Thanks!

Your welcome! Glad I solved that mystery!

@@ElectromagneticVideos you're* :(

@@NoNameAtAll2 Do you have some videos?

@@NoNameAtAll2 god not the grammer not zee. Math and physics is his thing. We are not here for the spelling content!

@@rwood1995 I can’t imagine how you native english speakers can mix up your and you’re. I know it’s pronounced the same, but with a bit of logic you can differentiate them.

Thank you so much! I was really trying to do it without the math to make it understandable to almost anyone.

I so appreciate your comment - thanks! I'm quite thrilled at how well this approach to explaining it has worked for so many viewers. I did a very similar experiment in a lab as a student and its one of the very few that I was so taken with I have always remebered. It was great fun to do it again after so many years. More things like this to come - mirrors, reflections from transparent objects like glass, speed of light ... . All with as simple equipment as possible.

Yeah, I loved that bit.

Thanks - I really appreciate that! I was so lucky to have a number of great EM Profs when I was a student and thats where I got that intuitive approach from.

Your welcome! For what its worth I did my share of thinnet way back as well. Seemed so fast back then when files were small :)

So glad it helped understand impedance matching. Since you are getting in to amateur radio, consider getting a NanoVNA. For about $100 this amazing devices does the job of what used to be a multi-thousand $ piece of test equipment. It great for measuring impedance of things like antennas, determining SWR at various frequencies etc. It really brings all that stuff to life!

Thank you so much! Welcome abord to EM Videos!

What cool hobby - something I always think I should get into when I have time. I have done long range digital HF communications at work in the past - quite amazing the distance that can be achieved even just a few hundred watts if the conditions are right. Just so that anyone reading this understands, while my example was 75 Ohms, what I did also applies to 50 Ohm cable or any other characteristic impedance cable. At some point I will cover SWR and quarter wave transformers to match different impedance's which is also pretty neat and related to this. Look it up if you haven't already! Thanks for the comment!

Well I'm glad you liked it and found it informative. In terms of loosing the higher frequency harmonics, for a well matched/terminated system, the cause is the changing characteristics of the components of the cable. That includes the insulation plastic between the center and outer conductor becoming more RF absorbing at higher frequencies, , and the increasing effects of skin depth making the conductors more and more restive as the frequencies go up. That being said, many cables today commonly used in our or wireless devices work remarkably well in the GHz region although the spec sheets generally show the loss/distance increasing with frequency.

Thank you so much! I really appreciate it!

Thanks so much! I'm glad you found my way of explain easy to understand - certainly what I try and do!

Thanks! Keeping things simple was hat I was trying to do!

​@@ElectromagneticVideos I think your 2ch HP scope is quite fancy 😊

@@sophya5796 Actually it is even for a 25 year old scope! I specifically bought it (used) a few years ago troubleshoot some glitches on an i2c bus - it did a wonderful job on that and many other things. Something like a 100MHz analong scope would be fine for this demo. Or slower with a longer cable.

Thanks! I'm so pleased the video helped provide an explanation of reelections and characteristic impedance.

Thanks! Actually the video was inspired by a lab a million years ago whne I was an undergrad. I always thought that lab was an eye opener!

@@ElectromagneticVideos come to think of it, I just took a class where we did a very similar demo. Since the class was online though, the voltage waves were simulated in Matlab’s Simulink. If you have any more demos from a million years ago, I’d love to see them!

@@kurtttttttt More million year old demos to come :) It get having to use simulations for online courses, but I always feel you get a better sense of things with real experiemnts. And they are more fun!

Your welcome! Yes! Its a lot harder to justify the nuisance of a splitter without the "why".

Glad you found it useful! What I remember about the university lab we almost always did the lab before the theory which was too bad in terms of understanding it. You know, if your setup works, I wouldn't go to the effort to change the connection to a splitter... "dont fix it if it aint broke" :)

Thanks! I'm so glad it was useful and answered a few things.

Your welcome! Glad you found the fundamentals behind things like impedance and termination interesting!

Thank you so much! If you want an incredibly cheap but capable tool for that sort of thing, look at the Nano VNA if you havnet already seen it - does smith charts, measures RF impedance etc, all at a cost of about $100 or so. There are numerous variants of it available - I got one that was in $150 range - larger screen and up to 3GHz operation - best RF toy ever!

Glad you liked it. A warning thought - different cables have different impedance. 50 Ohms is also very common, so you have to make sure you are using the right value terminator.

