EEVblog #1178 - Build a $10 DIY EMC Probe

[EEVblog]

How to make your own magnetic H-field EMC probe for $10 that performs identically to a $300 commercial probe!

[desertgreg]

Anyone have a link to the pre-amplifier or a similar one?

[glarsson]

Search for "rf amplifier module" or similar on eBay.

[Smokey]

I sorta feel bad for Tekbox.  There is a reason magicians don't talk about how the magic happens

[Fire Doger]

I sorta feel bad for Tekbox.  There is a reason magicians don't talk about how the magic happens

It's not something extremely secret, if you Google "H-field EMC probe" you can see the best practices for making one

I was also thinking of making a set of 4 or 2 on a 50x50  PCB with nice connectors and stuff, 10x PCBs cost like 15$ (from known company), you get x10 set of probes and they don't look like a sex toy

[Bud]

The coax in the video is semi- rigid one. Rigid coax has solid outer copper shield.

[artag]

I think the plastic coating is a method I was taught in high school (several years ago). That bubbly appearance where you stripped it away is fairly characteristic.

You have a drum with plastic particles in it, compressed air blown in to make it fluidised. Heat the object and stick it in the drum, the plastic particles melt onto the surface and  make a covering.

Usually done on steel - it holds the heat better and melts the particles for longer  - but pcb material might work with a few applications. Perhaps it's warmed up in an oven to smooth the outer surface.

Here's a company selling the outfit :

https://www.plasticcoatings.co.uk/plastic-coatings-processes/thermoplastic-dip-coating.php

[cowasaki]

I've seen these probes used for locating dead ICs etc as well.  Is it possible to get any kind of useful reading with a scope?  Not everyone has a spectrum analyser on their bench :-)

[wilfred]

Anyone have a link to the pre-amplifier or a similar one?

I think this one is similar


https://www.ebay.com.au/itm/292353124631

[richnormand]

Nice video Dave.

Could you have used an isolated coax instead of bare metal, a tab of RTV silicone at the connection and done away with the plastic coating?
I relate to the shorting out the circuit you are testing but at the other end would it might be a good idea use a DC blocking connector to you spectrum analyser, just in case the probe touches something even though you are protected by the outer shield? I know my HP8561E  has a 0 DC MAX warning at the input connector or can you trust the coupling cap in the amp for that?

I found the technique most useful to find a dead coupling capacitor to an MMC before.
It was fairly high frequency but my homemade probe to the SA worked great

See post # 5 and 7:
https://www.eevblog.com/forum/repair/rohde-and-schwartz-cmu200-rxtx-module-issues/msg1030386/#msg1030386
The drop of signal was very noticeable and allowed me to zero-in on the trouble area, despite a lack of schematics.

Keep on the good work.

Cheers.

 

[EEVblog]

Anyone have a link to the pre-amplifier or a similar one?

Just search "Low noise amplifier"

[EEVblog]

Nice video Dave.
Could you have used an isolated coax instead of bare metal, a tab of RTV silicone at the connection and done away with the plastic coating?

Sure, but I didn't see those pre-terminated. I'm sure there are ones, so buy those if availabe.
I should have just slipped over some heatshink before soldering, but I had the can of stuff and thought that might be cool.

I relate to the shorting out the circuit you are testing but at the other end would it might be a good idea use a DC blocking connector to you spectrum analyser, just in case the probe touches something even though you are protected by the outer shield? I know my HP8561E  has a 0 DC MAX warning at the input connector or can you trust the coupling cap in the amp for that?

Sure you can trust the coupling cap in the amp, that's what it's for.

[EEVblog]

Anyone have a link to the pre-amplifier or a similar one?

I think this one is similar
https://www.ebay.com.au/itm/292353124631

Yep, that's identical.
I'm sure any of them would work though.

[EEVblog]

The coax in the video is semi- rigid one. Rigid coax has solid outer copper shield.

Yes, I know. My Australian brain just shortens stuff.

[johnlsenchak]

Very interesting   video  !

[Bud]

There is liquid plasti-dip, you just dip the thing in it and it makes nice even coating.

[EEVblog]

There is liquid plasti-dip, you just dip the thing in it and it makes nice even coating.

Sounds better, the spray was pretty crap.

[drussell]

There is liquid plasti-dip, you just dip the thing in it and it makes nice even coating.

Sounds better, the spray was pretty crap.

I've only ever seen the "dip" version, I didn't even know they made a spray version of Plasti-dip until this video.

[EEVblog]

There is liquid plasti-dip, you just dip the thing in it and it makes nice even coating.

Sounds better, the spray was pretty crap.

