Common Mode Current, What is it? (013a)

Common-Mode Current is somewhat mysterious.
To get a grasp on what we are battling, we have to understand what it really is. This is the point of this video as presented to the Great River Amateur Radio Club, Dubuque, IA.
00:05 Introduction
00:20 What has been our experience?
01:24 Terminology
01:56 Balanced/Differential Line?
02:32 What is Common-Mode Current
04:09 How does this work with coax?
05:13 Where does common-mode current flow in our coax?
05:24 Skin Effect
06:17 How many conductors does coax have?
07:23 The Nature of coax and current
09:10 Final Comments and Toodle-oots!

[@W6IWN_Radio]

Thanks for the great information 👍

[@eie_for_you]

You are very welcome!🙂

[@toddanonymous5295]

Excellent presentation Ralph . An old memory of lips Vs microphone was brought back from many years ago .

[@Shastasays]

Hi Ralph love the info. Just put chokes on my UHF/VHF antennas. Will do HF antennas next.

[@rikardlalic7275]

Thank you so much for educating.

[@eie_for_you]

You are very welcome! 🙂

[@ijontichy6070]

Great job Ralph ! greetings from Poland and vy 73 ! - Matt SP3FYI

[@eie_for_you]

I'm so glad you found it helpful! 73!

[@acestudioscouk-Ace-G0ACE]

This helps me a lot. Whenever I heard "outside" I was never sure whether current came along the outside of the shield or the outside of the plastic sheath. If you felt a tingle through the sheath, would this be capacitive? I'm guessing so. Thanks for the video.

[@eie_for_you]

I am glad it helped! 🙂 Yes, if you feel it outside the outside sheath, that would have to be capacitive coupling and a fair amount of current. Ouch!

[@ornithopterindia]

👍

[@alexanderquilty5705]

Loved the video! Anything on Differential Mode Noise...? 😅

[@eie_for_you]

Thanks, man! 🙂 Differential noise is a topic for the DSP folks, I am afraid, as it is part and parcel part of the signal you are trying to hear. I have no plans on going there. 😞

[@alexanderquilty5705]

@@eie_for_you That is fair. I am not sure what your channel is about, but I was trying to learn about CM and DM Noise for PCB Design, since at high frequencies loops in your PCB can form radiating/receiving loop antennas (DMN) and cables attached to poorly terminated/pcb chassis terminations (among other things) can cause that cheeky 3rd co-axial outter conductor to suddenly act like a dipole antenna (CMN) that will also radiate. Regardless, I really appreciated the video! Lucky for me, CM Noise is the harder one of the 2 to understand lol, atleast in the context of PCB Design and how it is created.

[@eie_for_you]

@@alexanderquilty5705 The two rules of thumb I always went by in the PCBs I had to design were (1) "keep traces as short as possible" and (2) "keep analog traces away from digital traces, especially those carrying clock signals." In fact, we had separate ground planes for analog and digital sections of the boards that ONLY met at the common power supply connection ... in ONE place. Thank you for the encouragement and you are very welcome! 🙂

[@jswope6007]

So.... why doesnt the INSIDE of the center conductor count as the 4th ? also, why is the inside flow on the outside, but the shield flows on the inside.

[@eie_for_you]

The insie of the inner conductor is not a surface. The RF wants to conduct itself on the surface of a conductor, not in its core. So, we have two opposing electric fields between the inner conductor and the shield. Thus, because they interact with each other, the currents are on the surfaces which face each other within the coax. Hope this helps. 🙂

[@yjweaver5108]

Good answer

[@Roddy1965]

@@eie_for_you I think the real answer is closer to the fact that the centre conductor interior encloses no free charges, so there cannot be an electric field inside the centre conductor. This is covered by one of Maxwell's equations, I think it's the one that says div E = 0, 'Div' is the upsidedown triangle symbol in math. It's been a long long time since I did electricity and magnetism, but it's a lot closer to reality than what the RF current 'wants' to do.

[@miguelmariopalmieri4058]

Aburridísimo!

[@eie_for_you]

Sorry you feel that way! 😞If the purpose of my videos were entertainment, then I would be concerned. But the purpose of my videos are education and, unfortunately, not all education can be entertaining. If the facts are right and presented in a logical fashion, that is what matters.