Your welcome! Yes - thin and thick Ethernet and other obsolete lans from the old days!

Thanks! Apreciate that!!!

Very nicely stated. I will add you can get non-resistive splitters generally with limited bandwidth that do a very good job of both impedance matching and transferring close to have the signal power to each of the two outputs.

Well thank you Mike! I'm glad that somehow the way I presented it worked for you. The video was based on a lab experiment I did as student and I have never forgotten it. Hopefully soon something similar with light ...

Wow - thank you so much! High-Speed PCB design - I should actually dig out one particular circuit board from years ago where I designed a couple of long impedance controlled transmission line traces for 100Mbps twisted pair Ethernet which is a great example of transmission lines on circuit boards.

That made my day! This was a reduced version of a lab I did as an undergrad. If you want to make it more challenging, non-resistive loads (capacitor or inductor) can be used at the end of the lab. I think we even had to identify the contents of some mystery loads.

@@ElectromagneticVideos I stress the concept of Max Power Transfer beginning on the first day of the course. These are technology students, so not sure how they would do with the reactive dummy loads, but will consider it. I would also look to have them identify the impedance of other cables (twin lead -300ohm, and come 50ohm coax) to validate the method. This brings home that the concept of line impedance is really and not something made up. I also like the time-domain measurements that brings home the concept of matching and reflection as it relates to open and shorted lines. Last thing, I'm curious if given enough of cable run, could the students also identify the velocity factor for a specific cable?

Thanks so much! Glad my explanation was helpful!

So glad you found it so interesting! It is really stuff!

Thanks you so much! Glad to be able to shed some light on it for you!

Thanks! Cool that you actually used it!

Thanks you so much!

Thanks so much!

"The break is usually in the vacinity of a completely oblivious plumber or domestic electrician" oh that's so funny! And I don't doubt it for a moment.

Plumbers make sure that electricians have jobs.

@@jannejohansson3383 :)

Got to love those. We had similar problems with crushed flexible waveguide sections on B-52s from crew chiefs (usually) standing or climbing on them. All of them were marked in day-glo yellow paint "NO STEP". You would think that would be easy to read.

Thanks! I was fortunate to have great profs in the subject who explained it to me!

"it's always good to get a new explanation. You never know when something new might click." How true!!!!! I know for me often one explanation really give me a sense of how something works, and another (equally good one) may not click with me.

​@@ElectromagneticVideos❤

Glad you liked it. Certainly keeping reflections to a minimum will help with both receive and transmit powers!

I'm sure old cable wiring with unterminated splices drives cable company installers nuts when they try and get cable modems going!

Thank you! I'm glad you found my explaining worked - I always find that with each of us havinig a slightly different prespective on things, sometimes one or another explanation works best. The veritassium poynting vector one? Its another neat look at similar stuff - a bit missleading but that may just be my perspective. I am actually thinking of recreating it with an experiment. Course being a small channel I cant afford 300,000 km of transmission line so it will be more like 300 feet :)

Your welcome! Glad you felt seeing the video was worthwhile!

I remember the one you probably thinking of, If must have sold and hopefully found a good home. This is a much more modern one - only 25 years old!

Thanks! Just threw 50 Ohms and 75 Ohms into the reflection equation and the mismatch results in a 20% voltage reflection. Not a huge amount, but enough to loose signal power and smear things if a mismatch on each end of the cable.

Thank you so much! Its always a challenge to explain a mathematically intensive topic in an intuitive way with minimal math - I'm thrilled to apparently have succeeded!

Thanks! I hope by amazing you mean amazingly simple. Should be easily duplicated at home or in a classroom with relatively inexpensive equipment.

Thanks! Glad it helped!

Thanks! That part was to show that if you just splice cables together, it looks like two resistors in parallel = half the impedance and you get a reflection. So you need an impedance matching device like a splitter sending the signal to two TVs for example.

Glad you enjoyed it! You must be taking a 2nd or 3rd year EM course - those were some of my favorite courses ever. Good luck on the exam!!!!!

Thanks yo so much!

Thank you!

Thank you so much! Glad you liked it!

So how obvious were things like kinks? Did the cable really have to be bent to show up?

@@ElectromagneticVideos Depends on the sensitivity of the instrument. We used a USM-430 TDR in the military that when properly calibrated could be used to located impedance changes as low as 10% of the nominal value. Larger discontinuities generated larger return pulses on the CRT display. It was also capable of measuring phase shift within .1 degree if memory serves, and we used that function to check the phase matched RF cables between the receivers and processor on the F-4G.