I've only ever seen the "dip" version, I didn't even know they made a spray version of Plasti-dip until this video.

Search ebay for plasti-dip and you can't find anything but the spray

[drussell]

There is liquid plasti-dip, you just dip the thing in it and it makes nice even coating.

Sounds better, the spray was pretty crap.

I've only ever seen the "dip" version, I didn't even know they made a spray version of Plasti-dip until this video.

Search ebay for plasti-dip and you can't find anything but the spray

Really?

https://www.ebay.ca/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=plasti-dip+14.5+oz



Edit:  This kit looks interesting:

https://www.ebay.ca/itm/22-oz-PLASTI-DIP-Create-Your-Color-KIT-Tint-Plastic-Dip-Tintable-Plasti-Dip-NEW/331502778292

They've apparently come a long way since I first saw it in the old screw-top metal cans many years ago at my local electronics store.

[floobydust]

At work we bought the Rohde & Schwarz HZ-15 EMI probe set. Very nice and almost a $1,000 per probe around $5K for the set, guaranteed flat response.
Of course idiot engineer broke one  I took it apart to fix it and the wand is a pen! For $1,000 I thought custom molded etc, no it's a ball point pen body...

beehive Electronics is a low cost source, I think the main body is a PCB inside the dip. Bigger and not as elegant as the R&S.

[johnmx]

An old thread regarding this matter:
https://www.eevblog.com/forum/projects/diy-magentic-field-probes/

[rlagore]

Thanks for the video Dave! For my first contribution to the forums, attached is a photo of the H-field probes we have in our lab. They vary widely in build quality and performance. You'll notice that we shield the notch in our probes with some copper tape over electrical or Kapton tape. Apparently this helps shield against E-fields. In our lab we build RF resonators and antennas (or "coils") for high field MRI research applications. The decoupled double probes on the left are for sniffing the resonant frequency of various structures.

[Gary350z]

Dave,
Nice video, but please explain how this probe picks up the magnetic field.

[drussell]

Dave,
Nice video, but please explain how this probe picks up the magnetic field.

Basic electromagnetic field theory.    https://en.wikipedia.org/wiki/Electromagnetic_radiation



An alternating magnetic field sets up an electric field (or vice versa) propagating outwards at a 90 degree angle to each other, somewhat like a chain, (except that the maxima of each occurs in phase, rather than interleaved like it would be if it were a chain.)  This is the basic fundamental principle underlying everything from radio waves to magnetic transformers, motors, etc.



The fundamentally linked nature of these fields is one of the absolute foundations of pretty much everything electronic that has come since the initial discovery nearly two centuries ago. 

[casinada]

This place sells some RF stuff but they don't show any specs   
http://store.newae.com/rf/

[bugli]

How it compares to an oscilloscope probe with its ground clip connected to the tip, forming a loop?

[desertgreg]

Thanks!  I found a few after searching for 'amplifier' rather than 'preamplifier'.  Is there a difference?  (sorry for my ignorance!)

[Yansi]

This place sells some RF stuff but they don't show any specs   
http://store.newae.com/rf/

Rofl! What a store! Reselling aliexpress at 20x the price.

Wow. Look at this!  Woudln't you want one for just $55? 
http://store.newae.com/h-field-probe-old-version/

[kahuna0k]

What about higher frequencies? And what about the smaller H-probes? I suppose the one Dave did is the easiest, but making a nice circle at the size of the most precise one doesn't seem as easy.

Also, could we use the TG to characterize their response and get some idea of how they behave if we don't have the real probes to validate that they are good?

[taydin]

Here is a hypothetical question guys: Let's say that Shariar (TheSignalPath guy) built an active probe that works up to 13 GHz and started selling it for $100. He has the knowledge AND the gear to do it. The going rate for keysight is $1K per GHz, so this would be about $13K. What would happen? My guess is that Keysight would contact him and offer him a very generous amount of money to make him stop selling it What is your guess?

[tautech]

An old thread regarding this matter:
https://www.eevblog.com/forum/projects/diy-magentic-field-probes/

Another:
https://www.eevblog.com/forum/testgear/new-affordable-emc-probe-set-at-a-bargain-price-from-ariel-rocholl_s-lab/

His shop indicates out of stock for the full set:
https://www.seeedstudio.com/RF-Explorer-Near-Field-Antenna-Kit-p-2784.html

However this one is still available:
https://www.seeedstudio.com/RF-Explorer-H-Loop-Near-Field-Antenna-RFEAN2-p-2720.html
And for a properly characterized probe and with a datasheet for $ 27.50 it's so cheap you wouldn't even consider trying to make one.

