After 26 years of Navy Electronics, working at NASA, building spacecraft comm systems, this is the first time I completely understand I & Q signals. No one ever showed me on an Oscope. I finally get it! Thanks.
It's fascinating how these orgs that do such high level stuff manage to get people working functionally with stuff with only a basic working knowledge of the tech and physics involved. I always like to think of it in terms of something I think I first heard in software engineering: the black box model. They show you what need to input to a system, and what outputs you get for given inputs, but don't bother to show you whats actually going on inside the box, just expect you to take for granted that it'll work assuming you do the inputs right and know what to do with what you get out. Unfortunately, for tons of technically minded people... WE WANT TO KNOW WHAT'S IN THE BLOODY BOX. I want to know every square nanometer of everythig that is in the box, how it works, why it works, and what to do if it stops working (which, all too often, it does). Nothig more infuriating than having some system cease functioning, only for some authority figure to say "oh, well its busted, we'll send for a replacement and someone else'll fix it". Even if I cannot conceivably fix it, even if I don't have the parts, or tools, I don't like not knowing why something doesn't work as expected. Curses on the black boxes, show me whats in the bloody box!
I am a old time EE that has worked in many different fields of aspects of electronics: precision DC measurements , photo-controls, space exploration rocket components, RF , missile circuits, fiber optics. Did I understand the fine points of each discipline? NO I didn't . Sure I studied to a degree, but producing result$ wa$ the objective. I,Q techniques but the MEANS of producing a 90 deg phase a shift : I assumed it was simple BUT DIDN'T know how it was done !..until now 50 years (about 18,250 days later) .
Ditto Ditto Ditto Sir, me too!! we used the instruments, the monitor, the scope, IS that Good? Yep, Pass! instructors didn't know the theory, ...and I HAVE to see the picture in order to understand the little.
Totally agree. I was going deep into the SDR rabbit hole when this came out and it was so helpful then. Just watched it again and it's still the best I've seen since.
You know, i study electronical engineering in the 7th Semester - Specialized in RF-Design. I had 6 Subjects with 4 different profs on system theory and software receiver design. Until i watched your video i did not really understood what this IQ modulation/demodulation is all about. But you just broke down 2 years of studying in just ~20 min. This video is absolute gold. Now i have an understanding of IQ modulation. Thank you sir!
Wow. I just finished reading the ARRL handbook on IQ modulation and walked away scratching my head. 20 minutes after playing start on this video cleared up all of my confusion. Very clear explanation and very well demonstrated. The examples are golden!
Here is someone who really knows what he is talking about. So clear, so easy! This always seemed to me like a complicated matter. Not anymore! Thanks a million.
I had more "ah-ha!" moments during the 20 mins of this video than I have during my entire 10 years in telco! Thank you so much for your sharing of knowledge. This is a great, "back to basics" instruction for anyone working with any type of RF signal. Thanks again, you got a subscribe from me!
I know this is an old video but thank you for covering the foundational concepts of what I/Q data represents and showing exactly where the rubber meets the road. This information makes the more "sophisticated" topics more attainable. Thank you!
I bumped on this channel as I have to take over a RF testbench for infrared detectors during my PhD and this channel is completely what I need! Thanks! 🎉
FINALLY - THANK YOU! After years of working with Digital Video Signals for Satellites (DVB-S), I understood BPSK (flipping the carrier) modulation & vaguely understanding QPSK with the constellation diagram. Then came (DVB-S2) with 8PSK for HD & all I could manage was being able to regurgitate the BS I had been told. NOW, I finally get the nuts & bolts of how QPSK works, is assembled & deciphered, along with having a thorough understanding of QAM signals. From here I can extrapolate that for 8PSK & 16QAM. THANK YOU!
Thanks a lot - I just had the most valuable 20 Minutes of TH-cam-time since many years! They way you explain the concept us IQ modulation is perfect in its combination of simplicity and detail. I recently started to work on digital designs for rf applications (mainly BT and WIFI) and this was the first time I fully understood that concept.
It is the most satisfying tutorial so far in my life, after working in Radio Resource Management for one of the leading telco for quite a long time for the first time I was able to visualize the IQ concept. Great work and your efforts are visible. You are simply awesome.
WELL DONE Alan ! You have once again taken a deep topic and presented it a form that is easily understandable. It conveys to the viewer a working overview of the theory that powers software defined radios. Thanks again
Your didactical skills, brought light to a rather complex topic! Thank you very much for your great explanations and authentic demonstrations on your scope!