@@ElectromagneticVideos Yes, bends would show up as changes in impedance. It was pretty usable, it had a scope/screen, but also an option to printout a ribbon of thermal paper with length graduations along it. Every 2 1/2 meters, if a vampire tap/connector was present, there'd be a little blip. A sloppily performed tap may short, effectively ending the cable as for as the TDR would sense (as I recall, any signal traveling beyond the short or it's echo would be eliminated by the short). Distance to a node does have limited value. A story I can share is of a Sun OS "pizza box" (pre Slowaris) was recycled as a licence manager for a large distributed CAD site. IT lost track of were the little box was and when it was time to rebuild the Kernel, they tried to find it to no avail. Fearing bringing the LMS down and not being able to bring I back up the machine ran for well over 400 days before a custodian found "an old computer" hidden above a closet on a drop ceiling panel. Of course, a TDR doesn't tell you the MAC or IP of anything on a cable, just reflected signals/reactance.

@@RobertLBarnard So print a measing tape - that something I have never heard of. Interesting about taps going bad. I didnt come across that with thin ethernet but sometimes a cable connector would come off - either from the cable or the BNC not being attached properly. I have a bunch of BNC Ts from the old networking days - will have to see what type of reflections they produce whne attached to an old network card. A Sun hidden in a drop ceiling - thats a new one! I remeber those pizza boxes well - whne I was a grad student Sun was the standard workstation in our lab. How great they seemed back then and years ahead of PCs in terms of performance and a window system - wasnt the window sustem SunView. And and pre solaris their unix was SunOS.

What a wonderful complement! Thank you so much!

@@ElectromagneticVideos :)

Thanks! Really appreciate your comment!

Thanks. So the glass reflection video will be from the classic EM standpoint: how the only solution to an EM wave at a surface dufferent impedance is some being reflected and some going though. Your photon question goes into quantum physis: Here is the very short explanation: Each photon has a wave function with highest value were it is most likly to be any point in time and space. The highest values are wher we expect it would go with classic physiscs. The wave funtion includes a complex terms (e to the iwy + theta) which carries the wave properties in terms of wavelength and phase. These probability wave funtions interact with the sheet of electrons in the metal mirror. Your could think of everry point on the mirror reradiating a probability wave with a phase releated to the phase of the impinging probability wave. And whne you sum it all, you end up with the highest probabilities along where we would expect the relfect ray/phototn to be. Put a gazillion photons together and all the tiny controbutions from each photon add to a very stable average to become the EM fields we are used to. So thats the verys quick handwaving answer that is intented to give a sense of whats happening as opposed to rigerous physics. Hpe that helps!

@@ElectromagneticVideos Thank you very much. I appreciate the clarity of your explanation.

Thank you! I have always loved combining theory with actual real stuff - it really brings it to life!

I am so honored to have received so many comments like yours. Its funny - I was rushed doing the video and its certainly not the quality I wanted it to be and never would have guessed it would get the attention that it did. It is based on a 2nd or 3rd year lab experiment I did as a student decades ago. My challenge in this video was to try and show how transmission lines works without the math - I'm thrilled that I seem to have succeeded! Thanks so much for the kind comment!

Thank you so much - really appreciate your comment. Have you ever used it for non-RF cable? I have wondered how well it works with cable not designed or installed with constant impedance in mind.

@@ElectromagneticVideos I haven't but if I remember correctly, ethernet cabling has effective 100 ohms impedance and that's the most commonly used cable for such tests. I would expect that you can measure any cable type as long as you can tune the signal generator: you only need steps in the signal. The speed of light is always close enough to 1.0c that you get distances roughly correct without knowing the true impedance. And since the sign of the voltage is enough to separate broken wire from shorted wire, that's good enough, too, without knowing the true impedance.

@@MikkoRantalainen Your right about the Ethernet cable! I should really experiment with some 14/2 house wire - I wonder what its impedance is (should be easy to measure) and how constant it is when it is near other cables since it has no shield or twist.

@@ElectromagneticVideos house wire is intended for very low frequencies (50-60 hz), so no thought is given to impedance. More interesting would be twisted pair cables used for lighting systems (DMX).

@@TomCee53 Just looked up DMX. Looks like its similar or even repurposed RS-485 so maybe 120 Ohm cable?

