Bruce Carsten\'s \'EMI Sniffer Probe\'...

[server]

I\'ve many times made ad hoc sniffer coils for hunting out EMI &
found them invaluable. This more-refined implementation came
across my radar this morning, and seemed worthy of revisiting
for the group.

The EMI Sniffer Probe is a small pick-up coil for probing
high-frequency magnetic fields with an oscilloscope, featured
in Jim Williams\' classic AN118, Appendix E.

https://www.analog.com/media/en/technical-documentation/application-notes/AN118fb.pdf

The probe is a solenoid of 10 turns of #34 wire, 0.060\" diameter,
encased in a brass shielding tube that has been slit to avoid the
shorted turn. The coil is terminated into 50 ohms, and the whole
works are mounted to a BNC for the \'scope connection.

AN118 gives construction and use details vis a vis SMPS.

Insulated, this sort of thing would be handy for non-contact
tracing fast high-voltage currents.

I may build one into some semi-rigid coax, possibly with a ferrite
rod for tighter resolution.

Cheers,
James Arthur

 

[server]

On Sun, 16 Aug 2020 13:46:56 -0700 (PDT), dagmargoodboat@yahoo.com
wrote:

I\'ve many times made ad hoc sniffer coils for hunting out EMI &
found them invaluable. This more-refined implementation came
across my radar this morning, and seemed worthy of revisiting
for the group.

The EMI Sniffer Probe is a small pick-up coil for probing
high-frequency magnetic fields with an oscilloscope, featured
in Jim Williams\' classic AN118, Appendix E.

https://www.analog.com/media/en/technical-documentation/application-notes/AN118fb.pdf

The probe is a solenoid of 10 turns of #34 wire, 0.060\" diameter,
encased in a brass shielding tube that has been slit to avoid the
shorted turn. The coil is terminated into 50 ohms, and the whole
works are mounted to a BNC for the \'scope connection.

AN118 gives construction and use details vis a vis SMPS.

Insulated, this sort of thing would be handy for non-contact
tracing fast high-voltage currents.

I may build one into some semi-rigid coax, possibly with a ferrite
rod for tighter resolution.

Cheers,
James Arthur

If you\'re looking for EMI emitters, why shield the coil?

I sometimes hang a short piece of wire on the end of a coax, into a
spectrum analyzer. For mag fields, a cheap unshielded drum core
inductor works great.

Friday, trying to find my jitter problem, just waving a scope probe
around was all I needed. I have two dc/dc converters on my board, and
therorized that one or both were getting into my nearby timing ramps.
Parking the probe above each converter showed its switching frequency.

https://www.dropbox.com/s/g3ohf1538qth6wl/J270_E02.jpg?raw=1

Once I figured out the frequency of each converter, I varied the
trigger rate into the box. At some cardinal rates, I could see the
trigger rate heterodyning the jitter pattern. Neither dc/dc switch
rate corresponded. The thing that did correspond was the oscillation
frequency of an LDO.

Sometimes a good fet probe doesn\'t even need to touch a signal. Just
get close.

Electronics presents us with riddles to solve.




--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[server]

On Sunday, August 16, 2020 at 5:09:06 PM UTC-4, jla...@highlandsniptechnology.com wrote:

On Sun, 16 Aug 2020 13:46:56 -0700 (PDT), dagmargoodboat@yahoo.com
wrote:

I\'ve many times made ad hoc sniffer coils for hunting out EMI &
found them invaluable. This more-refined implementation came
across my radar this morning, and seemed worthy of revisiting
for the group.

The EMI Sniffer Probe is a small pick-up coil for probing
high-frequency magnetic fields with an oscilloscope, featured
in Jim Williams\' classic AN118, Appendix E.

https://www.analog.com/media/en/technical-documentation/application-notes/AN118fb.pdf

The probe is a solenoid of 10 turns of #34 wire, 0.060\" diameter,
encased in a brass shielding tube that has been slit to avoid the
shorted turn. The coil is terminated into 50 ohms, and the whole
works are mounted to a BNC for the \'scope connection.

AN118 gives construction and use details vis a vis SMPS.

Insulated, this sort of thing would be handy for non-contact
tracing fast high-voltage currents.

I may build one into some semi-rigid coax, possibly with a ferrite
rod for tighter resolution.

Cheers,
James Arthur

If you\'re looking for EMI emitters, why shield the coil?

To block the electrical field--you\'re hunting currents, not
capacitively-coupled voltages.

