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 
Reply-To: Ken Javor 
Date: Sun, 4 Mar 2018 12:16:41 -0600
To: 
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, it is unsurprising that 

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" 
Reply-To: "Schaefer, David" 
Date: Sun, 4 Mar 2018 14:05:06 +
To: 
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 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 - 

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]

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, it is unsurprising that this results in significant variations in
required power level.  Better testing results when the test equipment allows
leveling on the polarization of interest. Although, as I said above, I
consider the cited test data below to be exemplary.

I would have been bragging to my colleagues, not complaining!

Ken Javor
Phone: (256) 650-5261



From: Cortland Richmond 
Reply-To: Cortland Richmond 
Date: Sun, 4 Mar 2018 08:01:31 -0500
To: 
Subject: 

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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