in mind. We do
-4-3, but also MIL, RTCA, and ISO testing. I should have had the
probe at least 15 cm for ISO or 30 cm for MIL like you said, but
10cm is how I took the data.

Uniform field calibrations will be a concern eventually, but the
variance is my problem. This was not four probes set up on a bench
next to each other. This was data with one probe on the bench,
centered in front of the antenna, then removed and replaced as
precisely as possible with the next probe.

So if I do a single point cal for ISO 11452-2, one probe might
tell me 100 V/m and another 140 V/m. I'll get questioned by
customers if they fail one day and pass another. This also runs
into another issue - purchasing amplifiers. If I specify an amp to
reach a desired field strength but when it shows up we can't hit
levels due to using a different field probe, there will be hell to
pay.

Standards are silent on probe orientation as well.  Do you
position the probe to maximize field strength? If I can get an
extra half a dB of power by having it an angle instead of straight
on, why not do that? I can save that amplifier cost - at least
until I get a new probe. The calibrations don't seem to mean that
much based on my data, so with a composite reading whichever probe
orientation gives me the highest field should be ok.

Also, any replies I make may be delayed. It seems like I usually
see a 4+ hour delay between when I email the listserve, and when
it is delivered.

Thanks,

David Schaefer


From: Ken Javor [mailto:ken.ja...@emccompliance.com
<mailto:ken.ja...@emccompliance.com>]
Sent: Sunday, March 04, 2018 12:17 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG <mailto:EMC-PSTC@LISTSERV.IEEE.ORG>
Subject: Re: [PSES] Field probe calibration

In turn:

It is not surprising at all that it takes less power to generate
the vertical field than the horizontal field. That's the effect of
the conducting ground plane. The OP doesn't say what spec they are
working to, but that is why MIL-STD-461 below 1 GHz has the probe
30 cm above the ground plane, to limit that effect.

Comments, such as Gert Gremmen's, that measurements in the
presence of a ground plane (or any conducting structure) are
useless, are themselves useless.  The comment reflects a
difference in standards of value.  If one is starving, food is the
most important priority. If one is asphyxiating, oxygen is the
primary need.  It is logically incorrect for two people suffering
these two conditions to point at each other and say the other one

Re: [PSES] Field probe calibration

[Patrick]

Hi David -

I had this same problem.
I'm actually glad to see another engineer looking into this!
The answer is not test setup,
not ground plane,
not distance to tabletop, etc.
Each of those can be significant, and should be controlled, but...


The problem you describe sounds exactly like one I had two years ago.
If it is the same problem, the root cause is the *probe calibration*.
The "normal" calibration data that every cal lab provides is too course.
It hides (skips over) resonances in the probes.
Only a finer calibration step size will resolve this problem.


Here is my abbreviated story...

I started with data just like yours.
I had 6 probes: they were two model FP4000, and four of the HI6053.

... 

The root cause is the "normal" cal.
It uses a course step size in frequency.
When it is too course, it misses resonances in the probe.
Those resonances are significant, as much as +/- 20% in my equipment.

To prove this, I sent a probe out for "enhanced" cal.
I requested both a "normal" cal and a higher resolution cal.
I asked for 5% steps below 1 GHz and 100 MHz steps above 1 GHz.

When the data came back I plotted the cal factors on top of each other.
It was obvious.
The course cal points of a "normal" calibration will hide resonances that
are +/- 20% deviations.
(above sentence should be BOLD, UNDERLINE, asterisks)


My conclusion:  Any probe used for accredited test must have calibration
data showing the resonances.
If it doesn't, then the lab is guaranteed to be over-testing and
under-testing.

DM me and I'll be glad to discuss.

Patrick



On Sun, Mar 4, 2018 at 8:33 PM, Schaefer, David <dschae...@tuvam.com> wrote:

