I have worked in the radio and radar industry for over 52 years and never fully understood the operation of transmission lines. This movie taught me more in 23 minutes about transmission lines than i learned in those 52 years. Kind of makes me wonder how many antenna jobs i screwed up!!!!!
Ted Swimerr I agree.. I understand the math but never really understood the real physics.. Imagine how much more we could fully understand electronics if all concepts were explained so well....
@@bradleysmith681 They are explained just as well and better if talking to the right people. I have known this for more than 30 years. Want to see one even worse try chasing down a ground loop sometime...
When MIT tried this sort of thing in the 1990s, the students rose up in arms, and got rid of it. (This was Belcher's E&M course, with animated field-diagrams.) They wanted obscure math only. If it's taught without math, with visual-intuitive animations, then any mere technician can understand all the concepts! They put a stop to it. (The student-revolt was among physics students. It's like having a bunch of Medieval pre-meds who eliminate any professor who would teach, not in proper Latin, but in English which any outsider could understand.)
After watching this kind of videos you're left with a profound sensation of awe and satisfaction about the vibe and delivery of this kind of content, now old style videos. Glad some of them are preserved in time in here...
I was watching this at 2× speed, kind of bored until about the six minute mark... and then I sat up and said, _whoa!_ I had to rewind because I'd never learned what characteristic impedance actually was. I knew the effect of an impedance mismatch was that the signal bounced, but I didn't get _why_ it did. In rapid succession there were three key things this video taught me about high frequency signals: 1. The insulator between conductors, even if it is air, is the "dielectric" of a capacitor. 2. Every wire, even an ideal one with zero resistance, has inductance. 3. To make it easier to conceptualize, it's okay to chop up the line into multiple segments of repeating inductors and capacitors that pass the signal one to the next. Also helpful was the reminder that the characteristic impedance Z = sqrt(L/C). Increasing the length of the cable increases L at the same rate it increases C, so it cancels out when calculating Z. Therefore, 4. Theoretically, a cable will have the same characteristic impedance no matter how long it is.
Some people might think that this video is boring but actually it is exciting if you use imagination to understand the principals. Consider that these are also the principals of acoustics where a "reflection" is called an echo. A string on an musical instrument behaves exactly the same way constituting an acoustic transmission line with a small load, the string is plucked or bowed to create a pulse, this pulse travels to the end of the string and is inverted and reflected, then it is reflected again and re inverted off the opposite end. The pulse moves back and fourth making a tone that gradually decays. The instrument body functions as the load and the players motions as the temporarily connected battery. The pulse contains many harmonic frequencies and the nature of the load(the instrument body) verses the length and structure of the string determines the standing wave properties that filter the harmonics which provides the timbre (the tonal quality) of the instrument. Your breath is a battery, your vocal chords are a switch, your throat and nasal passage are two acoustic transmission lines and the air outside your lips and nose are the load. The transmission lines in this case are very complex with different adjustable impedance's distributed along their length( unlike an electronic transmission line with its consistent impedance) such that the end result is you can sing and speak. Most people think electronics are very abstract and remote form day to day existence but you are using these principals every to time you speak, you are appreciating these principals every time you listen to music.
This video not only opened my eyes, it also open my skull, erased what i thought i knew about transmission lines and put back what i should know about transmission lines. Thanks for sharing it.
In 1961 Tek introduced the 519, capable of viewing 1 gigahertz on a tiny portion of the CRT screen. In 1980 they had a mass produced 1 gigahertz scope, the 7104 with full screen width and height deflection, and high brightness viewing due a micro channel plate CRT that acts as a electron beam image intensifier. It is an amazing bit of kit. I own 2 of them.
Good stuff. For those who didn't know, the PC pci bus works like that reflected flattop signal at around 20: min. The driver only makes half the amplitude/current to get to logic level and the bus is sampled at reflection time so things see the full desired level. Fairly slick, but obviously length dependent in the extreme. If anyone worked with ECL back in the day, the only other good reference for this work was from Motorola ECL design handbook...and I still use the knowledge today.
I actually screamed out loud at 13:38 because it offended my senses of what should and should not happen so deeply. I knew why and understood but never was it displayed so clearly to me.
Wow! I stepped in a time machine here! That is some old footage. Best explanation I have heard on what is characteristic impedance. Very good info here!