[Yansi]

My guess is that Shahriar would not do that, as that is too much trouble for little income. So he would likely price it appropriately, if he would ever thought about doing so.

[santiall]

I got myself a set of Rigol NFP-3 for about 200USD but there are some really cheap ones in taobao (no affiliation with the seller):
https://item.taobao.com/item.htm?spm=a1z0d.6639537.1997196601.4.310f58868hvelq&id=552095130623

[Smokey]

Here is a hypothetical question guys: Let's say that Shariar (TheSignalPath guy) built an active probe that works up to 13 GHz and started selling it for $100. He has the knowledge AND the gear to do it. The going rate for keysight is $1K per GHz, so this would be about $13K. What would happen? My guess is that Keysight would contact him and offer him a very generous amount of money to make him stop selling it What is your guess?

This is actually an easy one. 
Companies pay for the brand name stuff from a few reasons
1). Support.  If it breaks, you get it fixed or replaced fast.  Down time in a lab costs money.  Lots of it.
2) consistency.  If you buy 5 of something from a big name, they will all work the same.  They will also work the same as the one in the lab across the county. 
3). Reliability.  If you can't trust your measurements you are wasting your time.  That includes having reliability over the life of the product, which is typically a long time for big name stuff
4). Lower risk.  You have a much lower chance of having to justify purchasing big name brand equipment than "some dude on the internet".   It's an easier business decision considering there are budgets for this stuff.

Of course there are exceptions and examples of big name stuff violating all that stuff.  But it's generally the way it is. 
Big name companies don't feel and pain for small shops and hobbiest buying alternatives.  They are after the big fish.

[Yansi]

Of course there are exceptions and examples of big name stuff violating all that stuff.  But it's generally the way it is. 
Big name companies don't feel and pain for small shops and hobbiest buying alternatives.  They are after the big fish.

Because they likely don't know better, or the think they know better.  Not really always

[nctnico]

I got myself a set of Rigol NFP-3 for about 200USD but there are some really cheap ones in taobao (no affiliation with the seller):
https://item.taobao.com/item.htm?spm=a1z0d.6639537.1997196601.4.310f58868hvelq&id=552095130623

The EMC probe kit from RF Explorer is even cheaper. So cheap that it is hardly worth your time building your own EMC probes I have some DIY probes but these tend to break very quickly and it isn't always obvious something is wrong with the RF probe.

[nctnico]

This is actually an easy one. 
Companies pay for the brand name stuff from a few reasons
1). Support.  If it breaks, you get it fixed or replaced fast.  Down time in a lab costs money.  Lots of it.
2) consistency.  If you buy 5 of something from a big name, they will all work the same.  They will also work the same as the one in the lab across the county. 
3). Reliability.  If you can't trust your measurements you are wasting your time.  That includes having reliability over the life of the product, which is typically a long time for big name stuff
4). Lower risk.  You have a much lower chance of having to justify purchasing big name brand equipment than "some dude on the internet".   It's an easier business decision considering there are budgets for this stuff.

Not quite true. Most of my current probes are bought by (big) companies. It is easier to get a signature for spending 200 euro then 4000 euro.

[tszaboo]

I got myself a set of Rigol NFP-3 for about 200USD but there are some really cheap ones in taobao (no affiliation with the seller):
https://item.taobao.com/item.htm?spm=a1z0d.6639537.1997196601.4.310f58868hvelq&id=552095130623

Here is a link for the laowei.

https://www.aliexpress.com/item/1PC-EMC-EMI-Near-Field-Probe-Conducted-Radiation-Correction-Simple-Magnetic-Field-Probe-9KHz-6GHz-Type/32966266773.html

And now, I shall convince myself that I dont need this.

[Deni]

Here is a nice article about the topic:

https://tel.archives-ouvertes.fr/tel-01757038/document

[Smokey]

This is actually an easy one. 
Companies pay for the brand name stuff from a few reasons
1). Support.  If it breaks, you get it fixed or replaced fast.  Down time in a lab costs money.  Lots of it.
2) consistency.  If you buy 5 of something from a big name, they will all work the same.  They will also work the same as the one in the lab across the county. 
3). Reliability.  If you can't trust your measurements you are wasting your time.  That includes having reliability over the life of the product, which is typically a long time for big name stuff
4). Lower risk.  You have a much lower chance of having to justify purchasing big name brand equipment than "some dude on the internet".   It's an easier business decision considering there are budgets for this stuff.

Not quite true. Most of my current probes are bought by (big) companies. It is easier to get a signature for spending 200 euro then 4000 euro.