I've been exploring RF for a few months now and have watched countless videos on the topic. Your explanation of quadrature signals is easily the most complete yet simple to understand. My understanding of I & Q has just made a big leap
People need the concept illustration like this to have a solid foundation before they begin learning all the tedious and boring formulas derivation like those taught in schools . Great work for spelling it out to the world.
amazing ....for the first time in my little life i have understood what actually i was reading all my life.... thank you very much for this beautiful demonstration
5 min into the video and I already know I'm going to learn more here than an entire semester worth of college education. Plus looking at the comments of people with decades of experience saying this video helped them is a really re-assuring. I'm glad I found this while I'm still in college. I'm looking to build a career in this field and this will definitely be a stepping stone in the right direction. Thank you so much!
Excellent job on this. I've read several papers on this and finally absorbed it after about the 3rd one. Your practical approach using a scope to show the modulated signals in the time domain was a great way to tie it all together. Thanks for taking the time to put this together. No doubt that many will benefit from it. Thanks!
One of the best explanation ever, even for me that I am not native speakers, I am from Brazil. You have the ability to explain things in a simple way and make everything clear. Congratulations !
Thank you so much for this video. I can finally start to understand all the math that I have been doing blindly! You are a great teacher! Please never stop making amazing videos like this one.
excellent practical info. never seen something like this. clear diction , clear video , subject content has been delivered linearly . Great Job sir. Now I have to watch all your videos
Thank you Alan. This is a subject on which I was completely ignorant of aside of Grey code and in under 20 minutes I now have a basic understanding and a light bulb moment into understanding of a small telemetry modem I have. The thing I like most about your channel is even within a fraction of all that is electronics related, you manage to create clear and concise educational videos every week. Such a pity the "biggest" electronics related channel has lately degenerated into a lifestyle show. In my opinion content older than say 2 years should not generate income for the "professional" content producers to prevent them from resting on their laurels. Your channel is all about discovery and questions of income never arise. Channels like yours are the reason why I now rarely watch TV.
Alan. Extremely helpful video. Your description and graphics make understanding the subject much easier. Then when you put them on the scope, well that put it over the top. Seeing the signals on the scope tied all the elements together. Very much appreciate your educational videos. N2GMA
I was just started to studying RF, and i watched so many videos but couldnt uderstand the IQ stuff , thanks to you i can move further, thank you so much sir, u really explained it very clearly.thanks again.
This is, without any doubt, hands down, the best explanation of quadrature signals that has ever been created anywhere, in any format, including world-class textbooks. You deserve respect.
Wow, excellent tutorial. I never really understood phase shift keying, but you made it perfectly clear. I feel like I've progressed from the 20th century to the21st!
I took the RF series at university and I learned so much more practical information from you in such a short period. It definitely helps at work and my ham knowledge.
Best I/Q mod/demod explanation I've came across in university and workplaces, so glad I stumbled upon this video in desperation of trying to understand I/Q. sub'ed.
Absolutely the best description of this seemingly complex subject. I worked as a video engineer for many years, and looked at these i/q signals on the scope without fully understanding them. My only wish is that you did a little more explanation of the demodulator side of the i/q signals in a receiver. I kind of get it, but would love, 10 years later, if you could help me with it!
Excellent explanation, I guess there is no point of college any longer for a self learner, just good text-books with TH-cam tutors like w2aew are more than enough to gain that precious knowledge.
Fantastic video. I've searched through a few IQ explanations on youtube, but the manner in which you've laid this out makes it the first one to make it 'click' for me. The use of the oscope is inspired - it allows you to see the 'real time' changes, as opposed to videos that use demonstrations in pure software, which are often far less easy to grasp. I think I grasp IQ signals much, much better now. Thank you.
W2AEW is always awesome. BTW, I was just watching this: Defcon 21 - All Your RFz Are Belong to Me - Hacking the Wireless World with Software Defined Radio . A long presentation, but some really good info and things I want to try out myself (measuring baudrate using gnuradio etc). If you haven't seen it already, you should! --... ...--
There was an excellent free Coursera on-line course given by the DSP group at EPFL (Switzerland). I think they run it every year. Well worth doing to get a solid mathematical foundation on the topic. www.coursera.org/course/dsp
Such an incredible well put together lesson. I'm just getting into EE and RF and these are the things I wish I asked my grandfather to teach me before he became unwell. He had a great mind for RF. Thank you sir!
Samy Kamkar lol, just watched one of your old conference in which you talk about signal modulations. Wanted to understand more about it and here I find you xD
As a CATV engineer I have to say this is one of the best short training videos that I've ever seen accurately describe QPSK/QAM. Thanks for putting this together! Do you have anything you can share concerning OFDM?
I've become curious about SDR lately; you haven't thought about presenting a small SDR DIY project or something like that? One question: for demodulating IQ, how do you know what phase is, well, zero? The phase-varying signal doesn't tell you by itself. For digital signals you could just let the transitions, rather than the levels, represent bits, but for analog signals wouldn't you need to know the "in-phase" time?
You generally don't need to know where "zero" is. You're really only interested in the changes. So your arbitrarily normalize at any point, and track variations from there. Amplitude as SQRT of sum of I squared and Q squared, phase as arctan(Q/I), and frequency as d(phase)/dt.