We used tectonic oscilloscopes, when I was employed by Western Electric AT&T. It was to me, like a mechanic is to a wrench, or to a hammer is to a carpenter. In my opinion they made the best oscilloscopes available at that time.
Thanks for posting this!! Best explanation ever! Now I understand the basics that I've been looking for. These old training videos destroy anything produced today. If anyone wants to see some great explanation of antenna theory, look up the old videos titled "Antenna Fundamentals"
Now I finally understand transmission lines, characteristic impedance, and reflections. Now to apply this knowledge in the real world to RF and in helping better understand antenna theory. Though I still wonder why impedance matching and reflections aren't an issue at low frequency, with electrically short conductors (transmission lines). Particularly in the Audio world where power amp output impedance is ideally 0 Ohms, going into a load of a few to a few hundred Ohms. Oh, is it that the characteristic impedance of a transmission line is high enough to be negligible at low frequencies?
University programs are mostly overpriced trash. More often then not someone has to get over a language barrier before they can start to understand and integrate the basics. I love these videos.
Ronnie was a smart guy and knew quite a lot about quite a few things. He may well have known how a transmission line worked. However, I highly doubt he went up to Beaverton to voice this video. :-)
For a short circuit, the return signal was said to be reflected. But aren't the short circuit's 2 emitted pulses each just transmitting through the short circuit to cross to and return in the opposite line, which explains the short circuit return signal's opposite polarity?
Well yes, but the major point is that the signal doesn't disappear at the end, it returns. And by convention we call that return a reflection when talking about transmission lines, regardless of the exact mismatch phenomenon causing the return. (If we were talking about radar, the reflection of the energy from the target is called a "return", just to be confusing.)
@@lwilton Thanks. I think that, because there really is no reflection in a short circuit, to avoid further confusion, the convention should be changed. I don't find the radar reflection to be confusing, since it really is a reflection.
![I.N "HALLUCINATION" | [Stray Kids : SKZ-PLAYER]](http://i.ytimg.com/vi/n5B5q1Hwt_U/mqdefault.jpg)
I've been working in radio and electronics for almost 30 years, and this is the best explanation of transmission lines that I have ever seen.
Absolutely!!
Even better when you can have hands on in a lab and see the stuff first hand.
Me too! Lots of things so easily clarified.
I have worked in the radio and radar industry for over 52 years and never fully understood the operation of transmission lines. This movie taught me more in 23 minutes about transmission lines than i learned in those 52 years. Kind of makes me wonder how many antenna jobs i screwed up!!!!!
Ted Swimerr I agree.. I understand the math but never really understood the real physics.. Imagine how much more we could fully understand electronics if all concepts were explained so well....
@@bradleysmith681 They are explained just as well and better if talking to the right people. I have known this for more than 30 years. Want to see one even worse try chasing down a ground loop sometime...
When MIT tried this sort of thing in the 1990s, the students rose up in arms, and got rid of it. (This was Belcher's E&M course, with animated field-diagrams.) They wanted obscure math only. If it's taught without math, with visual-intuitive animations, then any mere technician can understand all the concepts! They put a stop to it. (The student-revolt was among physics students. It's like having a bunch of Medieval pre-meds who eliminate any professor who would teach, not in proper Latin, but in English which any outsider could understand.)
After watching this kind of videos you're left with a profound sensation of awe and satisfaction about the vibe and delivery of this kind of content, now old style videos. Glad some of them are preserved in time in here...
I was watching this at 2× speed, kind of bored until about the six minute mark... and then I sat up and said, _whoa!_ I had to rewind because I'd never learned what characteristic impedance actually was. I knew the effect of an impedance mismatch was that the signal bounced, but I didn't get _why_ it did.
In rapid succession there were three key things this video taught me about high frequency signals:
1. The insulator between conductors, even if it is air, is the "dielectric" of a capacitor.
2. Every wire, even an ideal one with zero resistance, has inductance.
3. To make it easier to conceptualize, it's okay to chop up the line into multiple segments of repeating inductors and capacitors that pass the signal one to the next.
