My dad worked at Bell Lsbs and I had a basement full of test gear and jars of vintage transistors to toy with as a kid, and consequently have always had electronics and radio close to my heart and am still learning the deeper aspects of those subjects. Bell Labs was an amazing place, there were actually two, one in Murry Hill, NJ, where the transistor was invented, and one in Holmdel, NJ, where my father had worked and did quite a bit of transmission cable work and later fiber work. There was a white water tower there at the campus in Holmdel with 3 support columns, which oooked suspiciously like an oversized transistor; the joke was someday someone would paint E, B, and C for emitter, base, and collector on the bottom of the tower to properly label the “leads” of the water tower. That kind of research is where it’s at, we need to get back to that collaborative multidisciplinary approach with a big center and a big budget to push the technology frontiers hard again. For example, the west needs workable fusion power, and the fragmented approach is perhaps costing more in lost time, than it is saving in dollars.
Maybe this has been commented earlier in this thread… About 5:30 into the film, John Shive talks about the termination of an electrical transmission line. At first, I thought John Shive was wrong, since I have truly seen the opposite in our lab. What I have seen on an oscilloscope is a wave that returns “upside down” from a short circuit termination, while an open circuit termination gives a reflected wave with the same phase as the incoming wave. But John Shive talks about a current while an oscilloscope measures voltage. At an open end, the law of conservation of energy results in the pulse having to return to where it came from (since it has nowhere else to go). Going back, a current would have to pass through an imaginary amperemeter in the opposite direction compared to its original direction, thus giving a current with the opposite sign. So, John Shive was right about the current. Why doesn’t the voltage change polarity as well? This also has to do with energy. The termination and the ideal wires do not “steal” (convert) or store any energy. Therefore, the sum of energy from the forward and the return wave must be zero, E(forward) + E(return) = 0 and E(forward) = -E(return). The minus-sign comes from the inverted current, therefor the voltage can’t be inverted. Anyone who agree with me?
I had the same initial thought, about shorts vs opens, but just figured I had misremembered my EM classes, since the professor must be right. Thank you so much for explaining the mental disconnect. I'll sleep better, now that Dr shive and I agree.
Well if energy stored as torque is analogous to current and amplitude displacement is analogous to voltage, then your initial impression I think correct. Analogies between different media only go so far. As an RF engineer as you are probably also we have seen any resistive load above the characteristic Z of the line return a reflection in the same as the incident polarity, while a lower R returns an inverted one.
Amazing. So clear and direct. I find the further I go back in history, recorded science lectures seem to just make way more sense than today's classes. I'm not sure why. Maybe they weren't trying to teach so much at once then, and they had a script, so the material was presented in a very logical order, but this is definitely easier to understand for me than a lot of more modern videos that seem to just "wing it".
Agree. These basic videos are explained step-by-step with the goal of understanding.... Today's videos seem to focus on flashy presentations but lack clear instruction...
A lot of them (military analog computers comes to mind) had a very interesting non academic, non ceremonious yet charmingly vintage in style. Probably as good as a MOOC :p
The explanation's rather simple I believe: it's laziness. It takes real effort - persistence, thoroughness, time - to produce instruction of this quality. That's been replaced all too widely by superficiality, glitz and the desire to be considered clever without the requisite work to become clever. What's one of the most common complaints about RU-vid tutorials? Too much attention paid to background music. Dr Shive's teaching is devoid of such frills - and brimming with evidence that he really knew what he was talking about and went to considerable lengths to communicate it effectively. The same's true, for example, of w2aew's RU-vid videos and content from the Khan Academy. There are no shortcuts to excellence.
I truly appreciate that you have this video available on RU-vid. It is probably the best demonstration of wave theory, reflected waves, impedance matching & SWR that I have came across. Please Never Delete this Video 🙏💜🙏
I wish I would have had someone like him when I was studying to get my Amateur Radio license, I might have accidentally learned something instead of just memorizing the correct answer.
This is gold. I am amazed how the concept of impedance can be applied to so many things at once and how waves are all similar in their nature. I went from having no deep understanding of waves to seieng patterns between different physics areas in one video.
I remember teachers like this as a child, pleasant, refined, disciplined, and often very conservative. They did not suffer fools lightly. It is a sad reality that the ability to calculate in mathematical terms is extremely difficult for so many people. The best way to counter this condition is through constant repetition. Practice practice practice from a young age, as soon as possible. The torture of that exercise will pay huge dividends later in school. So many geniuses become lost in this struggle, the old left brain right brain argument. Matching the imaginative dreamy brain with the analytical is another form of impedance resulting in miraculous new innovation. Happens every time.
Repetition may help to memorize but what's generally missing in the first place is meaning. There is a generalized use of mathematics in a meaningless approach. That may be the bigger problem. Meaning may though depend on earlier non symbolic early experiences... Diffcult subject! They are many discussion in this direction in Education in Mathematics but this subject of research is not in an very advanced stage.
Its funny how entitled Incels who think they're better than everyone else spread to every corner of the internet event the education part 🙄 This comment shows a clear lack of understanding how social systems generate behavior.
Wow-- what a terrific explanation. Every instructor could learn from his relaxed but deliberate pacing-- gives the student a moment to reflect on what he's saying. For anyone wanting to learn more about what an amazing place Bell Labs was, I really enjoyed Jon Gertner's book.
Love the use of big fractions fractions at around 18:35. When I was in school, oh so long ago it seemed perfectly intuitive for me to use =>1 fractions. I was told that this was wrong, somehow -- though my work was accurate, correct, documented, and mostly legible, I tended to skip the needless reduction of fractions at every step that they expected it of me. Conferences were held, admonishment was dolled. I now feel vindicated by this verification that there is no shame in expressing a number as "seven halves," as everything presented in this film is perfectly cromulent and expertly explained. Thank you.
