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Hi there, we don't expect our audience to be students, but that is great news. We will certainly take your valuable feedback in to account and hope to make more detailed explanation in our future videos. But please also understand, that we cannot satisfy everyone, sometimes, if we make it too detailed, too basics, other people complain, you cannot satisfy everyone, but we will try to keep a good balance. Thanks for your support!

Great questions Sergio, 20 dBohm transfer impedance of the current probes, not ideal for such tests, as the voltage generated will be huge, as you suggested, hence we placed a 20db attenuator, this effective makes the current probe to be 0 dB ohm, meaning for 1 A current, you get 1 Volt voltage. The bandwidth of the RF current probe is important, in this case, the probe is characterised to 1GHz, just enough for the job. We have a series called RF Current probes, detailing everything about RF probes, please review them and let us know your feedback!

@@MachOneDesignEMC Thank you for replying.

To minimise the so-called Electric field coupling. when two cables sit right in the middle, even if you have E field coupling, they should cancel out in theory.

Hi There, I didn't quite get your question. Could you explain it a bit more?

Hi, when we have time, we certainly would like to do a demo on that. Thanks for the suggestion.

Will do

Hi Don, I don't know. The deadline for review is mid January, I think he will be self publishing this book, so a wild guess suggest March or May this year.

@@MachOneDesignEMC is this Dr Todd Hubing?

We will consider launching some videos on those basics, the only reason we don't do such videos is that there are so many good quality videos on the TH-cam channel explaining BW, RBW, etc etc. R&S, for instance, has good videos on TH-cam.

Knowing the level of voltage amplitudes and impedance of the network and device at all frequencies of the range, it is possible to create filters with some accuracy using SPICE.

Also, in one of the videos about 9 tricks for fighting EMS, I wrote a question about 150 pF between the body and power pulsating elements. How to measure this connection and take it into account in filter calculations or what to pay attention to, for example, in high-power frequency converters or 3F inverters, etc. (where massive radiators and palm-sized power transistors are used - 1200 V / 600 A)

th-cam.com/video/Lf51sx6sC0I/w-d-xo.htmlsi=kjH-CaYCynTdu9Cu

1:14:36 time

If we consider DM noise as the integrity of the power supply (PI), the target impedance must be set somehow! For networks, it is in some sense set by norms and standards, and what should we strive for when developing!? The currents at different frequencies are different and even the shape of the graph is unimaginable. How to optimize a DM filter without knowing the RF current level.

Thanks for the feedback, Paul! You know, I have been quite okay solving EMI issues, but for a long time I never understood why we need to do a good EMC Design, until I got a little bit interested in radios. And I can certainly feel your pain, due to the fact that the radio society is shrinking, no one seems to care if radio amateurs complain about the RFI noise in the neighbourhood. But if a 4G tower is down, or the WIFI is disconnected, every one jumps and shouts. I certainly hope we could help reduce the noise of the products we make and give a quiet environment for those who are still passionate about radios. Have a good Christmas, by the way, those Christmas lights are also terrible emitters.

As I always said, perhaps the most useful troubleshooting tool for design engineers. But in the UK, I am quite sad to see most test engineers use RF current probes for testing, without understanding what they do, hence they do not know how to use the current probes for troubleshooting.

Yes, of course. Check the show note to find out the downloadable link. Thanks

Hi Reine, See my reply to Pitti, you got me think hard!

Hi Pitti, again, thanks for your constructive feedback. This really got me scratch my head. The way I see it, first, shielding effectiveness is a wrong word to use in this case, okay, I might have used the word simply to attract more viewers, but I think a better wording for this should be the quality of the co-axial cable. Now moving to your question, it got me thinking hard. Besides shielding quality, it is also cable impedance/mismatch that would influence the result. I could try squeezing the coaxial cable with a clamp or vise, thereby creating a discontinuity of the cable impedance (perhaps somewhere halfway of the cable, if we see a significant difference in the measured spectrum amplitude, mismatch would be important. if not, the result would be determined by the shielding quality. What do you think? Could make a follow up video on it, but I doubt many people would care....

​@@MachOneDesignEMC Sorry did not notice you replied. I'd go with quality, but for me the question is, why do you actually measure current there. From my perspective this can only be CM current and then the question is where does it come from and does the length of the cable affect it? So in my opinion there might be tiny openings in the shield which provide leakage for a displacement current - and while that would be an indicator for the shielding performance one can also amplify this effect by providing a metal plate (good return path) in close proximity like I mentioned. As for the reflections or impedance mismatches you could also experiment with different cable lenghts and clamp positions. Will do some further thinking 😅