> Ken,
>
> This data was not taken with 61000-4-3 primarily in mind. We do -4-3, but
> also MIL, RTCA, and ISO testing. I should have had the probe at least 15 cm
> for ISO or 30 cm for MIL like you said, but 10cm is how I took the data.
>
> Uniform field calibrations will be a concern eventually, but the variance
> is my problem. This was not four probes set up on a bench next to each
> other. This was data with one probe on the bench, centered in front of the
> antenna, then removed and replaced as precisely as possible with the next
> probe.
>
> So if I do a single point cal for ISO 11452-2, one probe might tell me 100
> V/m and another 140 V/m. I'll get questioned by customers if they fail one
> day and pass another. This also runs into another issue - purchasing
> amplifiers. If I specify an amp to reach a desired field strength but when
> it shows up we can't hit levels due to using a different field probe, there
> will be hell to pay.
>
> Standards are silent on probe orientation as well.  Do you position the
> probe to maximize field strength? If I can get an extra half a dB of power
> by having it an angle instead of straight on, why not do that? I can save
> that amplifier cost - at least until I get a new probe. The calibrations
> don't seem to mean that much based on my data, so with a composite reading
> whichever probe orientation gives me the highest field should be ok.
>
> Also, any replies I make may be delayed. It seems like I usually see a 4+
> hour delay between when I email the listserve, and when it is delivered.
>
> Thanks,
>
> David Schaefer
>
>
> From: Ken Javor [mailto:ken.ja...@emccompliance.com]
> Sent: Sunday, March 04, 2018 12:17 PM
> To: EMC-PSTC@LISTSERV.IEEE.ORG
> Subject: Re: [PSES] Field probe calibration
>
> In turn:
>
> It is not surprising at all that it takes less power to generate the
> vertical field than the horizontal field.  That's the effect of the
> conducting ground plane. The OP doesn't say what spec they are working to,
> but that is why MIL-STD-461 below 1 GHz has the probe 30 cm above the
> ground plane, to limit that effect.
>
> Comments, such as Gert Gremmen's, that measurements in the presence of a
> ground plane (or any conducting structure) are useless, are themselves
> useless.  The comment reflects a difference in standards of value.  If one
> is starving, food is the most important priority. If one is asphyxiating,
> oxygen is the primary need.  It is logically incorrect for two people
> suffering these two conditions to point at each other and say the other one
> is wrong about his priorities: they are both correct within the scope of
> their individual circumstances. The only logical observation that can be
> made is that oxygen needs to be supplied sooner than food, if the standard
> of value is immediate survival.
>
> In the world of goods slated for use in home, office and factory, the coin
> of the realm is accuracy and minimum uncertainty, so that qualifications
> everywhere result in a level economic playing field. Required field
> intensities (1/3/10 V/m) are ver

Re: [PSES] Field probe calibration

[Schaefer, David]

Ken,

This data was not taken with 61000-4-3 primarily in mind. We do -4-3, but also 
MIL, RTCA, and ISO testing. I should have had the probe at least 15 cm for ISO 
or 30 cm for MIL like you said, but 10cm is how I took the data.

Uniform field calibrations will be a concern eventually, but the variance is my 
problem. This was not four probes set up on a bench next to each other. This 
was data with one probe on the bench, centered in front of the antenna, then 
removed and replaced as precisely as possible with the next probe.

So if I do a single point cal for ISO 11452-2, one probe might tell me 100 V/m 
and another 140 V/m. I'll get questioned by customers if they fail one day and 
pass another. This also runs into another issue - purchasing amplifiers. If I 
specify an amp to reach a desired field strength but when it shows up we can't 
hit levels due to using a different field probe, there will be hell to pay.

Standards are silent on probe orientation as well.  Do you position the probe 
to maximize field strength? If I can get an extra half a dB of power by having 
it an angle instead of straight on, why not do that? I can save that amplifier 
cost - at least until I get a new probe. The calibrations don't seem to mean 
that much based on my data, so with a composite reading whichever probe 
orientation gives me the highest field should be ok.

Also, any replies I make may be delayed. It seems like I usually see a 4+ hour 
delay between when I email the listserve, and when it is delivered.

Thanks,

David Schaefer


From: Ken Javor [mailto:ken.ja...@emccompliance.com]
Sent: Sunday, March 04, 2018 12:17 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Field probe calibration

In turn:

It is not surprising at all that it takes less power to generate the vertical 
field than the horizontal field.  That's the effect of the conducting ground 
plane. The OP doesn't say what spec they are working to, but that is why 
MIL-STD-461 below 1 GHz has the probe 30 cm above the ground plane, to limit 
that effect.

Comments, such as Gert Gremmen's, that measurements in the presence of a ground 
plane (or any conducting structure) are useless, are themselves useless.  The 
comment reflects a difference in standards of value.  If one is starving, food 
is the most important priority. If one is asphyxiating, oxygen is the primary 
need.  It is logically incorrect for two people suffering these two conditions 
to point at each other and say the other one is wrong about his priorities: 
they are both correct within the scope of their individual circumstances. The 
only logical observation that can be made is that oxygen needs to be supplied 
sooner than food, if the standard of value is immediate survival.

In the world of goods slated for use in home, office and factory, the coin of 
the realm is accuracy and minimum uncertainty, so that qualifications 
everywhere result in a level economic playing field. Required field intensities 
(1/3/10 V/m) are very low compared to the world of vehicle EMI testing (as high 
as 200 V/m, sometimes beyond), so that (again relative) low power amplifiers 
may be used with antennas separated from the test area by three meters instead 
of one, facilitating the calibration of a quiet zone in the complete and utter 
absence of any conducting surfaces, because the end-item use does not include 
installation on or near a conducting ground plane.

This is all in sharp contrast to the qualification of equipment slated for use 
on a metal or partially metallic vehicle.  The ground plane is of material use 
in reducing the intensity of the horizontal field near it, as noted in the OP 
and taken advantage of by the very standards that deal with such 
qualifications: the ground plane is our friend. Let us count the ways:

As mentioned above, the ground plane reduces the intensity of a horizontally 
polarized field in its immediate vicinity.

The presence of a ground plane causes cables in its vicinity to react to fields 
not as an antenna as in the 61000-4-3 and 61000-4-6 paradigm, but as a 
transmission line.  Transmission lines radiate less per unit of current they 
carry, and couple less power from an incident field, than do antennas. Given 
the very stringent RE and RS requirements in vehicle standards, we need all the 
help we can get.

