EEVblog #1178 - Build a $10 DIY EMC Probe

[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.