HTML-код
- Опубликовано: 28 сен 2024
- An introduction to why and when terminations are needed for transmission lines in both high speed digital applications and RF applications. 50 ohm termination examples are given, but the principles apply for other line impedances as well. The basic operating principles of signal propagation down a transmission line and the effects of reflections coming from improperly terminated are covered. Examples for digital-like signals as well as RF signals are given. A description and examples of what is meant by Standing Waves is also given. As a bonus, the properties of quarter wavelength transmission lines in RF applications is also presented. Notes from the video can be found here:
www.qsl.net/w/w...
I think that video is a 100 years of RF experience packed into 19.14 minutes.
Software/electrical engineer here. When I'm trying to brush up on a topic and stumble on your videos, I always take time to watch. You have a real knack for explaining things in simple terms. Thanks for sharing the knowledge!
I'm glad you're enjoying my videos and find them useful.
Nice visualization of standing waves! Great video all around!
omg applied science!!
I am of the opinion that the world is a better place with you on it.
+RenanzinhoSP Thank you!
Agreed. We need more w2aew's running around.
RSP I agree! :-)
Totally agree with you. Best explanation among I've ever learned in universities for over 10 years
Of course!
The reflection in the piece of plastic is absolutely brilliant. I'm busy watching all your videos, incredible wealth of knowledge.
watching this video again after seeing it a year ago and it never ceases to amaze me how well you explain complicated topics. I greatly appreciate your efforts in making these great quality videos and sharing them with everyone! Thank you and please know a lot of people have benefited from your knowledge and teaching abilities!
Unbelievable. I have no words that can describe my thankfulness for what you are doing. I want to cry and hug you.
By FAR the clearest explanation I've seen about line termination, wave reflection, standing waves, etc.
Your videos are all outstanding.
Thanks for sharing your knowledge!
Great video. This helped me troubleshoot a problem. I recently purchased an HP 3589A off ebay. I bought it to learn more about network analysis. I watched your video on dBm, bBu, etc., but my results were way off. I was afraid the analyzer was out of calibration, but when I ran the test from this video, I noticed my terminator had no effect. I measured the terminator and found it open. Replacing it, I was able to observe the results you show in this video, and found my 3589A measures correctly with the proper termination. I also learned that buying cheap terminators off Amazon.com is a mistake. Thanks for the good work.
If I could, I'd give you not one, but one million likes for every single video that you've made.
now THIS is why I had to plug in those little shiny terminators when I helped to build a coaxial ethernet network back in school. now, 25 years later, I finally learned it.
I don't know if you teach for a living but you're quite skilled at it (i would say gifted but that doesn't pay proper respect to the level of effort you put into it). I've been tinkering with amateur radio for a while now and I know for a fact that i have learned and relearned what impedance matching is and how it can affect signals...but until now I've never really had more than a tenuous grasp of the concept.
Somehow just watching you walk through the propagation on paper in the first couple of minutes is what really did it for me (impedance matched lesson i suppose, lol). Seeing it all play out so clearly on the scope is such a modern luxury and just drove the point home that mind-boggling speeds and inconceivably short timescales don't somehow give you license to ignore the details...they still matter greatly.
I guess all this is just a verbose thank you, but i didn't want to cut any of it out. :)
Thanks!
My favorite channel w2aew. Thank you very much for wonderfull videos/lectures.
What a beautiful explanation! How many of us have been told that 'energy is reflected' but have never understood *how* it's reflected? What causes the electrons to travel back to the source? I've searched but have never seen an explanation--until now... Now I understand!! Excellent presentation!!
WOW, thank you for sharing your wealth of knowledge with us again, but more over your ability to transfer this wealth is amazing. Thank you.
You are a premium resource for electronics on par with the best . I have seen this a few times for both electronic review and non electronic purposes .ty
Much better explanation than my professor gave us for a lab we did a few weeks ago! By explaining the application of this technique it becomes crystal clear. Thank you!
Another great lesson! You never cease to amaze and inform me.
Thx
Excellent video and the best explanations on SWR graphically...