I sometimes hang a short piece of wire on the end of a coax, into a
spectrum analyzer. For mag fields, a cheap unshielded drum core
inductor works great.

Friday, trying to find my jitter problem, just waving a scope probe
around was all I needed. I have two dc/dc converters on my board, and
therorized that one or both were getting into my nearby timing ramps.
Parking the probe above each converter showed its switching frequency.

I do that too. Also, for mixed hash, trigger on the magic wand
probe, while viewing the hash on another channel. That freezes
the various hash components selectively, one-by-one.

https://www.dropbox.com/s/g3ohf1538qth6wl/J270_E02.jpg?raw=1

Once I figured out the frequency of each converter, I varied the
trigger rate into the box. At some cardinal rates, I could see the
trigger rate heterodyning the jitter pattern. Neither dc/dc switch
rate corresponded. The thing that did correspond was the oscillation
frequency of an LDO.

Sometimes a good fet probe doesn\'t even need to touch a signal. Just
get close.

Electronics presents us with riddles to solve.

Yep. I\'m intrigued with air-core power converters at the moment,
hence the appeal of B-field probes.

Cheers,
James

 

[Gerhard Hoffmann]

Am 16.08.20 um 23:25 schrieb dagmargoodboat@yahoo.com:

On Sunday, August 16, 2020 at 5:09:06 PM UTC-4, jla...@highlandsniptechnology.com wrote:

Sometimes a good fet probe doesn\'t even need to touch a signal. Just
get close.

Electronics presents us with riddles to solve.

Yep. I\'m intrigued with air-core power converters at the moment,
hence the appeal of B-field probes.

<
https://www.flickr.com/photos/137684711@N07/50234503206/in/dateposted-public/
>

This is my mag probe. At the end of the semi-rigid belongs a 0402
or 0603 pickup coil which is broken off.
The brass tube shields electrostatically. It has a slot at the tip.

The alu box has nothing to do with it, it\'s just that the stuff does
not roll away. It\'s for my new 12 GHz trigger prescaler in statu
nascendi for the sampling scope.


I don\'t remember where I got the idea from. Probably from EDN back in
time when men were men and EDN was a thumb thick bundle of interesting
things.

> Cheers,
Gerhard

 

[Lasse Langwadt Christensen]

https://youtu.be/2xy3Hm1_ZqI

 

[server]

On Sun, 16 Aug 2020 14:25:44 -0700 (PDT), dagmargoodboat@yahoo.com
wrote:

On Sunday, August 16, 2020 at 5:09:06 PM UTC-4, jla...@highlandsniptechnology.com wrote:
On Sun, 16 Aug 2020 13:46:56 -0700 (PDT), dagmargoodboat@yahoo.com
wrote:

I\'ve many times made ad hoc sniffer coils for hunting out EMI &
found them invaluable. This more-refined implementation came
across my radar this morning, and seemed worthy of revisiting
for the group.

The EMI Sniffer Probe is a small pick-up coil for probing
high-frequency magnetic fields with an oscilloscope, featured
in Jim Williams\' classic AN118, Appendix E.

https://www.analog.com/media/en/technical-documentation/application-notes/AN118fb.pdf

The probe is a solenoid of 10 turns of #34 wire, 0.060\" diameter,
encased in a brass shielding tube that has been slit to avoid the
shorted turn. The coil is terminated into 50 ohms, and the whole
works are mounted to a BNC for the \'scope connection.

AN118 gives construction and use details vis a vis SMPS.

Insulated, this sort of thing would be handy for non-contact
tracing fast high-voltage currents.

I may build one into some semi-rigid coax, possibly with a ferrite
rod for tighter resolution.

Cheers,
James Arthur

If you\'re looking for EMI emitters, why shield the coil?

To block the electrical field--you\'re hunting currents, not
capacitively-coupled voltages.

I sometimes hang a short piece of wire on the end of a coax, into a
spectrum analyzer. For mag fields, a cheap unshielded drum core
inductor works great.

Friday, trying to find my jitter problem, just waving a scope probe
around was all I needed. I have two dc/dc converters on my board, and
therorized that one or both were getting into my nearby timing ramps.
Parking the probe above each converter showed its switching frequency.