And finally, metallic equipment enclosures bonded to a ground plane allows 
filters to efficiently shunt incoming noise to the ground plane and away from 
internal circuitry, and perform that same function for noise currents coupled 
to shields that terminate in a low impedance manner to the exterior of such 
metallic equipment enclosures.

Now having dealt with Gert - his recurring comment about the futility of 
vehicle EMI testing re ground planes consistently eliciting the above response 
from me, ad infinitum and ad nauseum, lets look at the OP provided test data, 
especially in light of the 61000-4-3 required UFA (uniform field area

Re: [PSES] Field probe calibration

[Ken Javor]

Where below I said the measurements were within 6 dB of each other, I should
have said 3 dB. I got confused and was thinking of the values as field
intensities, not the power required to achieve a given field intensity.

Ken Javor
Phone: (256) 650-5261



From: Ken Javor <ken.ja...@emccompliance.com>
Reply-To: Ken Javor <ken.ja...@emccompliance.com>
Date: Sun, 4 Mar 2018 12:16:41 -0600
To: <EMC-PSTC@LISTSERV.IEEE.ORG>
Conversation: [PSES] Field probe calibration
Subject: Re: [PSES] Field probe calibration

In turn:

It is not surprising at all that it takes less power to generate the
vertical field than the horizontal field.  That¹s the effect of the
conducting ground plane. The OP doesn¹t say what spec they are working to,
but that is why MIL-STD-461 below 1 GHz has the probe 30 cm above the ground
plane, to limit that effect.

Comments, such as Gert Gremmen¹s, that measurements in the presence of a
ground plane (or any conducting structure) are useless, are themselves
useless.  The comment reflects a difference in standards of value.  If one
is starving, food is the most important priority. If one is asphyxiating,
oxygen is the primary need.  It is logically incorrect for two people
suffering these two conditions to point at each other and say the other one
is wrong about his priorities: they are both correct within the scope of
their individual circumstances. The only logical observation that can be
made is that oxygen needs to be supplied sooner than food, if the standard
of value is immediate survival.

In the world of goods slated for use in home, office and factory, the coin
of the realm is accuracy and minimum uncertainty, so that qualifications
everywhere result in a level economic playing field. Required field
intensities (1/3/10 V/m) are very low compared to the world of vehicle EMI
testing (as high as 200 V/m, sometimes beyond), so that (again relative) low
power amplifiers may be used with antennas separated from the test area by
three meters instead of one, facilitating the calibration of a quiet zone in
the complete and utter absence of any conducting surfaces, because the
end-item use does not include installation on or near a conducting ground
plane.

This is all in sharp contrast to the qualification of equipment slated for
use on a metal or partially metallic vehicle.  The ground plane is of
material use in reducing the intensity of the horizontal field near it, as
noted in the OP and taken advantage of by the very standards that deal with
such qualifications: the ground plane is our friend. Let us count the ways:

As mentioned above, the ground plane reduces the intensity of a horizontally
polarized field in its immediate vicinity.

The presence of a ground plane causes cables in its vicinity to react to
fields not as an antenna as in the 61000-4-3 and 61000-4-6 paradigm, but as
a transmission line.  Transmission lines radiate less per unit of current
they carry, and couple less power from an incident field, than do antennas.
Given the very stringent RE and RS requirements in vehicle standards, we
need all the help we can get.

And finally, metallic equipment enclosures bonded to a ground plane allows
filters to efficiently shunt incoming noise to the ground plane and away
from internal circuitry, and perform that same function for noise currents
coupled to shields that terminate in a low impedance manner to the exterior
of such metallic equipment enclosures.

Now having dealt with Gert ­ his recurring comment about the futility of
vehicle EMI testing re ground planes consistently eliciting the above
response from me, ad infinitum and ad nauseum, lets look at the OP provided
test data, especially in light of the 61000-4-3 required UFA (uniform field
area) uniformity requirement of +6 dB, -0 dB for 75% of the required sixteen
measurement points.

What I see is that for a given polarization and frequency every single
position measured is within 6 dB of the others.  In the immediate presence
of a ground plane, no less!  The cup is not half full ­ the cornucopia is
overflowing.  This performance greatly exceeds the MIL-STD-461 requirement:
there is no requirement for multiple measurement points, and if such are
used, the only requirement is to use the average of the measured points as
the leveling field intensity. In other such standards, such as RTCA/DO-160,
there is a requirement to precalibrate the field in the absence of the test
sample; I would say that the OP test data is evidence of an excellent
chamber.

If I wanted minimal variation between various positions down the length of a
ground plane, I would not use an aperture antenna such as a DRG horn, but
rather one with constant beamwidth vs. frequency, such as a log periodic.
Assuming I could get the required field intensity with the amplifiers at
hand.

Finally, while all the standards of which I am aware allow leveling on the
composite output of field probes looking in three orthogonal direction at
once, 

Re: [PSES] Field probe calibration

[Ken Javor]

Certainly below 1 GHz these probes are calibrated in a TEM cell with field
orientation parallel to the sensing element. Call it far field if you will,
but the point is that the sensing element is electrically short and drives a
high impedance capacitive load to get flat performance over the wide
frequency range.