Also helpful was the reminder that the characteristic impedance Z = sqrt(L/C). Increasing the length of the cable increases L at the same rate it increases C, so it cancels out when calculating Z. Therefore,
4. Theoretically, a cable will have the same characteristic impedance no matter how long it is.
Some people might think that this video is boring but actually it is exciting if you use imagination to understand the principals. Consider that these are also the principals of acoustics where a "reflection" is called an echo. A string on an musical instrument behaves exactly the same way constituting an acoustic transmission line with a small load, the string is plucked or bowed to create a pulse, this pulse travels to the end of the string and is inverted and reflected, then it is reflected again and re inverted off the opposite end. The pulse moves back and fourth making a tone that gradually decays. The instrument body functions as the load and the players motions as the temporarily connected battery. The pulse contains many harmonic frequencies and the nature of the load(the instrument body) verses the length and structure of the string determines the standing wave properties that filter the harmonics which provides the timbre (the tonal quality) of the instrument.
Your breath is a battery, your vocal chords are a switch, your throat and nasal passage are two acoustic transmission lines and the air outside your lips and nose are the load. The transmission lines in this case are very complex with different adjustable impedance's distributed along their length( unlike an electronic transmission line with its consistent impedance) such that the end result is you can sing and speak. Most people think electronics are very abstract and remote form day to day existence but you are using these principals every to time you speak, you are appreciating these principals every time you listen to music.
wow
amazingly written
This is the first time I have understood impedance, reflection and velocity factor. Thank you for sharing this.
Best education on transmission line theory on the planet. This video can teach you more in minutes than months of hap-hazard classes in EE college
This video not only opened my eyes, it also open my skull, erased what i thought i knew about transmission lines and put back what i should know about transmission lines. Thanks for sharing it.
best depiction of basic transmission line theory in spite of age. Thumbs up.
Tektronix had a CRT scope in 1950s capable of a bandwidth of a few hundred MHz, very impressive
In 1961 Tek introduced the 519, capable of viewing 1 gigahertz on a tiny portion of the CRT screen. In 1980 they had a mass produced 1 gigahertz scope, the 7104 with full screen width and height deflection, and high brightness viewing due a micro channel plate CRT that acts as a electron
beam image intensifier. It is an amazing bit of kit. I own 2 of them.
Good stuff. For those who didn't know, the PC pci bus works like that reflected flattop signal at around 20: min.
The driver only makes half the amplitude/current to get to logic level and the bus is sampled at reflection time so things see the full desired level. Fairly slick, but obviously length dependent in the extreme. If anyone worked with ECL back in the day, the only other good reference for this work was from Motorola ECL design handbook...and I still use the knowledge today.
Oh my gosh, that's absolutely amazing, I'd like to find more Information on this. Any other links or book titles?
I feel old videos somehow hearth-warming :D
100%. What people designed/made/did back then, doing their calculations on paper and slide rules! Really amazing. They had to know their stuff.
I actually screamed out loud at 13:38 because it offended my senses of what should and should not happen so deeply. I knew why and understood but never was it displayed so clearly to me.
If i binge watched these videos 20 years ago in college, things would have been different 😅❤❤❤ magnificent..
Thanks a lot for this video I wish there are more of these kinds of videos explaining fundamental things in telecommunication Engineering :)
Wow! I stepped in a time machine here! That is some old footage. Best explanation I have heard on what is characteristic impedance. Very good info here!
Certainly this explanation of reflected waves from transmission lines is the best I have seen.
Vintage, timeless, awesome!
We used tectonic oscilloscopes, when I was employed by Western Electric AT&T. It was to me, like a mechanic is to a wrench, or to a hammer is to a carpenter. In my opinion they made the best oscilloscopes available at that time.
Yup, we still use Tektronix in research labs :D
Thanks for posting this!! Best explanation ever! Now I understand the basics that I've been looking for. These old training videos destroy anything produced today. If anyone wants to see some great explanation of antenna theory, look up the old videos titled "Antenna Fundamentals"
Wow - how good was that eh? Brilliant. So well explained. Thank you for uploading it and making it available for us to learn from.
This is such a well made lecture !
Best explanation of transmission lines I ever saw. Simple, clear, concise, complete, tranquil, structured. Leads by example.
Great video, and great job explaining this concept from the ground up.
These old videos explain principles and examples so much better than modern videos! 👍🍻
this is the best video I have ever seen about impedance matching, thank you !
Now THIS... is a transmission line
Thanks for the video! That's what i've been looking for.
great video.
seeing is believing.