Cool.  Link to your stuff?
I agree it's usually easier to get approval for a less expensive purchase, but when that 3800euro "savings" turns into tens of thousands of euros in damage control if something goes wrong then you have a much higher chance of someone getting thrown under the bus than if you just spent the 4000 upfront and the blame goes to big test equipment.

[floobydust]

For EMC you still need a multi $1,000's spectrum analyzer, so what is the point in using a $10 probe?  You buy the Lamborghini and put cheap tires on it.

You can do EMC on the cheap, but still have to apply some science.  How are these home-made probes tested?
I appreciated using probes that were actually tested and proven in their freq. response and didn't have many dB peaks and valleys, giving out false confidence.

[David Hess]

Jim Williams published the designs for a more specialized calibrated EMI sniffer probe and amplifier in Linear Technology application notes 70 and 118 intended for locating EMI sources very precisely.  I have often had satisfactory results by just shorting the ground lead to the tip of one of my x10 oscilloscope probes.

The same articles also discuss building a trigger probe and circuit to allow oscilloscope triggering without a galvanic connection which would introduce ground noise.

[nctnico]

For EMC you still need a multi $1,000's spectrum analyzer, so what is the point in using a $10 probe?  You buy the Lamborghini and put cheap tires on it.

You can do EMC on the cheap, but still have to apply some science.  How are these home-made probes tested?
I appreciated using probes that were actually tested and proven in their freq. response and didn't have many dB peaks and valleys, giving out false confidence.

The thing is that you can't do accurate emissions testing outside a special (expensive) lab anyway. A simple spectrum analyser which goes to 1.5GHz will do 99% of the emissions testing in your own lab. The usual way of doing things is to go for pre-compliance testing, figure out at which frequencies the limit is exceeded and by how much. Back in your own lab you can measure the frequencies to have a base line and test improvements from there. None of this requires calibrated equipment or probes.

[santiall]

The thing is that you can't do accurate emissions testing outside a special (expensive) lab anyway. A simple spectrum analyser which goes to 1.5GHz will do 99% of the emissions testing in your own lab. The usual way of doing things is to go for pre-compliance testing, figure out at which frequencies the limit is exceeded and by how much. Back in your own lab you can measure the frequencies to have a base line and test improvements from there. None of this requires calibrated equipment or probes.

I was writing exactly the same... You can pretty much debug EMC problems in the lab after a pre-scan without the need of calibrated equipment. You can even use the pre-scans to sort of calibrate the equipment or at least to know more or less where you are and do some correlations.

The main problem I see with DIY probes and the likes is that people around, either your superiors or customers, may think you are either a cheap-_rse, a mad scientist, etc. and question you, think you have no clue or the usual 'how can that be right with that yellow goo POS you bodged back in the shop'... On the other hand they also may think you are a genius and saved so much time and money to the company

[David Hess]

On the other hand they also may think you are a genius and saved so much time and money to the company.

If you are being paid to do this type of engineering, then building your own probes does not save time or money unless you need something which is not commercially available.  Unfortunately, many managers do not see it this way and will happily starve engineers of the resources needed to do their job effectively and then blame the engineer for low productively.

[santiall]

Definitely, it also depends on the size of the company and so on but we are on the same page here (been there, suffered that!)

[floobydust]

Jim Williams published the designs for a more specialized calibrated EMI sniffer probe and amplifier in Linear Technology application notes 70 and 118 intended for locating EMI sources very precisely...

I had zero fun winding that inductor, then trying to solder the ends  I think I gave up on it.
Probably could buy an SMT air-core inductor but still need to fit/connect it to the Faraday shield.
I found it difficult to make.

[ebclr]

Also in ebay but at a pricey tag

https://www.ebay.com/itm/9KHz-7GHz-EMC-EMI-near-field-simple-magnetic-field-probe-for-conducted-radiation/292912779768?_trkparms=aid%3D888007%26algo%3DDISC.MBE%26ao%3D1%26asc%3D55675%26meid%3De36e7f1daff941e58311d1702be71a10%26pid%3D100009%26rk%3D1%26rkt%3D1%26sd%3D292912598167%26itm%3D292912779768&_trksid=p2047675.c100009.m1982

[metrologist]

Jim Williams published the designs for a more specialized calibrated EMI sniffer probe and amplifier in Linear Technology application notes 70 and 118 intended for locating EMI sources very precisely...

I had zero fun winding that inductor, then trying to solder the ends  I think I gave up on it.
Probably could buy an SMT air-core inductor but still need to fit/connect it to the Faraday shield.
I found it difficult to make.

