EMC debugging - Near field Electric field probes 

Look for IMSAIGuy, he's pretty good at explaining things too.

Thanks so much!

Glad you enjoyed!

I came to a similar conclusion - a "good" schematic is never enough, a big contribution to a design comes from the layout.

He is a guy.

Its a Hantek DSO5072; but most modern day DSO oscilloscopes have the same functions implemented.

If the near filed noise will be visible in the far field has a lot to do with the casing and the overall device construction. Usually its good practice to measure using far field methods to observe the actual problems and then use near filed to find the sources of the problems on the device; going the other way is not that easy since there is no "threshold" or obvious link.

Thanks. Yes, I agree. Reason I asked is that radiated low frequencies, say 1-100 kHz, are not so easy to measure using an antenna 10 m away.

Do you need actually need to measure radiated emissions at such low frequencies? Anyway, at this frequency most of the radiation will come from the cables connected to the circuit rather than the circuit its self; maybe just magnetic fields coming from some poorly shielded inductors could cause problems.

Hello Dragos! 1 - For analog electronics the main limitation on accuracy (in any simulator) refers to how accurate the simulation model is - how much of the parasitics and non-ideal behaviors are simulated. Also in HF circuits modeling parasitics of the PCB starts to be a problem. For digital electronics, the main issue is getting models that represent the various components - I mean a logic gate is easy to find, but a processor or something similar is a completely different story. 2 - I never used MicroCap but I guess I should try it. In general any spice simulator (LTspice, OrCad Spice, MicroCap etc) should be just as good. Simulation speed might be different based on algorithm implementations but as long as things are set up in the same way, the results should be identical. By setup I don't just mean the simulation circuit and models, I also mean simulator parameters - accuracy, number of digits used, extra default parasitics etc. 3 - Practice. Simulate then build circuits to try and understand how they work. Once you think you understand the circuit, try to improve it - that will confirm correct understanding. Hope this helps! Fesz

In my experience, this will work only under very limited circumstances. You can inject noise into small parts of a circuit using near field probes, but you can't generate noise over the entire circuit usually.

In my experience, the use of near-field probing is to optimize designs on the bench (see if variant A is more noisy than variant B); the other use case is for debugging after a first round of EMC measurements in the lab - for example the unit is generating a spike at whatever frequency, then the exact location on the PCB can be determined using the near-field probe; subsequently any optimizations can evaluated in reference to the initial board. You can make the assumption that if you fail by 10dB and the optimizations you make are reducing noise by more than 10dB at the problem frq you should be fine, but this is very relative. Probing alone will not be enough to ensure that a qualification is passed but it will help to evaluate solutions on the bench rather than in the lab. I don't know what to recommend, it depends on your budget - probes will go from a couple hundred usd to a few thousand.

@@FesZElectronics A great answer as always, Thank you.

Most likely yes; the main advantage of the near field probe is that they will show you the exact emission point - the probe needs to be very close to the noise source to pick it up, otherwise you will not see the spike. The far field measurement picks up the general noise output of the complete unit, with near field probes you can usually localize the exact circuit/component responsible.

@@FesZElectronics thank you for you insight. I did some near field probing recently and came to the conclusion that the FFT on my cheap Rigol scope isn't really up to the task. I'll have to look for a proper spectrum analyzer.

The ones I built, I have no idea, but probably not that much. On the other hand, commercial versions are available that go up to 6GHz or more.

@@FesZElectronics i'm asking in general

I'm not sure if there is a limit. But on one side, with increasing frequency, its more and more difficult to stay in the "near field" - at 6GHz the wavelength is 5cm so the near field ends at around 0.79cm. So its difficult to measure the magnetic and electric fields separately. On the other hand, a 6GHz spectrum analyzer is really expensive, and anything with more BW is even more expensive.

@@FesZElectronics ya now clear about it thank you

@@FesZElectronics is it 0.79cm or 0.79m