EMI Near Field Probing Basics

[metrologist]

This video caused me to buy a twelve dollar EMI probe set, so I felt you tea partiers needed to be infected too... 




And of course, accolades to our host...

[metrologist]

And if twelve buck is too steep for you...

[mawyatt]

Can one get a $12 Probe Set that produces reasonable/repeatable results?

Best,

[pdenisowski]

I actually just finished a video on near field probes - it should be uploaded to the Rohde & Schwarz Test and Measurement Fundamentals Playlist in a couple of weeks:

https://www.youtube.com/playlist?list=PLKxVoO5jUTlvsVtDcqrVn0ybqBVlLj2z8

(I'm told it will also be turned into a web page on the R&S website, but no URL yet)

I do have to say that I very much enjoyed Dave's videos on near field probes - really good stuff with a lot of solid practical advice.

Can one get a $12 Probe Set that produces reasonable/repeatable results?

I tried out a bunch of probes while doing "research" for my video.  The short answer, in my experience, is that there are differences in terms of things like sensitivity, frequency range, etc. between probe sets:  a spur you can clearly see with a probe from one set might not be visible using a similarly-sized probe from another set. 

I spent many years doing field interference hunting and joked that there were some emitters that you could find with just a wire coat hanger and an AM radio - you needed the "good" antenna for the medium-hard and hard ones.  The same thing applies to EMI debug - you can find the really egregious violations with more or less any probe, but the more difficult cases can often benefit from a better-quality probe.  YMMV

[metrologist]

I think they are like antennas. Maybe not so much the quality as other attributes of the design? I made a pretty good reflector bi-quad antenna as a feed for a 10-foot dish, out of basically coat hanger and fine chicken wire fence material. A little with a good VNA and voila! Who said 13 cm ATV could not go 25 miles los with a mere 50 mW? Maybe no one 

BTW, I may get access to a professional NF probe set and try a comparison - something like this...

https://www.testequipmentdepot.com/aaronia/accessories/probes/emc-near-field-probes-kit-pbs2-5-pa.htm

...but with a ball detector so I may roll my own of that style.

[pdenisowski]

BTW, I may get access to a professional NF probe set and try a comparison

That's pretty much what I did   One of the near field probe sets I used in my comparison was our (R&S) own HZ-15 set:

https://www.rohde-schwarz.com/us/products/test-and-measurement/oscilloscope-probes/emc-near-field-probes-for-oscilloscopes_63493-73798.html

There was a (third-party) review of them in EDN many years ago:

https://www.edn.com/review-rohde-schwarz-hz-15-near-field-probes/

From my own experiments, there absolutely is a difference in performance between "professional" and "hobbyist" probes.

If you do have a chance to do a comparison, you may want to consider preamplifier performance as well.  In my investigations, the performance of preamps intended for use with near field probes varies significantly, especially with regard to noise figure.

[metrologist]

I received my probes. Two of them did not detect any signal and perplex me. The SMA connector center pin is left floating. Is that proper? I don't see how they could work at all like this 



Let the  begin 

[metrologist]

Here is another picture. How could this possibly work? I bet they just forgot to lay out the center trace and just decided to sell them anyway. 

[Momchilo]

You can't remove the heat shrink tube. Now there is no longer a closed waveguide between the probe tip and the connector