nanoVNA - What does a 1:1 current balun do? (TEM - Transverse Electromagnetic Wave theory) - Ver. 3

What does a common mode choke or 1:1 current balun do?
------------
Note - September 2023
Even though this is my third attempt at presenting this material, I still feel there are things to improve.. for instance, the ends of a dipole antenna don’t go to ground. They are the point at which maximum voltage exists.. but I wasn’t sure how to depict the antenna and the resistor circuit I drew in such a way that the relationship (in concept) could be easily seen.
I may re-do this video again in the future if I’m able to come up with better ways to explain a few things. For instance, rather than using an awkwardly presented lumped element model for the antenna (with the ends shown going to ground) I may try to present it using a distributed element model.
------------
Original Notes:
This is my third try on this subject. I took about a month to research the material and to make notes so that I could try to do a good job on presenting the information. I also tried my best to ensure that the information is accurate and also accurately presented.
This is a non-mathematical attempt at explaining some fairly complex material... that being said, if you have first hand experience with this subject material as an engineer or perhaps as a professor and have some comments regarding my presentation, please feel free to contact me.
Some of this material is newly discovered for me, and I did learn some interesting things while researching this video. I hope you find the information presented here to be as interesting as I did!
How to build a current balun (common mode choke):
1. vk6ysf.com/balun_choke_balun_...
2. kzbin.infoUgkx5stRzvpF...
3. www.pa9x.com/the-broadband-co...
4. noji.com/hamradio/pdf-ppt/noj...
0:00 Intro.
0:42 Installing a new dipole antenna mount.
1:52 Using the nanoVNA to examine the new dipole (no balun installed).
3:09 Back to the DG0SA current balun. On the test bench with the oscilloscope.
3:47 Unbalanced vs balanced signals on the oscilloscope.
4:04 Leadup to explaining how the balun works and why we need one.
4:40 Falling down the rabbit hole... more coffee needed!
5:43 The start of figuring it all out... a blank piece of graph paper. Haha!
6:14 The basic radio system.
7:02 Introducing - The coax cable!
7:41 The energy propagating down a coaxial cable is present in the dielectric?
8:00 Introducing the TEM wave.
8:56 The movement of an electric field causes the magnetic field to exist.
9:16 The RF energy carried along a coaxial cable is done so by the electromagnetic wave, which exists in the dielectric.
9:49 Taking a closer look at the end section of a piece of coaxial cable.
10:33 The electric and magnetic fields cause voltages and currents to be present along the conducting surfaces within the coaxial cable.
11:24 The inner shield and outer shield are two separate conductors.
11:59 Charge and current densities formed along the conductors by the TEM wave.
13:07 Illustration of the cross section of a coaxial cable. E and H fields. Right hand rule.
13:52 Roy Lewallen W7EL - Article on baluns and circuit diagram of currents on a coax.
14:27 "RF Transmission Lines" - Department of the Army Technical Manual (TM 11-675)
16:00 Currents flow along the inside and outside of the coax shield.
16:46 When the TEM wave arrives at the antenna end of the coax cable...
17:13 Kirchoff's current law.
20:00 The consequences of KCL...
22:05 What strategy to use to eliminate common mode currents from the outside of the coax shield?
23:36 The common mode choke (current balun).
25:39 Using the right hand rule to look at a common mode choke built from RG-58 coax.
27:07 Two types of common mode chokes that work. Introduction to the DG0SA current balun.
28:38 Final comments.
References:
www.microwaves101.com/uploads...
myantennas.com/wp/tech-info/a...
upload.wikimedia.org/wikipedi...
gm3sek.files.wordpress.com/20...
www.engr.newpaltz.edu/~zunoubm...
ham.stackexchange.com/questio...
vk6ysf.com/balun_choke_balun_...
www.eznec.com/Amateur/Article...
www.microwaves101.com/encyclo...
rfcec.com/RFCEC/Section-3 - Fundamentals of RF Communication-Electronics/27 - RF FEEDLINE/RF Feedline - What makes a RF Feedline Balanced or Unbalanced (By Larry E. Gugle K4RFE).pdf
www.nj7p.info/Manuals/PDFs/Mi... 11-675 21-Aug-51 NJ7P.pdf
VE6WGM (VE6WO)

[@richardwesterman5773]

EXCELLENT video, Greg. THIS should be mandatory viewing for all hams. TNX and 73 de DJ0IP.