Ken Javor
Phone: (256) 650-5261



From: "Schaefer, David" <dschae...@tuvam.com>
Reply-To: "Schaefer, David" <dschae...@tuvam.com>
Date: Sun, 4 Mar 2018 14:05:06 +
To: <EMC-PSTC@LISTSERV.IEEE.ORG>
Conversation: [PSES] Field probe calibration
Subject: Re: [PSES] Field probe calibration

All, 
 
Thanks for your all your input.
 
I don¹t think the listserve allows attachments, so I can¹t share setup
photos. The setup was like that used for RTCA, MIL STD, or automotive(ISO
11452-2). 90 cm high, appeox 3.5 meters long copper bench bonded to the
chamber wall. I have only done this limited range due to time constraints,
and the probes having a limited range of overlap. I did use the calibration
factors provided by the calibration lab or manufacturers. One concern is the
cal factors are widely different for the two probes of identical model, but
calibrated at two different places. One has a factor at 100 MHz of 0.44 dB,
the other 2.27 dB.
 
Should probes be calibrated in the far field? That might be difficult, as
one of these probes is rated for 10 kHz to 1 GHz; another for 10 MHz to 40
GHz. If they¹re used only in the near field, a near field calibration makes
sense.  I suppose the same could be said for antennas ­ we get 1, 3, or 10
meter factors from a calibration, but I think all probes are calibrated at
the same distance. I recall a cal house telling me once that all the probes
they do are calibrated at 30 cm.
 
Probe construction is different, and might have a major impact. That ties
back in to my original concern ­ isn¹t the calibration supposed to ensure
that each probe will return identical results in the presence of an
identical field? 
 
I will plan to take measurements on a 90 cm non-conductive bench, and
farther from the chamber walls. I¹d like to see that data as well. Perhaps
uniform field calibrations to IEC 61000-4-3 would be more consistent.
 
Frankly, these results concern me. Do you tell Ford, Boeing, or the DOD that
you don¹t really know what your field strength is? Yes, it¹s all calibrated
equipment, but your actual field could be +/- 3dB due to just probe error.
 
Thanks,
 
David Schaefer
 
 

From: Cortland Richmond [mailto:k...@earthlink.net]
Sent: Sunday, March 04, 2018 7:02 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Field probe calibration
 
I'm with Gert.


Anything "antennas" is  checked  in the far-field -- especially if testing
for accuracy. 

I'm a BIG fan of near-field probing for relative measurements and localizing
emissions, but we use probes appropriate to what we are looking for; if I
wanted to "calibrate" one there, I'd use a known current on a wire/trace  or
a known voltage on a small plate -- and not trust *that* much.

 

Cortland Richmond



On 3/4/18 5:35 AM, Gert Gremmen; ce-test wrote:
> 
> IMHO all probes are calibrated under far field conditions.
> 
> In general: Using probes in the proximity (< lambda) of anything conductive
> (including ground planes at 10 cm and including EUT) makes the measurement
> data useless. 
> 
> As James correctly states, the construction of the probe makes this effect
> different per type of probe, be it the construction, the size of battery or
> electronics on board or the lead (fiber or copper) , as long a other
> conductors are in proximity the read out has no relation to calibration data
> anymore.
> 
> Using a probe near a ground plane, such as usual in automotive test set ups,
> indeed says not much about the test level of the EUT.
> 
>  
> 
> Repeating this test under far field conditions, preferable on an antenna
> calibration facility, might give you much better results. (not that you are
> allowed to generate this much of power on air ;<)
> 
> Gert Gremmen
> 
>  
> 
> On 4-3-2018 11:06, James Pawson (U3C) wrote:
>> Hi David,
>>  
>> An interesting set of results! I¹m going to ask some questions that I¹m sure
>> you¹ve already considered so please bear with me being Captain B. Obvious.
>>  
>> Do your field probes use frequency correction? I¹m not familiar with a wide
>> range of probes but my Narda PMM field probe has an internal calibration
>> table; you tell it what the field frequency you are applying is and it makes
>> the appropriate correction. However, looking at the typical correction data
>> from the manual (see PDF page 12 of this doc:
>> https://www.emctest.it/public/pages/strumentazione/elenco/Narda/EP%20600/Manu
>> ali/EP600-EP601EN-90302-2.02.pdf) it doesn¹t look like a large 

Re: [PSES] Field probe calibration

[Schaefer, David]

All,

Thanks for your all your input.

I don't think the listserve allows attachments, so I can't share setup photos. 
The setup was like that used for RTCA, MIL STD, or automotive(ISO 11452-2). 90 
cm high, appeox 3.5 meters long copper bench bonded to the chamber wall. I have 
only done this limited range due to time constraints, and the probes having a 
limited range of overlap. I did use the calibration factors provided by the 
calibration lab or manufacturers. One concern is the cal factors are widely 
different for the two probes of identical model, but calibrated at two 
different places. One has a factor at 100 MHz of 0.44 dB, the other 2.27 dB.