I do that too. Also, for mixed hash, trigger on the magic wand
probe, while viewing the hash on another channel. That freezes
the various hash components selectively, one-by-one.

https://www.dropbox.com/s/g3ohf1538qth6wl/J270_E02.jpg?raw=1

Once I figured out the frequency of each converter, I varied the
trigger rate into the box. At some cardinal rates, I could see the
trigger rate heterodyning the jitter pattern. Neither dc/dc switch
rate corresponded. The thing that did correspond was the oscillation
frequency of an LDO.

Sometimes a good fet probe doesn\'t even need to touch a signal. Just
get close.

Electronics presents us with riddles to solve.

Yep. I\'m intrigued with air-core power converters at the moment,
hence the appeal of B-field probes.

Fun. Maybe make a transformer from really thin kapton flex.

Cheers,
James

HP once sold a \"modulation domain analyzer.\" They had a cool 3d
diagram in an ad that showed a scope on one axis - voltage vs time -
and a spectrum analyzer on another axis - voltage vs frequency - and
proposed a new instrument on the 3rd axis that measured frequency vs
time, or maybe it was time vs time. They sold some but I don\'t think
it was popular.

I often see, say, time or period jitter and wonder what the source is.
If the time error vs time showed a 60 Hz component, I\'d know where to
look. Imagine a spectrum analysis of the discriminated time error. The
telecom people care about this.

A digital oscilloscope should be able to display time error vs time,
but I don\'t know of one that does.

I\'m seeing maybe 10 ps RMS jitter on my 25 ns range, just about an
inch from the two dc/dc converters. But that jitter includes my DDG
and my old Tek sampling scope, so it\'s actually less. One rough r.o.t.
is that a really good analog ramp has 1 part in 20,000 RMS jitter.

If I can commandeer some muscle, and clear off a square yard of bench
space, I\'ll drag up the monster LeCroy scope and get a better jitter
measurement.




--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[server]

On Sunday, August 16, 2020 at 6:12:51 PM UTC-4, Gerhard Hoffmann wrote:

Am 16.08.20 um 23:25 schrieb dagmargoodboat@yahoo.com:
On Sunday, August 16, 2020 at 5:09:06 PM UTC-4, jla...@highlandsniptechnology.com wrote:

Sometimes a good fet probe doesn\'t even need to touch a signal. Just
get close.

Electronics presents us with riddles to solve.

Yep. I\'m intrigued with air-core power converters at the moment,
hence the appeal of B-field probes.


https://www.flickr.com/photos/137684711@N07/50234503206/in/dateposted-public/


This is my mag probe. At the end of the semi-rigid belongs a 0402
or 0603 pickup coil which is broken off.
The brass tube shields electrostatically. It has a slot at the tip.

The alu box has nothing to do with it, it\'s just that the stuff does
not roll away. It\'s for my new 12 GHz trigger prescaler in statu
nascendi for the sampling scope.


I don\'t remember where I got the idea from. Probably from EDN back in
time when men were men and EDN was a thumb thick bundle of interesting
things.

Cheers,
Gerhard

Nice probe! I feel a bit silly I\'ve gone all this time without
making a nice one.

Since posting, I wound two coils, ten close-wound turns of #32
wire each. One was formed on a 0.058\" (1,5 mm) mandrel, the
other on a 0.082\" (2,1 mm) diameter mandrel.

They look very promising. I think they\'ll offer much better spacial
resolution than anything I\'ve done before, plus add useful
directivity.

A ferrite rod, if I can manage to machine one that small, could
improve the resolution and let me get the same signal from fewer
turns, raising the self-resonant frequency in the bargain.

Cheers,
James Arthur

 

[Klaus Kragelund]

On Monday, August 17, 2020 at 2:32:03 AM UTC+2, dagmarg...@yahoo.com wrote:

On Sunday, August 16, 2020 at 6:12:51 PM UTC-4, Gerhard Hoffmann wrote:
Am 16.08.20 um 23:25 schrieb dagmarg...@yahoo.com:
On Sunday, August 16, 2020 at 5:09:06 PM UTC-4, jla...@highlandsniptechnology.com wrote:

Sometimes a good fet probe doesn\'t even need to touch a signal. Just
get close.

Electronics presents us with riddles to solve.

Yep. I\'m intrigued with air-core power converters at the moment,
hence the appeal of B-field probes.


https://www.flickr.com/photos/137684711@N07/50234503206/in/dateposted-public/


This is my mag probe. At the end of the semi-rigid belongs a 0402
or 0603 pickup coil which is broken off.
The brass tube shields electrostatically. It has a slot at the tip.