[@ve6wo]

Thank you.

[@neilhankey2514]

Until now I have never seen someone get this exactly right. Thank you for the video. Keep up the great work.

[@ve6wo]

Thank you for the kind words.

[@2013Davey]

Fantastic explanation .... thank you

[@Simon-mz7sf]

Thankyou. You really clear the forest from the trees in your approach to explaining things. Appreciated

[@IZ0MTW]

Your work on the subject is remarkable. As said on another comment should be mandatory to the ham operator ti understand these concepts. Keep up doing great videos, I’m watching the others. Congratulations and 73. Diego

[@ve6wo]

Thank you for the kind words.

[@MicheIIePucca]

Finally... someone from Alberta on KZbin :)

[@ve6wo]

Yessir! :-)

[@MicheIIePucca]

@@ve6wo I did cheat though and did a call sign lookup.

[@ve6wo]

No harm in that. I usually have QRZ up on a screen while I’m playing radio so I can see where signals are coming from. Gives me an idea of band openings and where I can hope to communicate to.

[@KilianGosewisch]

i am currently getting into ham and had a bunch on previous "engineering" and electronics knowledge from previous hobbies and many things did not make sense to me. for example how people throw around the word balun and how it is often interchangeably used with choke etc. this video cleared up a lot and prooved and i am not stupid ;) thank you very much!

[@ve6wo]

You’re welcome :-)

[@ve3dvy]

Wow. I have yet to see an explanation this well done. And thank for providing your refferences. This qualifies this video. If OK I will be using it as extra study when we start Basic classes. Thanks!!! VE3SD

[@ve6wo]

Yes, please use the video :-)

[@DarkoObretan]

Current on the outside can flow only because of miss-match or imbalance of left and right dipole. Current inside coaxial cable is by definition equal and opposite (I1=-I2) and even if impedance of coax outside would be 0, there would not be any current flow outside of the coaxial cable if dipole would be balanced. (Which it can't be if using coax, because both dipole sides are having some capacitance to nearby coax shield, but voltage polarity is opposite, so they see different impedance, and that's why there is unbalance in current flow). (Dipole in practice also have different distance to nearby trees, buildings and that also affects it's balance...)

[@ve6wo]

At the end of the coax where the antenna connects will be two paths for current to flow. One will be on the leg of the dipole, the other will be on the outside of the coax shield. Even with a perfectly balanced antenna, this is still true. The result will be that some current will always be present on the outside of the coax, no matter how perfect the antenna is. The best way to minimize current on the coax shield, and maximize current on the antenna is to install a common mode choke at the antenna feedpoint to present a high impedance to currents that would otherwise flow along the coax shield.

[@DarkoObretan]

@@ve6wo Yes, I agree with everything, I was just bothered with what you said at 20 minutes (that current on the outside flows, no matter how well matched antenna is. Maybe it was misunderstanding from my side, because I understood matching also as 'how balanced antenna is' on the feed point).

[@phystimn]

That's all a pretty nice explanation of the currents on 'inner' and 'outer' surfaces of the shield. However, wouldn't it be just more persuadive to organize an experiment (using nanoVNA or similar device for example) to demonstrate that the currents indeed flow in the described manner and that the balun indeed changes how do they flow? After all, the purely engineering objection to the given explanation could be that the shield is made up of individual wires, it has multiple 'holes', so that many connections between its inner and outer surfaces exist.

[@ve6wo]

I was just recently thinking about this.. a person could use a clamp on RF current meter to demonstrate physically.