Enjoyed IMMENSELY. Answered a number of questions I had. Many ah-ha light bulb moments... TEACHING: The most honorable, invaluable professions next to a ER doctor saving my life 😉 Thanks so much 👍😁
I will treasure this channel. Absolute love.
I can't stop watching your vidoes. So good that I can learn something even when I'm familiar with it.
Nice one. A much better explanation than any of my tutors ever gave who solely relied on the mathematical explanation.
Transmission lines are so fundamental.
It should be more emphasized in school the way you've done it here
I am studying for my ticket, and now I know about why SWR works in coax transmission lines.
Thanks, Alan!.
Thanks! Great explanation and demonstration. My first transmitter (a little FM bug circuit) transmitted well at 89mhz.....and 92.....and 94.....and 105.... Now I get it! Thanks.
Love this video, i am a curious hvac technician and i am sure nothing is useless in knowing in how the things work.
When you have a no wanted noise in a boiler exhaust pipe, you make a T with an adjustable cap to change the lengh of the pipe without issue. And adjust the lengh at the frequency you want short circuit.
I am very bad in english, learning since 35 years 😭😭😭
Now why didn't my instructor in EE 101 lab make us perform this experiment. This is the best description of standing waves I have ever seen!
Very usefull, I have not studied this field well in my tech life and I learn every day, thanks
Excellent as allways. The old teaching; fitting impedans to impedans from end to end or output to input.
Thank you so much for your videos! Seeing a visual representation really makes things much easier to understand.
This is the best explanation I've ever seen.
Im going to tech college in the fall so all of these lessons are awsome! Thank you
Brilliant. Extremely clear and coherent explanation. Thank you again Alan for a fantastic video!!
Wow. Ask you you shall recieve. I requested a video on this subject last week and we all got a very clear, understandable and well demonstrated summation. Thanks Alan
it was an annoying question asking to myself since years , now i have the answers thanks to you
Another excellent explanation of a difficult to grasp subject. Alan's
my go-to guru.
Very good explanation, I finally understood what needs to be perfect matches between the transmitter antenna, and what should be Balun end of the transmission line! Thanks
wow again you are so great and accurate. I have termination resistors on can bus lines and i never knew why but now i do for sure. you are amazing with all you details. i really liked the math that proves the distance of your tapping point. i am such a rookie that this is mind blwing stuff right now. you have this stuff down to a science.
A fountain of well presented knowledge, first class as always.
Thanks Alan AGAIN! Perfectly well explained in simple terms, perfect! Keep them coming and thanks again!
Thanks for the very clear explanation!
You have great skills in education...i like your vids...thank you...best regards from Austria (not Australia ) ;-)....
you are amazing really
you are the best teacher in all youtube
long healthy life for you
thanks
Can't thank you enough for all of your videos. Great information, thoroughly explained.
Nice! Finally someone can teach!
This is really helpful along with your other videos, I am getting close to understanding standing waves and impedance matching. One question in relation to this video, your SG outputs a 10Mz signal with an output impedance of 50 Ohms and your load has and impedance of 50 Ohms so you you minimise / eliminate any reflections and hence maximise the power transfer to the load. However you tap into that with a 1 Mega Ohm load resistance on the scope (Ch2) and this does not cause any reflections back onto the line ?
Any help would be appreciated.
Thank you Paul M0HPP
Yes, mainly because the physical/electrical length of the Tee that leads to the 1Mohm scope input is very short with respect to the wavelength of the 10MHz signal. Thus, any effect of this impedance discontinuity is minimal and the reflection off of the scope input impedance is minimal. However, if the signal were at 500MHz instead, then the 2-3" of coaxial length leading to the scope input would be a "significantly" long stub and would definitely create a significant reflection and impedance discontinuity in the line.
Very good video. Describes the behavior very well. Thank you.
Excellent video and best explanation I have ever seen
Even though I do not value our current schools in the world at all, If you were teaching electronics at a school or university, I might actually come to the US sir!
Congratulations to you about your experience
Thanks for excellent demonstration! very helpful !
Some questions to sincerely consult. Please correct me if I was wrong.