The alu box has nothing to do with it, it\'s just that the stuff does
not roll away. It\'s for my new 12 GHz trigger prescaler in statu
nascendi for the sampling scope.


I don\'t remember where I got the idea from. Probably from EDN back in
time when men were men and EDN was a thumb thick bundle of interesting
things.

Cheers,
Gerhard
Nice probe! I feel a bit silly I\'ve gone all this time without
making a nice one.

Since posting, I wound two coils, ten close-wound turns of #32
wire each. One was formed on a 0.058\" (1,5 mm) mandrel, the
other on a 0.082\" (2,1 mm) diameter mandrel.

They look very promising. I think they\'ll offer much better spacial
resolution than anything I\'ve done before, plus add useful
directivity.

A ferrite rod, if I can manage to machine one that small, could
improve the resolution and let me get the same signal from fewer
turns, raising the self-resonant frequency in the bargain.

You can build it for 10 USD as shown on EEVblog

I just bought a 5 set version for 30 USD at Aliexpress, since I am lazy:

https://www.aliexpress.com/item/4000672321574.html

 

[server]

On Monday, August 17, 2020 at 3:23:51 AM UTC-4, Klaus Kragelund wrote:

On Monday, August 17, 2020 at 2:32:03 AM UTC+2, dagmarg...@yahoo.com wrote:
On Sunday, August 16, 2020 at 6:12:51 PM UTC-4, Gerhard Hoffmann wrote:
Am 16.08.20 um 23:25 schrieb dagmarg...@yahoo.com:
On Sunday, August 16, 2020 at 5:09:06 PM UTC-4, jla...@highlandsniptechnology.com wrote:

Sometimes a good fet probe doesn\'t even need to touch a signal. Just
get close.

Electronics presents us with riddles to solve.

Yep. I\'m intrigued with air-core power converters at the moment,
hence the appeal of B-field probes.


https://www.flickr.com/photos/137684711@N07/50234503206/in/dateposted-public/


This is my mag probe. At the end of the semi-rigid belongs a 0402
or 0603 pickup coil which is broken off.
The brass tube shields electrostatically. It has a slot at the tip.

The alu box has nothing to do with it, it\'s just that the stuff does
not roll away. It\'s for my new 12 GHz trigger prescaler in statu
nascendi for the sampling scope.


I don\'t remember where I got the idea from. Probably from EDN back in
time when men were men and EDN was a thumb thick bundle of interesting
things.

Cheers,
Gerhard
Nice probe! I feel a bit silly I\'ve gone all this time without
making a nice one.

Since posting, I wound two coils, ten close-wound turns of #32
wire each. One was formed on a 0.058\" (1,5 mm) mandrel, the
other on a 0.082\" (2,1 mm) diameter mandrel.

They look very promising. I think they\'ll offer much better spacial
resolution than anything I\'ve done before, plus add useful
directivity.

A ferrite rod, if I can manage to machine one that small, could
improve the resolution and let me get the same signal from fewer
turns, raising the self-resonant frequency in the bargain.


You can build it for 10 USD as shown on EEVblog

I just bought a 5 set version for 30 USD at Aliexpress, since I am lazy:

https://www.aliexpress.com/item/4000672321574.html

I can beat that--I was too lazy to order. I wound my coils on-the-spot
from buss wire for $0.00 previously, faster than you could click \"buy.\"

But my ad hoc coils never had anything close to the spacial-resolution
or directivity of Carsten\'s 10-turn x 1,5mm-diameter shielded coil.

I watched Lasse\'s EEVblog link, where Dave makes a single-turn
big-loop shielded pick up coil from semi-rigid coax, then goes
hunting for gross noise-making areas with a spectrum analyzer.

That\'s a fine \'finger-in-the-wind,\' but that\'s not Carsten\'s idea--
Carsten\'s pencil-lead-diameter \'microscope\' allows zooming in on
individual component leads and PCB traces, and qualitatively
non-contact probing the time-domain fields and currents.

(When I posted I was considering building a Carsten Sniffer from
semi-rigid coax, I meant \'locating the coil inside the coax shield,\'
not \'making coax-loops.\')
.-------.
.----| |
=+====================================| | |
| .------------. #######| | |
\'-|10-turn coil|---[50 ohms]---------| | BNC |
\'------------\' #######| | |
======================================| | |
\\ \'----| |
slit shield \'-------\'


And, Carsten\'s ten turns produce <calculates furiously> nearly
ten times the signal of a single turn, +20dB with no amplifier
needed.