@@tarmil Know this is old, but your observation makes sense. We Americans use the imperial system, so ''improper'' fractions have a good deal of practical use to us.
Ditto, Adam Perry...loads of arguments and discussions with mathematics teachers in high school. But the methods taught to me by my engineer father worked best for me! As long as my answers were correct in the end....
Fantastic video! Wave behavior mathematics are difficult to learn at the beginning, and it's not clear what is physically happening in, for example, radio or AC transmission, and why impedance matching is so important. This video makes the reason that is important and how it works clear. I love it!
At 05:09, I think that load impedance is not correct: positive reflection happens on open circuit (not short circuit), and negative reflection happens on short circuit (not open circuit).
He should explain it with regards to Voltage (not Current). I.e a short circuits does not allow the voltage to change (fixed side), whereas the open circuit allows the voltage to change (open side).
this channel has become one of my favorites on all of RU-vid, and why youtube is so amazing. i'm one of those math-challenged liberal arts majors (lol right) but i found the UNIX video *really* cool as a backgrounder on computer science in general as well as UNIX, coding etc etc. this vid is incredibly educational as well. awesome stuff, ATT.
Brings back memories of the Newton's Cradle I had on my dresser as a kid. A visual reference of the physical characteristics of things that occur and can be seen throughout the natural world around us. I want to build one of these machines. It would be great at parties. BRILLIANT!
I have been looking for this for 30 years. I went to the Navy Electronics Technician A School. It is the best visual demonstration of transmission lines.
surfs up Waves awesome dude. Maximum shear occurs at nodes in structural analysis. FEM today makes this much easier to calculate. Awesome film Thanks.Shalom
A guitar string has a standing wave ratio of infinity, and gears and levers are impedance transformers promoting the transmission of the energy of motion . Just two of the many things I've learnt in 26 minutes watching this lecture.
Excellent point about studying an area that deals with waves extensively allowing you to understand any other area that where waves are fundamental to the field; absolutely agreed. Particles and waves are what everything eventually comes down to.
Am I missing something, or are the electrical diagrams reversed for reflection? A short reflects inverted to match the boundary condition of a zero sum for impinging and reflected waves, no?
At a short the boundary condition is zero voltage. A +ve incident voltage wave is cancelled by a -ve reflected wave. For an open circuit the boundary condition is zero current and again the incident and inverse reflected current waves cancel.
@@MohammedAli-ig2nu Thanks man, you are so right. He actually explicitly says so between 5:00 and 6:00. I wasn't paying enough attention; the boundary condition for current at an open end is 0 current, so the reflected current is inverted indeed as Pete Singleton and you point out...
Is he saying our voices are never as loud as they could be because we humans have been suffering from power loss due to impedance mismatch from our throat to the open air, which is an unterminated transmission line? Have to try and see if my throat feels less vibration when using a megaphone.
good advice! This is ehat I did as I work on shortwave frequency that I can only mesure with my oscilloscope I decided to experiment also with light and audible frequency as they all behave in the same way but it is easier to understand them when actually we can experience them by hearing or seeing (like sound or visible light) .
I propably misunderstand the logic, but if the clamp represent an open circuit i.e. Zload=large, and the reflection coefficient is approx. (-1) because the wave is inverted. From wiki -"(complete negative reflection, when the line is short-circuited,)", and if you check the formula ((reflection coefficient=(Zload-Z)/(Zload+Z))). This formula and the wiki implies it's the other way around. Any clarification is appriciated, and thanks for a excellent video!
But a short and an open circuit are opposit of each other, then a short=-1 and an open=+1. But I see others have pointed this out allready. Thanks for the answer!
You just wonder how they were able to explain things so perfectly decades ago with tools that looks like toys today. I would say engineers and scientists were really much much better in those days than what they are today. Again I wonder why!
Bell Labs - A National Treasure allowed to go to seed. However, "The Labs" lives on through the thousands of skilled scientists and engineers that pass through it's portals.
+1 Excellent (Perhaps Tech Studies classes can use their materials workshops to make similar machines, eg, as school fundraisers? Sell the machines & accessories to other schools & libraries, eg, at a fraction of the current Sci.Lab. supply market does.) Now, where is a video of the system of components - represented by their mechanical analogs, eg, a capacitor (by a small sealed drum-like analog), etc. I seem to recall that the system represented both AC & DC current flows, as well as impedances & resonance, etc. - to be found?
His electrical example on the chalkboard is wrong. A electrical short reflects a inverted wave. An open circuit reflects a wave of the same polarity. The exact opposite of what he has on the board. See a you tube video entitled "Tektronix - Transmission Lines" for a measured example. The rest of the video is quite well done.
1 undergraduate semester of studying obscure topics such as Transmission Lines and Waveguides and smith Chart and stubs was made clear by a 30 minute-long video. This makes me happy and sad... (sad coz my undergrad professor succeeded in turning an interesting topic into a lullaby)
If any "God" exists, I would like this guy be blessed for eternity! and I'm even not "a believer"! Very Well Done (again) and thanks to the people have made possible to share his so clear and bright understanding :bd
A solar probe (or even a manned cylindrical craft) could be design Just Like This. There are other things to considering, like the electromagnetic bubble (and foam) that protects the solar system from deep space radiation, and integrating that with a transformer, Solenoids, generating Huge Magnetic Fields Without a Superconductor, taking into account all the shear forces, Heat, Turbulance, and other design characteristics to enable it to move without using traditional thrusters- this Should Be the Backbone of Future Space Travel and Design. The Wave Machine.