1. at 7:27, the end signal is doubled in Amplitude and distorted in waveform details. I think the distortion is caused by impedance mismatching indeed， while I think the doubling is because your signal generator(GEN) is set as "50 ohm load" condition, which means GEN will "thinks" you will connects a 50ohm load and so it will ACTUALLY output a 2Vpp voltage if you setting value is Vpp on its input panel, and therefor you'll get a Vpp measured and dislplayed on oscilloscope under 50ohm input impedance setting. When you changed to 1Mohm oscilloscope input impedance setting(and keep GEN setting unchanged), the measured on oscilloscope would be 2Vpp, which is doubled. That is my personal thoughts.
2. If my perception above is correct, for a simple system with certain source impedance(Rs) and source voltage(Vs), say 5MHZ 1Vpp(Vs) square wave and 50ohm Rs, if I need a GOOD square WAVEFORM (nice and clean as you said in video) on receiving end , I of course should use 50ohm load termination, but this will cause the received voltage to be reduced by HALF (Rs and R_load forms a divider), so I will get only 0.5Vpp on my load resistor. Seems I have to choose between the "undistorted waveform" and "valid voltage" ? Seems no way to have them both. Any comments?
Thanks again.
Yes, you have it right. I did another video on the topic of source impedance and output voltage: ruclips.net/video/tClE8s6RZdg/видео.html
Did everyone also notice when Alan altered the frequency to show the null point in the standing wave and then went further (time 15.53 in the video), that the centre tap sine wave was 180 degrees out of phase with the end of the cable? In other words, the two scope waveforms started off in phase and as the frequency was increased, the centre tap went through a null before increasing again, but now in anti-phase.
Excellent . The best explanation I was looking for! great job
I enjoy your video very much. It answered many of the questions in my mind. Thanks for sharing your knowledge.
Very helpful and straightforward! Thanks very much! I wish I've seen this earlier!
Thank you, this is an outstanding video. I love your presentation style and explanations.
brilliant demonstrations... what if consciousness is the standing wave ring in the neuron transmission lines of our brain?
Brilliant tutorial! Can you explain a little bit why the amplitude of the output sine wave signal in your last demonstration varies as you increase the frequency? It stays pretty much the same at lower frequencies but starts to change wildly in the higher range. Why?
The amplitude varies at the output vs. frequency because the load seen by the generator varies with frequency - resulting in a different divide ratio against the generator's 50ohm output impedance.
The best explanation about transmission line!
glad i found your channel. Such a good teacher.... Thank you.
Another incredibly useful video.. thank you! I guess if you know the signal frequency and the exact cable length, it's easy to figure out the velocity factor if that's your unknown, and you could look that up to get an idea of what the dielectric is. Neat! Permittivity is tricky stuff on a physical level. But same with simple electron propagation really.. involving fermi surfaces and various quantum phenomena..
Incredibly educational video!
Very great and educational video, I'm wondering how you move the wave at about 13:18 in the video ?
A little analog scope trickery - The sum waveform is used as the trigger. I very slightly changed one of the input frequencies (by less than 1Hz), which causes it to move with respect to the sum. It's not exactly what happens on the line, but visually represents the standing wave phenomenon.
That's clever, thanks for the explanation
I was wondering the same!
An excellent explanation. Thank you.
Excellent explanation. Thank you so much.
Great explanation
Excellent Video.... Very well explained...practically.
oh man, your introduction is so nice! Thank you for providing such good vedio, it really helps me a lot!
Thank you, Alan. This means a lot
I guess in a way this also represents a bifilar coil which may be considered a transmission line with distributed inductance and capacitance. In essence we have conditions of lower and higher potential on a piece of copper...if very high potential we have Tesla's hairpin circuit and magnifying transformer. Excellent video, thank you!
amazing explanation of reflection i have ever seen
thank you so much
keep going please
So this is What Limits the usb Legnth to 5 meter without Any Active usb signal Regenerator ?
How did you move the two signals so that one looked like the incident wave and the other looked like the reflected wave?
I fed CH1 and CH2 with the two channels of my function generator, and used the scope vertical controls to also show the sum of the two channels. I set the trigger to be on the "vertical mode", so it is triggering on the sum signal. Then, I adjusted the phase of one of channels of my function generator which moved it in one direction. Since I'm triggering on the sum of the two, that made the other channel appear to move in the other direction.