Cheers,
James Arthur

 

[George Herold]

On Sunday, August 16, 2020 at 4:47:00 PM UTC-4, dagmarg...@yahoo.com wrote:

I\'ve many times made ad hoc sniffer coils for hunting out EMI &
found them invaluable. This more-refined implementation came
across my radar this morning, and seemed worthy of revisiting
for the group.

The EMI Sniffer Probe is a small pick-up coil for probing
high-frequency magnetic fields with an oscilloscope, featured
in Jim Williams\' classic AN118, Appendix E.

https://www.analog.com/media/en/technical-documentation/application-notes/AN118fb.pdf

The probe is a solenoid of 10 turns of #34 wire, 0.060\" diameter,
encased in a brass shielding tube that has been slit to avoid the
shorted turn. The coil is terminated into 50 ohms, and the whole
works are mounted to a BNC for the \'scope connection.

AN118 gives construction and use details vis a vis SMPS.

Insulated, this sort of thing would be handy for non-contact
tracing fast high-voltage currents.

I may build one into some semi-rigid coax, possibly with a ferrite
rod for tighter resolution.

Cheers,
James Arthur

Thanks James... I need to re-read the app note to get all the details.
I\'ve made much cruder things with a few turns of stiff magnet wire.
(say 20 AWG) and my x10 \'scope probe.

George H.

 

[server]

On Sunday, August 16, 2020 at 7:24:09 PM UTC-4, jla...@highlandsniptechnology.com wrote:

On Sun, 16 Aug 2020 14:25:44 -0700 (PDT), dagmargoodboat@yahoo.com
wrote:

On Sunday, August 16, 2020 at 5:09:06 PM UTC-4, jla...@highlandsniptechnology.com wrote:
On Sun, 16 Aug 2020 13:46:56 -0700 (PDT), dagmargoodboat@yahoo.com
wrote:

I\'ve many times made ad hoc sniffer coils for hunting out EMI &
found them invaluable. This more-refined implementation came
across my radar this morning, and seemed worthy of revisiting
for the group.

The EMI Sniffer Probe is a small pick-up coil for probing
high-frequency magnetic fields with an oscilloscope, featured
in Jim Williams\' classic AN118, Appendix E.

https://www.analog.com/media/en/technical-documentation/application-notes/AN118fb.pdf

The probe is a solenoid of 10 turns of #34 wire, 0.060\" diameter,
encased in a brass shielding tube that has been slit to avoid the
shorted turn. The coil is terminated into 50 ohms, and the whole
works are mounted to a BNC for the \'scope connection.

AN118 gives construction and use details vis a vis SMPS.

Insulated, this sort of thing would be handy for non-contact
tracing fast high-voltage currents.

I may build one into some semi-rigid coax, possibly with a ferrite
rod for tighter resolution.

Cheers,
James Arthur

If you\'re looking for EMI emitters, why shield the coil?

To block the electrical field--you\'re hunting currents, not
capacitively-coupled voltages.

I sometimes hang a short piece of wire on the end of a coax, into a
spectrum analyzer. For mag fields, a cheap unshielded drum core
inductor works great.

Friday, trying to find my jitter problem, just waving a scope probe
around was all I needed. I have two dc/dc converters on my board, and
therorized that one or both were getting into my nearby timing ramps.
Parking the probe above each converter showed its switching frequency.

I do that too. Also, for mixed hash, trigger on the magic wand
probe, while viewing the hash on another channel. That freezes
the various hash components selectively, one-by-one.

https://www.dropbox.com/s/g3ohf1538qth6wl/J270_E02.jpg?raw=1

Once I figured out the frequency of each converter, I varied the
trigger rate into the box. At some cardinal rates, I could see the
trigger rate heterodyning the jitter pattern. Neither dc/dc switch
rate corresponded. The thing that did correspond was the oscillation
frequency of an LDO.

Sometimes a good fet probe doesn\'t even need to touch a signal. Just
get close.

Electronics presents us with riddles to solve.

Yep. I\'m intrigued with air-core power converters at the moment,
hence the appeal of B-field probes.

Fun. Maybe make a transformer from really thin kapton flex.

These guys put 35W through a 10mm coreless PCB-printed transformer:
https://ieeexplore.ieee.org/document/6099785

That\'s cool.

Cheers,
James