Well thank you! Nothing better than the explanation being called excellent!

Well thank you! Glad my way of explaining works for you!

"not intensely enough to wade into div/grad/curl" :) Actually the neat thing is you can do the transmission line math with plain old differental equations becuase its really a one dimensional object from the wave standpoint. Butther eis nothing like seeing a real experiment to understand as you said. Glad you liked it and welcome to my videos!

Thanks!

Thank you so much! Glad you found it useful. I`m complelty fine with any instructors playing the video to a class or distributing the link so if you would like to suggest it to the instructor, or suggest an in class demo is done based on the video, please feel free to do so. Any number of free online UKposts video downloaders could be used to ge the video file so a class does not get subjected to the ads that are normally inserted.

Thank you so much! I was actually wondering if I could do it with minimal math too - pleased tio have been largely sucessful!

Glad you found it useful! Its funny/sad how different instructors can taint ones understanding and enjoyment of a subject. I had the best profs for EM and ended up loving it. I had the worst prof for control theory - to this day I dont much care for the topic, but at least I have finally gotten a decent understanding of it over the years.

Sorry to hear it took that long :) Glad to hear that seeing this video helped!

Glad you found it easy! Actually fibre is more similar to coax than may be obvious. The speed of light in glass is ususally 2/3 that of light in free space, so similar to the coax and for the same reasons! And, optical fibers do have bandwidth limitations too, but at the much higher frequencies of light, bandwidth is so huge its mush less restricting. And - relfections at the ends and matching impedance to prevent loss of optical power is all the same stuff just done with glass or other transparent materials. I have a few videos planned with all of that stuff - stay tuned!

Thanks you so much! I just subscribed to your channel - looks wonderful - too bad I don't speak Italian but hopefully the UKposts captions translation function will work! Greetings from Canada!

Thank you so much for that comment and what a wonderful way of describing it : "waltz of mathematics and physics". Thats such a great way of talking about electromagnetics - the intertwining of electric and magnetic fields to give us everything from light and radio waves to reflections in a transmission line. More of this type of stuff to come!

Thank you so much! Just so you know, I try to do a video a week but like right now, work or other things occasonally gets in the way. I do have one more video almost edited - with luck I'll get it up before I get back home. Thanks for subscribing!

Thanks! Nice to hear it was "easy to watch"!

Your comment made my day! Thank you! Yes it is amazing - the thing that I found most amazing when I was studying it as a student was how you can measure static non-moving electric and magentic field characteristics and from that get the speed of light. And how light is just and electric and magnetic field - wounderfully amazing. And I will do a videe on that sometime!

It is such a nice, simple to to do experiment its too bad it isn't done more often.

Yes! I didnt go there because I wanted a visual way to show people reflections rather that having to explain standing waves. I will probbaly do something with standing waves or interference patters soon.

Thanks you for that wonderful compliment!

Thank you!111

Wel thank you so much! "Easier to understand than what it really is" well maybe easier to understand that with the full blown math? Even with the math I find a good experiment like this really helps me undertand what going on.

Thanks! The twisted pairs video is delayed - had to go on a suddden business trip. Back in 10 days so should be able to get back to videos!

Your welcome from the other side of the planet - Canada!

@@ElectromagneticVideos Thanks ..... Appreciate your reply .... I am into CB / Ham type Radios and love building Antennas and Your Expanation just 'Hit the Spot' .... Best to You and Yours from ChCh, NZ

@@kiweekeith Thanks again - glad the explanation 'Hit the Spot' . Its really neat stuff - I'm an EE and this sort of stuff is covered in the EM fields and waves courses in university which I always liked. One of these days I'm going to get a Ham license - what a neat hobby!

Well thank you! So glad I help you understand it a bit better!

@@ElectromagneticVideos What is the resistance of the resistor (-network) you used on the input side? Is that 75Ω?

@@FrankBitterlich So most signal generators are 50 Ohm outputs. The TV coax I used was 75 Ohms. To make them both see the right load, I used a 10 Ohm resistor to ground. The Signal generator was connected to that resistor though a 39 Ohm resistor so it would see about 49 Ohms (close enough). The coax was connected to the 10 Ohm resistor with a 68 Ohm resistor so it would see 78 Ohms, close enough to the 75 Ohm Characteristic impedance. Note that I am assuming the 10 Ohm resistor is so low compared to the others that any effects of the resistors on the other legs can be ignored. If you use some 50 Ohm cable - almost any cable other than TV - and a 50 Ohm signal generator - you don't need the matching network.