This is so amazing yet simple at the same time. I was wondering wtf that 50 Ohms thing was, the video makes it so intuitive>
Amazing! i watched this with plesure
If you're still having trouble, AT&T Archive has an even better video; Similarities of Wave Behavior by Dr. John Shive. Definitely worth a look.
Fantastic!
it have been explained well....now i had go idea about transmission line...thanks
thanks for sharing
nothing less than pure gold
Well presented and fun explanation - good job.
Thank you very much for sharing this gem.
Better than tutor I met before. Thanks for the video.
Great video !
Thanks for sharing this video.
Bless your mind for uploading thid! Lots of love!
Cool video. I think we had an o scope like that in school in the 70's.
The city, seen briefly at 22:25, Portland Oregon, Broadway street, as it was in the 1950s.
*Beautiful.*
very good explanation...
And here I thought I got recommended a sick techno track. Bamboozled again!
That’s really funny
A fantastic lesson, a masterpiece of explanation.
Ohhhhhhhhhhhhhhhhhhhhh.... so that's what termination is. This video makes things so much clearer.
Lernen unter optimalen, ist gleich beruhigenden Bedingungen. Sprecher, Musik, Geschwindigkei, perfekt.
This should be required viewing for any radio amateur seeking a license beyond technician-class.
Great video ! TNX 4 the upload !
That was an awesome video!
Wow...the vid was amazing.
At 14:18 can someone tell me why those two waves on scope screen do not combine?
The two waves do not combine because each occurred at a different time. The horizontal axis of oscilloscope is a range of time, not a single moment.
Magnificent
Old, but gold
Wish I had this video when I was in engineering school "a million" years ago.
it is stupid that this video is more clear up to me than google search on 2023 and my elec engineering course.
Timeless
Now I finally understand transmission lines, characteristic impedance, and reflections. Now to apply this knowledge in the real world to RF and in helping better understand antenna theory. Though I still wonder why impedance matching and reflections aren't an issue at low frequency, with electrically short conductors (transmission lines). Particularly in the Audio world where power amp output impedance is ideally 0 Ohms, going into a load of a few to a few hundred Ohms. Oh, is it that the characteristic impedance of a transmission line is high enough to be negligible at low frequencies?
Ok. With a title like that I thought it was gonna be an electro-industrial track.
where can i find this kind of old videos bout electronics and communication? please help!
On VHS in ancient school library archives.
Looks a good deal older than VHS. 16mm film, maybe...
There are some youtubbers like eevblog by Dave Jones and W2AEW about spectrum analyzers, mixers, rf signals, etc
Is this a transmission line? Is that a transmission line? Am I a transmission line? Are you a transmission line?
They don't teach like this anymore
University programs are mostly overpriced trash. More often then not someone has to get over a language barrier before they can start to understand and integrate the basics.
I love these videos.
The current (electrons) are not moving lightning fast, the field (volt) is
that was my first experiment with an oscilloscope 6 years ago
Do we know who the narrator was?
All wires are transmission lines.
Jamie well done! fantastic find. Do you know if there are any more old videos like this anywhere?
I'd have never guessed that Ronald Reagan knew so much about transmission line theory. Must have been between Hollywood gigs. ;)
Ronnie was a smart guy and knew quite a lot about quite a few things. He may well have known how a transmission line worked. However, I highly doubt he went up to Beaverton to voice this video. :-)
wait...its all transmission line?!
More Tek Awesomenessness!!! Why would you buy any other CRO if you had the money!
Point 95!
+3 dB
For a short circuit, the return signal was said to be reflected. But aren't the short circuit's 2 emitted pulses each just transmitting through the short circuit to cross to and return in the opposite line, which explains the short circuit return signal's opposite polarity?
Well yes, but the major point is that the signal doesn't disappear at the end, it returns. And by convention we call that return a reflection when talking about transmission lines, regardless of the exact mismatch phenomenon causing the return. (If we were talking about radar, the reflection of the energy from the target is called a "return", just to be confusing.)
@@lwilton Thanks. I think that, because there really is no reflection in a short circuit, to avoid further confusion, the convention should be changed. I don't find the radar reflection to be confusing, since it really is a reflection.
The Morgan Freeman of the 1950s
Guy sounds a bit like Spock.
watch?v=DovunOxlY1k This one's better, but doesn't have the same feel.