Thanks Alan , you are the best
I've re-watched your videos on this topic plus a few more I've found online trying to make sense of a confusing discovery I made at work today. An Allen-Bradley remote IO link specifies a different terminating resistance at different baud rates.
57.6k and 115.2k baud spec a 150 ohm resistor while they spec an 82 ohm resistor for 230.4k baud rate. The cable they use is a Belden #9463 with a characteristic impedance of 78 ohms. I've always thought a terminating resistor should match the characteristic impedance of the cable and that the protocol wouldn't have any influence on this value. Any ideas?
Thank you as always Great video Well explained!!!!
so if you only have one load, then it doesn't matter if there is reflection. An LVCMOS33 source driving and LVCMOS33 input, 6 inches away, will get the digital signal through, even if there is reflection in the middle.
Excellent
Why does data signals that use a twisted pair wires need to have a termination resistor to prevent "echo"? Data signals aren't an RF signal so I'm not understanding why would the data "echo" if there is no termination resistor.
very good knowledge. well done job
thanks a lot again.
Excellent video as always. Thanks!
Question for you: Why is there a (lambda/4) difference between voltage and current in a mismatched circuit. Is there also a maximum and minimum power value along the transmission line?
What a great lessom this was thank you. It gives me alot to think about both on my bench and my ham shack.
Do you have any videos on feed line length and velocity factor for rf applications?
You'll want to look a these videos:
Using a scope to measure the length & impedance of coax: ruclips.net/video/Il_eju4D_TM/видео.html
Using a scope to measure velocity factor: ruclips.net/video/TpIIftvQPFM/видео.html
Visualize standing waves: ruclips.net/video/M1PgCOTDjvI/видео.html
Can you make a fiber optics video representing the same issue?
hi
thanks for this video and i hope if you can show me how build an 50 ohm termination for oscilloscope
Great vid. Great visualisation. .
Thanks. How coax cable impedance change vs frequency, for which frequency range it is actually 50 or 75 Ohm?
Superb explanation. Thanks!
Hi, thank you for your great videos, I did find them very educational and easy to understand in the deep level. Recently I was wandering what is the difference between RF and AF? I mean I understand that RF is electromagnetic radiation and AF compression waves but audible frequency goes as hi as ~20khz and RF can go as low as 3khz. So if I switch my signal generator and start cranking frequency up where starts rf and where af ends? 🙂 Any chance you could do the "Back to basics" video on this topic? I tried to google about this, I asked this question in many ham radio facebook groups but no one could explain this clearly.
Kudos. Excellent explanation as always. A quick question:
Does plugging both the end and the middle into the scope have an effect since the two channels are internally grounded together? This essentially shorts half the return path of the transmission line - does this matter??
It does not matter - you will have the return/image current flowing in the shield of the coax between the scope inputs.
Outstanding! Thank you for that.
Great video, very informative, however if I understand it correctly, when we match the source line and load, there won't be reflections but the voltage at the load will be half of the source? If I need the voltage at the load to be the same as the source it sounds like I can either match everything and have a driver that is twice the voltage my load will need or I can change my load impedance to have a reflected in phase wave to bump up the voltage at the load to the source voltage?
Yes, both of those are correct.
Did you say "Why we need Terminators"?
very well explained very clear!
termination resistors in digital circuits that use twist pair wires.The termination resistors prevent noise immunity? and the digital signals edges are sharped edges. If the termination resistors aren't there the digital signals edges are messed up from the reflections?
termination resistors are to prevent distortion due to reflections.
The FM/AM modulation meter is long due for re-calibration!!!
Do different inductances actually create harmonics on a line?
no, not to my knowledge.
Alan, hope all is well. Is a T - connector plugged with a 50 ohm end lug "stub" connector as good as a 50 ohm feedthrough terminator when used on an oscilloscope that doesn't have internal 50 ohm impedance? Your thoughts, and is it worth a video showing what happens?
This will work for frequencies below 100MHz or so.
Newcomer to your videos - excellent stuff, clearly presented - keep 'em coming! (& please add me to your ever-growing list of 'I wish you had been my science teacher' :)