Thanks!!!!!!

Thanks!

It is neat experiment. If you want to try someting intersting, try a variabe resistor at the end of the line. As you turn it you can see the refelction go from positive to none to negative. One thing I didnt try was watching thereflections as really sharp bend is made or the line is crunched with pliers - might be interresting to look at.

@@ElectromagneticVideos Yeah! I was thinking of trying a ganged 10-turn linear pot. So that you have two variable resistors that are pretty well matched on each end of the cable. Definitely, or what it'd look like if you have a 50-ohm coupler between two 75 ohm cables. Would something as tiny as a mismatched coupler show on a scope? Fun stuff!

@@button-puncher The other thing to try is capacitors inductors or some RLC combination at the end. That was part of the undergrad lab where I first came across the experiment as a student. We had mystery loads that we had figure out by looking at the reflections. Probably really tough for those who did the lab before the theory was covered in class (There were a bunch of different experiments. Each lab group did a differnt ine each week, so they werent always timed well with the lectures).

Thanks! Appreciate the compliment!

Thanks! You could be right. I looked up the cable I used and it was 0.8 . There were others listed at 0.66 and some as high as 0.92 (that may have have been 50 Ohm).

Genius? Hardly! But much appreciate the comment. Thanks!

You know, I'm really amazed some variant of this wasnt done in demos or labs for the appropriate classes You may have read my other replies - this video was inspired by a lab I did as a stundent.

Yes - its old and and wonderfully simple and mechanically rugged hardware store multi-meter. Sadly many of the more recent ones are so filled with functions that its a nuisance. I have one recent one that has a wonderful of array of functions but DC voltage is not on the dial switch. Voltage defaults to AC and you have to press another button. Almost like designed by someone who has never used one!

Thank you - really appreciate that! Here is a copy and past of a previous discussion that describes the impedance matching network in more detail than you probably need, but will be useful for anyone reading this: Most signal generators are 50 Ohm outputs. The TV coax I used was 75 Ohms. To make them both see the right load, I used a 10 Ohm resistor to ground. The Signal generator was connected to that resistor though a 39 Ohm resistor so it would see about 49 Ohms (close enough). The coax was connected to the 10 Ohm resistor with a 68 Ohm resistor so it would see 78 Ohms, close enough to the 75 Ohm Characteristic impedance. Note that the 10 Ohm resistor is so low compared to the others that an effects of the resistors on the other legs can be ignored. If you use some 50 Ohm cable - almost any cable other than TV - you dont need the matching network.

Your welcome! Glad you liked it!

Thanks - glad you liked it. It was actually inspired by a lab in an EM course I took as a student years ago. The main difference was I tried to explain it with minimal math in the video.

Yes! I didnt get into this but the trick is to use connector caps that have 75 Ohm loads built into them prevent reflections. The reflections are actually worse than this video shows when there are multiple improperly matched connections or unterminated ends - when the cable distances between those ends is multiples of the wavelength of a particular frequency. the signal at that frequency can be completely wiped out due to destructive interference or greatly enhanced due to constructive interference. This results in all sorts of weird effects. This is actually used to make some RF filters. The real cost saving use is of course to find the location of faults in things like buried cables. And of course, if you take away the transmission line and replace it with an antenna, its RADAR.

Thanks you verry much!

Thanks!

Thanks. So glad you found it interesting!

So glad you liked it! It was inspired by a time domain reflectometry lab in an EM course I took as an undergrad in university. I never forgot that lab experiment and am thrilled so many people enjoyed this video.

Thanks you and I will keep doing them. I do put out videos in spurts depening on how much free time I have. A number of other ones already in the planning stage.

Wonderful!

You know I often wonder what things would have been like for me if all the internet resources were available. On the one hand the weath of resources we have today making understanding stuff so much easier. But then the constant distraction students have with messaging etc. And yes - the price of equipment and parts was such a killer. I used to go out on large item garbage day and pick up things like old TVs and radios and strip them of parts like resistors and capacitors. Restors now cost 100 for $1 or better!. Just searched w2aew and found it and subscribed. Thanks for pointing it out to me!

Yeah but if you were born 30 years later you wouldn't know what good music sounds like. Or good movies.

@@johnclawed Ha! Yes!!!

Thanks! I appreciate that!