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.