Should probes be calibrated in the far field? That might be difficult, as one 
of these probes is rated for 10 kHz to 1 GHz; another for 10 MHz to 40 GHz. If 
they're used only in the near field, a near field calibration makes sense.  I 
suppose the same could be said for antennas - we get 1, 3, or 10 meter factors 
from a calibration, but I think all probes are calibrated at the same distance. 
I recall a cal house telling me once that all the probes they do are calibrated 
at 30 cm.

Probe construction is different, and might have a major impact. That ties back 
in to my original concern - isn't the calibration supposed to ensure that each 
probe will return identical results in the presence of an identical field?

I will plan to take measurements on a 90 cm non-conductive bench, and farther 
from the chamber walls. I'd like to see that data as well. Perhaps uniform 
field calibrations to IEC 61000-4-3 would be more consistent.

Frankly, these results concern me. Do you tell Ford, Boeing, or the DOD that 
you don't really know what your field strength is? Yes, it's all calibrated 
equipment, but your actual field could be +/- 3dB due to just probe error.

Thanks,

David Schaefer


From: Cortland Richmond [mailto:k...@earthlink.net]
Sent: Sunday, March 04, 2018 7:02 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Field probe calibration


I'm with Gert.


Anything "antennas" is  checked  in the far-field -- especially if testing for 
accuracy.

I'm a BIG fan of near-field probing for relative measurements and localizing 
emissions, but we use probes appropriate to what we are looking for; if I 
wanted to "calibrate" one there, I'd use a known current on a wire/trace  or a 
known voltage on a small plate -- and not trust *that* much.



Cortland Richmond



On 3/4/18 5:35 AM, Gert Gremmen; ce-test wrote:

IMHO all probes are calibrated under far field conditions.

In general: Using probes in the proximity (< lambda) of anything conductive 
(including ground planes at 10 cm and including EUT) makes the measurement data 
useless.

As James correctly states, the construction of the probe makes this effect 
different per type of probe, be it the construction, the size of battery or 
electronics on board or the lead (fiber or copper) , as long a other conductors 
are in proximity the read out has no relation to calibration data anymore.

Using a probe near a ground plane, such as usual in automotive test set ups, 
indeed says not much about the test level of the EUT.



Repeating this test under far field conditions, preferable on an antenna 
calibration facility, might give you much better results. (not that you are 
allowed to generate this much of power on air ;<)

Gert Gremmen

On 4-3-2018 11:06, James Pawson (U3C) wrote:
Hi David,

An interesting set of results! I'm going to ask some questions that I'm sure 
you've already considered so please bear with me being Captain B. Obvious.

Do your field probes use frequency correction? I'm not familiar with a wide 
range of probes but my Narda PMM field probe has an internal calibration table; 
you tell it what the field frequency you are applying is and it makes the 
appropriate correction. However, looking at the typical correction data from 
the manual (see PDF page 12 of this doc: 
https://www.emctest.it/public/pages/strumentazione/elenco/Narda/EP%20600/Manuali/EP600-EP601EN-90302-2.02.pdf)
 it doesn't look like a large difference.

Is there a difference in the probe construction between the probes used? Some 
probes like the Narda one above have two antenna per axis whereas ones like 
this Amplifier Research probe - https://www.arworld.us/html/18200.asp?id=636 
only have one antenna per axis. Perhaps the proximity of copper plate makes a 
difference.

On the subject of copper plate, what are the differences without this present? 
What are the dimensions of it and are they significant at the frequencies 
selected?

Have you acquired just spot readings or a full frequency sweep? There may be 
some patterns in the frequency sweep data that give you more of a clue as to 
what's happening.

An interesting puzzle and I look forward to hearing about your results further!
All the best
James



From: Schaefer, David [mailto:dschae...@tuvam.com]
Sent: 04 March 2018 05:22
To: 

Re: [PSES] Field probe calibration

[Ken Javor]

EE.ORG>
Subject: Re: [PSES] Field probe calibration

   

I'm with Gert.
 
 
 Anything "antennas" is  checked  in the far-field -- especially if testing
for accuracy.  
 
 I'm a BIG fan of near-field probing for relative measurements and
localizing emissions, but we use probes appropriate to what we are looking
for; if I wanted to "calibrate" one there, I'd use a known current on a
wire/trace  or a known voltage on a small plate -- and not trust *that*
much. 
 
 


 
 

Cortland Richmond
 
 
 
 On 3/4/18 5:35 AM, Gert Gremmen; ce-test wrote:
 