I want to give it a whirl, but I'm having a hard time visualizing how it's built.

[floobydust]

It's 10 turns of #34AWG wire (0.16mm dia.) on a 1.5mm form, like a toothpick.
The murderous part is soldering the coax on one end, and the brass Faraday shield on the other. It was too flimsy, even with lots of epoxy.

If I was to revisit this, I would just buy a 0603 chip air-core RF inductor and solder to it or make a slim pcb for the probe. I also was looking at adding a balun because the grounded (to spectrum analyzer) shield easily shorts to your PCB under test.
The R&S probe has an exposed, grounded bare metal tab which causes drama, sparks etc. for noobs.

A big area probe like OP, I do not find useful. Aside from finding an unshielded inductor or SMPS transformer gapped-core spewing flux, I'm usually looking at smaller things for EMC.

[joeqsmith]

Link to articles of the probes I handmade and use.   I use these without any sort of preamplifier.   They are good enough that I can normally isolate things to a single trace.   

https://www.eevblog.com/forum/rf-microwave/ferrite-bead-pcb-track-current-probe/msg1723385/#msg1723385

[wilfred]

I don't have a multi $1,000's spectrum analyser but I do have a Digilent Analog Discovery. Could you make meaningful measurements about a circuit with such limitations? Or with some other inexpensive device. One question I had was could you measure bypass effectiveness and therefore evaluate changes/improvements where needed? Even if only on a single or double layer board.

[Radiosonde]

These are mine...nice for rf development and comparing shielding.

Gesendet von meinem SM-J730F mit Tapatalk

[Mortymore]

I had an EMC DIY probe made a long time ago, out of RG58 cable and with a 50 resistor placed in the ring, if I recall correctly, from an Elektor magazine article. At the time I had some fun finding the horizontal sweep frequency of computer CRT monitors.

This weekend I built 2 EMC probes, Dave Jones inspired. Not yet terminated since I don't have liquid electrical tape, but they are partially insulated with heat shrink tube. The soldered joint is naturally still exposed.

Attached a photo showing the radiated signal from a 100 MHz crystal oscillator. The graph has a 100MHz CF and a 10MHz span.

EDIT: Attached the article "H-field sensor" from Elektor UK magazine December 1994. This probe is 50 terminated at the tip.

[bitwelder]

Hackaday post on a DIY EMC probe (https://hackaday.com/2019/04/24/a-diy-emc-probe-from-semi-rigid-coax-and-an-sdr/)
based on an article on rtl-sdr.com (https://www.rtl-sdr.com/creating-an-emc-probe-using-an-rtl-sdr-and-semi-rigid-coax/),
inspired by Dave's video

[jemangedeslolos]

Hello,

Nobody tried to design EMC probe directly on PCB ?
With the ridiculy low price we can have this day, it will be interesting

[EEVblog]

Nobody tried to design EMC probe directly on PCB ?
With the ridiculy low price we can have this day, it will be interesting

No point, you can buy a complete set for US$46
http://s.click.aliexpress.com/e/bMu5qeBI

[German_EE]

I'm OK with almost everything that is involved with building the Jim Williams probe including winding the coil. The only sticking point is the two slits in a very small tube, far too small to use a hacksaw. How do I carry out this step?

[G7PSK]

I have just made one of these using the rigid coax as Dave showed with a wide band RF amplifier. I tried it with a Nooelec nesdr smartee dongle have not found any near fields yet but it makes one heck of an antenna from comercial FM upwards have not had time yet to find it's upper limits.

[David Hess]

I'm OK with almost everything that is involved with building the Jim Williams probe including winding the coil. The only sticking point is the two slits in a very small tube, far too small to use a hacksaw. How do I carry out this step?

Hobby shops sell "razor" or "snap" saws (1) which use much thinner saw blades than hacksaws.  Thin slitting saws or abrasive disks on a rotary tool like a Dremel are another option but operation can be tricky unless the work piece and rotary tool can be anchored firmly.

(1) Search for "atlas snap saw".

[Gromitt]

I'm OK with almost everything that is involved with building the Jim Williams probe including winding the coil. The only sticking point is the two slits in a very small tube, far too small to use a hacksaw. How do I carry out this step?

Hobby shops sell "razor" or "snap" saws (1) which use much thinner saw blades than hacksaws.  Thin slitting saws or abrasive disks on a rotary tool like a Dremel are another option but operation can be tricky unless the work piece and rotary tool can be anchored firmly.

(1) Search for "atlas snap saw".

Or, as you are in Germany, search for 'Roco Bastelsäge' or 'Roco 10900' (They are the same thing, Roco makes them for Atlas)