Ok .. no new conclusion yet but more ideas: -your comb gen generates a 600ps..1ns long pulse every 1/20MHz (50ns) -in 1ns the pulse travels 20cm (~2/3 c) -it looks like you short cables are 10cm long so parts of the pulse might cancel each other, but there is atleast only one pulse on a perfect cable -if there is impedance mismatch the height of pulse will drop upon reflection, so sth should be visible at the base frequency of 20MHz - however you probably use peak detector so this will not matter IF you measure at a position where the fwd and bwd part of the pulse cannot be at the same time -however you also do not know the exact output inpedance of the comb gen and how well it matches the cable - but probably its ~47Ohm and should not create a big difference So my suggestion would be: -at least 30cm cables -measure at 5..10cm distance from gen output -reflection should not matter due to use of pk detector (here i'd currently have to correct myself, but verify at 20MHz) -still use a metal reference plane at also be more careful on the distances between cables and clamb and positions of items in the setup 😅😅😅

haha James, indeed, just got myself a nice radio receiver, I will see if I can listen to all the ambient signals in my house.

you can certainly use this method, we can look into testing CAT 6 & 7 cables in the future.

You are absolutely right, once the earth wire (E) is removed, we cannot see signals anymore on the scope, because the only return path is disconnected.

Hi, we did demonstrate what is VSWR both from the time and frequency domain in the past, we also demonstrated the 1/4 wavelength antenna in a separate video. I am sure VSWR will have an impact on shielded cable termination, and you are absolutely right, the common mode current will vary depending on the transmission line and ZCM, but we cannot demonstrate everything in one short video. Regardless, your comments are very valid indeed. Thanks

Good shout Julia, I just got myself a tunable dipole antenna, ideal for basic antenna explanations, we hope to make some more RF related video for the upcoming year 2025, thanks for all your kind words and support through this year, we wish you a merry Christmas and a happy new year.

You do not, the 6 dB really reflects the ICM*2 we measured on both wires when we use a current probe. The LISN mate shows ICM.

Thanks a lot

many thanks indeed.

All great advices, I am sure we could make videos on all the points you mentioned, currently we are in the planning stage for next year's video subjects, your suggestions are valuable to us. Thanks

Good questions. I believe it is mostly captive coupling because if both ends are matched then low chances of inductive coupling. It is interesting why the double shielded cable still not doing great job. Maybe the coaxial inside it is not a good quality one. How the current probe terminated to the oscilloscope? 50ohm ?

The braid of the cable is not 100% tight (70% to 90% coverage). So there are openings for the electric field to go through. Then its basically displacement current.. Those terminations typically enclose the load. So if the threads are clean, they should provide excellent coverage. The question for me is actually, how emi proof the scope side is. Some EMC labs have scope boxes/enclosures for ESD verification. Would be interesting to test it with additional shielding.

@@pitti2602 Makes sense, thank you!

50 ohm termination. But also, you know, the noise showing on the scope could also be due to noise coupled directly to the scope, i.e outside of the shielded cable. We cannot easily rule out unless we placed the scope in my tent, actually, saying that, that might be a better test, surely to experiment in the future!

Great question, Krunoslavklaric, shielded cable, if not terminated at all, equals to 0 shielding effectiveness. Terminating at one end provides captive coupling, more like a distributed capacitance bank. When terminating at both ends, shielded cables provide both E and H field shielding. The silver thing is a continuous outershield in this case, inside there will be a centre conductor, it should be made as a transmission line of 50 ohm to match the co-axial cable, but good point, I should have checked whether this silver connection is a 50 ohm structure. Thanks for your comment.

Can I actually use a current probe to measure DM current in 100s of Amperes? I suppose yes, but that leads to the above problem.

good question Mustaf, most likely the probe will saturate, I am sure some manufacturers can have a design to improve their current rating, but that often at a cost. Also, for such probes, you will probably not get 1 ohm as transfer impedance, they are most likely like 0.01 ohm or something like that.

actually, I just looked it up, Tekbox will soon have one probe that is capable of taking bias current up to 200 A without getting saturated, and the transfer impedance is about 11 dbohm, but they also recommend only use the probe to measure RF noise, the current rating is really there to ensure the probe does not get saturated. So I guess if you want to use a probe to measure accurately on DC to a few hundred hertz, best is to use a Hall effect based probe.

correct, it is the outer shield we tested. between the centre conductor and the shield is the 50 ohm terminator resistor on one side, on the other side is also a 50 ohm impedance (of the oscilloscope), so we have a close to ideal 50 ohm transmission line, in a sense that the source is 50 ohm, the transmission line is 50 ohm and the load is also 50 ohm.

For business inquiries, you can. But as you can imagine, we are dealing with hundreds of emails every day. Like TH-cam, we try to answer all the questions as much as we can. Thank you for your support.

Typically, I find, at least for EMC work, the unshielded probes work just as well as the shielded ones. The highest frequency I used for troubleshooting EMI work is about 1.3 GHz. If you check Langer EMV, they always characterise their probes to a few GHz. I am sure one can use these probes for measuring emissions on a small chip or something, but that is something I have not come across, yet.