 
>   
> 
> IMHO all probes are calibrated under far field conditions.
>  
> 
> In general: Using probes in the proximity (< lambda) of anything conductive
> (including ground planes at 10 cm and including EUT) makes the measurement
> data useless. 
>  
>  
> 
> As James correctly states, the construction of the probe makes this effect
> different per type of probe, be it the construction, the size of battery or
> electronics on board or the lead (fiber or copper) , as long a other
> conductors are in proximity the read out has no relation to calibration data
> anymore.
>  
> 
> Using a probe near a ground plane, such as usual in automotive test set ups,
> indeed says not much about the test level of the EUT.
>  
> 
> 
>  
>  
> 
> Repeating this test under far field conditions, preferable on an antenna
> calibration facility, might give you much better results. (not that you are
> allowed to generate this much of power on air ;<)
>  
>  
> 
> Gert Gremmen
>  
>  
>  
> On 4-3-2018 11:06, James Pawson (U3C) wrote:
>  
>  
>> 
>>  
>> 
>> Hi David,
>>  
>>  
>>  
>> An interesting set of results! I¹m going to ask some questions that I¹m sure
>> you¹ve already considered so please bear with me being Captain B. Obvious.
>>  
>>  
>>  
>> Do your field probes use frequency correction? I¹m not familiar with a wide
>> range of probes but my Narda PMM field probe has an internal calibration
>> table; you tell it what the field frequency you are applying is and it makes
>> the appropriate correction. However, looking at the typical correction data
>> from the manual (see PDF page 12 of this doc:
>> https://www.emctest.it/public/pages/strumentazione/elenco/Narda/EP%20600/Manu
>> ali/EP600-EP601EN-90302-2.02.pdf) it doesn¹t look like a large difference.
>>  
>>  
>>  
>> Is there a difference in the probe construction between the probes used? Some
>> probes like the Narda one above have two antenna per axis whereas ones like
>> this Amplifier Research probe - https://www.arworld.us/html/18200.asp?id=636
>> only have one antenna per axis. Perhaps the proximity of copper plate makes a
>> difference.
>>  
>>  
>>  
>> On the subject of copper plate, what are the differences without this
>> present? What are the dimensions of it and are they significant at the
>> frequencies selected?
>>  
>>  
>>  
>> Have you acquired just spot readings or a full frequency sweep? There may be
>> some patterns in the frequency sweep data that give you more of a clue as to
>> what¹s happening.
>>  
>>  
>>  
>> An interesting puzzle and I look forward to hearing about your results
>> further!
>>  
>> All the best
>>  
>> James
>>  
>>  
>>  
>>  
>>  
>>  
>>  
>>  
>>  
>> 
>> From: Schaefer, David [mailto:dschae...@tuvam.com]
>>  Sent: 04 March 2018 05:22
>>  To: EMC-PSTC@LISTSERV.IEEE.ORG
>>  Subject: [PSES] Field probe calibration
>>  
>>  
>>  
>>  
>>  
>> I took data with 4 field probes, 3 different models. All calibrated. Two
>> calibrations by the manufacturer, two by a reputable cal house.
>>  
>>  
>>  
>> 200-1000 MHz data, 10 MHz step size, 60 V/m level. I recorded the forward
>> power, and all equipment and software in the setup was the same, barring only
>> the measuring field probe and associated probe factors. Composite values
>> only. No 3-axis data as I don¹t have 3-axis calibration data for all probes.
>> Probes were 10 cm above a copper bench, DRG antenna 90 from the bench.
>>  
>>  
>>  
>> The results are not encouraging. The tables below show the results in watts
>> of forward power for select frequencies.
>>  
>>  
>>  
>> Antenna Horizontal ­ values in Watts
>>
>>       Probe 1   Probe 2   Probe 3   Probe 4   Max-Min(Watts)
>>   200 MHz   85.17   144.4   135.9   97.75   59.23
>>   220 MHz   9

Re: [PSES] Field probe calibration

[Cortland Richmond]

I'm with Gert.


Anything "antennas" is  checked  in the far-field -- especially if 
testing for accuracy.


I'm a BIG fan of near-field probing for relative measurements and 
localizing emissions, but we use probes appropriate to what we are 
looking for; if I wanted to "calibrate" one there, I'd use a known 
current on a wire/trace  or a known voltage on a small plate -- and not 
trust *that* much.



Cortland Richmond



On 3/4/18 5:35 AM, Gert Gremmen; ce-test wrote:


IMHO all probes are calibrated under far field conditions.

In general: Using probes in the proximity (< lambda) of anything 
conductive (including ground planes at 10 cm and including EUT) makes 
the measurement data useless.


As James correctly states, the construction of the probe makes this 
effect different per type of probe, be it the construction, the size 
of battery or electronics on board or the lead (fiber or copper) , as 
long a other conductors are in proximity the read out has no relation 
to calibration data anymore.


Using a probe near a ground plane, such as usual in automotive test 
set ups, indeed says not much about the test level of the EUT.



Repeating this test under far field conditions, preferable on an 
antenna calibration facility, might give you much better results. (not 
that you are allowed to generate this much of power on air ;<)


Gert Gremmen


On 4-3-2018 11:06, James Pawson (U3C) wrote:


Hi David,

An interesting set of results! I’m going to ask some questions that 
I’m sure you’ve already considered so please bear with me being 
Captain B. Obvious.


Do your field probes use frequency correction? I’m not familiar with 
a wide range of probes but my Narda PMM field probe has an internal 
calibration table; you tell it what the field frequency you are 
applying is and it makes the appropriate correction. However, looking 
at the typical correction data from the manual (see PDF page 12 of 
this doc: 
https://www.emctest.it/public/pages/strumentazione/elenco/Narda/EP%20600/Manuali/EP600-EP601EN-90302-2.02.pdf) 
it doesn’t look like a large difference.


Is there a difference in the probe construction between the probes 
used? Some probes like the Narda one above have two antenna per axis 
whereas ones like this Amplifier Research probe - 
https://www.arworld.us/html/18200.asp?id=636 only have one antenna 
per axis. Perhaps the proximity of copper plate makes a difference.


On the subject of copper plate, what are the differences without this 
present? What are the dimensions of it and are they significant at 
the frequencies selected?


Have you acquired just spot readings or a full frequency sweep? There 
may be some patterns in the frequency sweep data that give you more 
of a clue as to what’s happening.


An interesting puzzle and I look forward to hearing about your 
results further!


All the best

James

*From:*Schaefer, David [mailto:dschae...@tuvam.com]
*Sent:* 04 March 2018 05:22
*To:* EMC-PSTC@LISTSERV.IEEE.ORG
*Subject:* [PSES] Field probe calibration

I took data with 4 field probes, 3 different models. All calibrated. 
Two calibrations by the manufacturer, two by a reputable cal house.


200-1000 MHz data, 10 MHz step size, 60 V/m level. I recorded the 
forward power, and all equipment and software in the setup was the 
same, barring only the measuring field probe and associated probe 
factors. Composite values only. No 3-axis data as I don’t have 3-axis 
calibration data for all probes. Probes were 10 cm above a copper 
bench, DRG antenna 90 from the bench.


The results are not encouraging. The tables below show the results in 
watts of forward power for select frequencies.


Antenna Horizontal – values in Watts



Probe 1



Probe 2



Probe 3



Probe 4



Max-Min(Watts)

200 MHz



85.17



144.4



135.9



97.75



59.23

220 MHz



92.81



171.6



157.4



113.5



78.79

500 MHz



21.7



34.93



28.58



26.94



13.23

900 MHz



25.57



37.25



25.6



32.42



11.68

Antenna Vertical – values in Watts



Probe 1



Probe 2



Probe 3



Probe 4



Max-Min(Watts)

200 MHz



18.94



25.12



22.55



18.82



6.3

330 MHz



34.1



40.69



46.29



39.41



12.19

780 MHz



35.52



53.03



29.87



32.83



23.16

930 MHz



56.63



47.01



64.26



107.7



60.69

There are trends in the data. Probe 1 was usually the lowest. Probe 2 
was usually the highest, rarely the lowest.


If you want to talk field strength effects this will mean, depending 
on the probe, you could have an E-field 40% higher between two 
‘identical’ calibrations.  The large variance between 

Re: [PSES] Field probe calibration

[Gert Gremmen; ce-test]

IMHO all probes are calibrated under far field conditions.

In general: Using probes in the proximity (< lambda) of anything 
conductive (including ground planes at 10 cm and including EUT) makes 
the measurement data useless.


As James correctly states, the construction of the probe makes this 
effect different per type of probe, be it the construction, the size of 
battery or electronics on board or the lead (fiber or copper) , as long 
a other conductors are in proximity the read out has no relation to 
calibration data anymore.


Using a probe near a ground plane, such as usual in automotive test set 
ups, indeed says not much about the test level of the EUT.



Repeating this test under far field conditions, preferable on an antenna 
calibration facility, might give you much better results. (not that you 
are allowed to generate this much of power on air ;<)


Gert Gremmen


On 4-3-2018 11:06, James Pawson (U3C) wrote:


Hi David,

An interesting set of results! I’m going to ask some questions that 
I’m sure you’ve already considered so please bear with me being 
Captain B. Obvious.


Do your field probes use frequency correction? I’m not familiar with a 
wide range of probes but my Narda PMM field probe has an internal 
calibration table; you tell it what the field frequency you are 
applying is and it makes the appropriate correction. However, looking 
at the typical correction data from the manual (see PDF page 12 of 
this doc: 
https://www.emctest.it/public/pages/strumentazione/elenco/Narda/EP%20600/Manuali/EP600-EP601EN-90302-2.02.pdf) 
it doesn’t look like a large difference.


Is there a difference in the probe construction between the probes 
used? Some probes like the Narda one above have two antenna per axis 
whereas ones like this Amplifier Research probe - 
https://www.arworld.us/html/18200.asp?id=636 only have one antenna per 
axis. Perhaps the proximity of copper plate makes a difference.


On the subject of copper plate, what are the differences without this 
present? What are the dimensions of it and are they significant at the 
frequencies selected?


Have you acquired just spot readings or a full frequency sweep? There 
may be some patterns in the frequency sweep data that give you more of 
a clue as to what’s happening.


An interesting puzzle and I look forward to hearing about your results 
further!


All the best

James

*From:*Schaefer, David [mailto:dschae...@tuvam.com]
*Sent:* 04 March 2018 05:22
*To:* EMC-PSTC@LISTSERV.IEEE.ORG
*Subject:* [PSES] Field probe calibration

I took data with 4 field probes, 3 different models. All calibrated. 
Two calibrations by the manufacturer, two by a reputable cal house.


200-1000 MHz data, 10 MHz step size, 60 V/m level. I recorded the 
forward power, and all equipment and software in the setup was the 
same, barring only the measuring field probe and associated probe 
factors. Composite values only. No 3-axis data as I don’t have 3-axis 
calibration data for all probes. Probes were 10 cm above a copper 
bench, DRG antenna 90 from the bench.


The results are not encouraging. The tables below show the results in 
watts of forward power for select frequencies.


Antenna Horizontal – values in Watts



Probe 1



Probe 2



Probe 3



Probe 4



Max-Min(Watts)

200 MHz



85.17



144.4



135.9



97.75



59.23

220 MHz



92.81



171.6



157.4



113.5



78.79

500 MHz



21.7



34.93



28.58



26.94



13.23

900 MHz



25.57



37.25



25.6



32.42



11.68

Antenna Vertical – values in Watts



Probe 1



Probe 2



Probe 3



Probe 4



Max-Min(Watts)

200 MHz



18.94



25.12



22.55



18.82



6.3

330 MHz



34.1



40.69



46.29



39.41



12.19

780 MHz



35.52



53.03



29.87



32.83



23.16

930 MHz



56.63



47.01



64.26



107.7



60.69

There are trends in the data. Probe 1 was usually the lowest. Probe 2 
was usually the highest, rarely the lowest.


If you want to talk field strength effects this will mean, depending 
on the probe, you could have an E-field 40% higher between two 
‘identical’ calibrations.  The large variance between which probe was 
highest or lowest based on freq. is troubling, as is the clear 
difference between horizontal and vertical. I took additional data 
with two probes of the same model rotated around a center axis. I 
don’t have that all compiled, but just comparing one probe against 
itself, laying on the left, right, and bottom sides, results in up 20% 
difference in required power.


I have not read IEEE 519, but plan to soon. So my question to this 
group - do you think 

Re: [PSES] Field probe calibration

[James Pawson (U3C)]

Hi David,

 

An interesting set of results! I'm going to ask some questions that I'm sure
you've already considered so please bear with me being Captain B. Obvious.

 

Do your field probes use frequency correction? I'm not familiar with a wide
range of probes but my Narda PMM field probe has an internal calibration
table; you tell it what the field frequency you are applying is and it makes
the appropriate correction. However, looking at the typical correction data
from the manual (see PDF page 12 of this doc:
https://www.emctest.it/public/pages/strumentazione/elenco/Narda/EP%20600/Man
uali/EP600-EP601EN-90302-2.02.pdf) it doesn't look like a large difference.

 

Is there a difference in the probe construction between the probes used?
Some probes like the Narda one above have two antenna per axis whereas ones
like this Amplifier Research probe -
https://www.arworld.us/html/18200.asp?id=636 only have one antenna per axis.
Perhaps the proximity of copper plate makes a difference.

 

On the subject of copper plate, what are the differences without this
present? What are the dimensions of it and are they significant at the
frequencies selected?

 

Have you acquired just spot readings or a full frequency sweep? There may be
some patterns in the frequency sweep data that give you more of a clue as to
what's happening.

 

An interesting puzzle and I look forward to hearing about your results
further!

All the best

James

 

 

 

From: Schaefer, David [mailto:dschae...@tuvam.com] 
Sent: 04 March 2018 05:22
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: [PSES] Field probe calibration

 

I took data with 4 field probes, 3 different models. All calibrated. Two
calibrations by the manufacturer, two by a reputable cal house. 

 

200-1000 MHz data, 10 MHz step size, 60 V/m level. I recorded the forward
power, and all equipment and software in the setup was the same, barring
only the measuring field probe and associated probe factors. Composite
values only. No 3-axis data as I don't have 3-axis calibration data for all
probes. Probes were 10 cm above a copper bench, DRG antenna 90 from the
bench. 

 

The results are not encouraging. The tables below show the results in watts
of forward power for select frequencies. 

 

Antenna Horizontal - values in Watts


 

Probe 1

Probe 2

Probe 3

Probe 4

Max-Min(Watts)


200 MHz

85.17

144.4

135.9

97.75

59.23


220 MHz

92.81

171.6

157.4

113.5

78.79


500 MHz

21.7

34.93

28.58

26.94

13.23


900 MHz

25.57

37.25

25.6

32.42

11.68

 

Antenna Vertical - values in Watts


 

Probe 1

Probe 2

Probe 3

Probe 4

Max-Min(Watts)


200 MHz

18.94

25.12

22.55

18.82

6.3


330 MHz

34.1

40.69

46.29

39.41

12.19


780 MHz

35.52

53.03

29.87

32.83

23.16


930 MHz

56.63

47.01

64.26

107.7

60.69

 

There are trends in the data. Probe 1 was usually the lowest. Probe 2 was
usually the highest, rarely the lowest. 

 

If you want to talk field strength effects this will mean, depending on the
probe, you could have an E-field 40% higher between two 'identical'
calibrations.  The large variance between which probe was highest or lowest
based on freq. is troubling, as is the clear difference between horizontal
and vertical. I took additional data with two probes of the same model
rotated around a center axis. I don't have that all compiled, but just
comparing one probe against itself, laying on the left, right, and bottom
sides, results in up 20% difference in required power.  

 

I have not read IEEE 519, but plan to soon. So my question to this group -
do you think field probe calibrations are accurate? How can we have
confidence in our results with such widely varying results? 

 

Thanks,

 

David Schaefer

 

 

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