Love modulation demodulation videos. I did my Senior Project on Blind Signal Modulation Classification using Cyclo-Stationary and Cumulants analysis. I found I have a skill there, which now i am letting it die off as an IT. Seriously, engineering is the best place in the universe. It is a place for me because there is where i withdraw myself. Love seeing mixers churning signals out.
I love this video with you clear and concise explanation and followed with a real life signal analysis on a test instruments. This makes your tutorial video worth a lot more than gold! As famous saying goes, "A picture is worth a lot more than words!" The signal theory, followed by how they interact with each other, the simple math and visual explanation of Phasor diagram. Concluding with explanation of the signal analysis on the scope, helps to expand the difficult subject in a clever and concise way for the novice. You did a very wonderful job and I love it! I have tried writing a procedure on this subject, for testing mixers. You did a great job with your explanation and video. Thank you!
w2aew do you take place in university? Your videos are very fluent and easy to understand, academical. You explain things in very clear and understandable way. Thumbs up!!
So this is really fascinating, and I have a question. How in the world can you pull I & Q out of a waveform? How do you know what the phase offset is? How can you know if the phase is being modulated from 0 at all? You have a single waveform, how can you possibly know that it is the product of two waveforms. Example: I have a number, 45. Get the I & Q from that. Can you do it? Did I add 20 and 25? Did I add 1 & 44? did I add 0 & 45 or 45 & 0? You can't know! how can you pull I & Q out of a waveform unless you already know what I or Q are?
naikrovek The answer is - you don't *pull* I and Q out of a waveform. You *generate* I and Q by mixing the incoming signal with a pair of quadrature local oscillators. Phase becomes relative. Pick an arbitrary starting point, then observe how phase changes with respect to that point. Any difference in frequency between the incoming signal and the local quadrature oscillators will show up as phase rotation vs. time.
Just as I stated in the previous reply. There is no absolute phase reference point. So, you compute the phase via arctan(Q/I), pick a desired reference point and then measure phase changes relative to that user selected starting point.
Fantastic video!!!! I really appreciate the work you put into building the physical mixers and demonstrating the modulation with your equipment there. I'm striving to understand how to modulate / demodulate signals, and this video just connected a LOT of dots. Thank you!
Hi ***** another awesome demystification for me, very easy to follow your explanation, definitely something interesting to play with. Thank you for posting. Gerry
THANK YOU!!! Really clear and finally understood wtf we were studying in uni during my bachelor's in RF. It's only now that it clicked that just like AM/FM/ASK and all the other modulation techniques what is the significant part of the carrier that we were changing.
Well done, "professor!" Was that an eevblog bumper sticker I spied? Wow, and afrotech is here too. We need a convention with Alan, Dave, Afro, and Mike. Now how cool would that be?
Add Gregory Charvat and Michael Ossmann to the reunion, too. The last episode of The Amp Hour (#214) was a mix of a lecture and brainstorm session; really good. Alan, excellent video! As usual. Regards, CH!
***** Sure! and Jeri Ellsworth too! Can you image all of you together? haha! BTW, I am waiting for my Softrock Ensemble II receiver kit to arrive, and, ahh, I have just watched your video on the HotWheels radar analysis and my head is about to explode. Too muy IQ today!
Charlie Pechiar Agreed! I met Jeri once, by chance, at an airport. We were on the same flight. This was long before Technical Illusions and even before her time at Valve.
Wow, I just stumbled on the best TH-cam video I have ever seen for explaining a subject. I was looking for an explanation on QAM after watching a video about NTSC color data transmission, and how it is backwards compatible with black white televisions. The color data is hidden in the black and white compatible luminance stream, and extracted with QAM. Your explanation made it completely clear on a higher level, now it makes sense to me. I recalled doing the math in my signal theory class in college, but it never really made sense to me. Further, the basis of software defined radios makes so much more sense too. Thank you very much for this video.
Simple language , professionally explained in both sections theoretical as well as practical part…not a single word can be omitted…..superb.. Thank you sir
Why no one shows how to demodulate FM signals. I watched 10 videos and no one shows it, they just say its "easy". Well if its easy then they should show it.
Darko Bulatovic exactly. im in the same boat. it isnt clearly explained at all. it almost seems like 98% of the video is about how to modulate them, but only a brief description was given with demodulating them.
pepe6666 Given that the instantaneous phase is the arctan(Q/I), and that frequency deviation (dF) is simply the "rate of change of phase", then FM demodulation from IQ is traditionally done by taking the time-domain derivative of the phase. f(t) = d(arctan(Q/I))/dt. More details can be found here: www.embedded.com/design/configurable-systems/4212086/DSP-Tricks--Frequency-demodulation-algorithms-
+w2aew Darko Bulatovic Here is a circuit/blog I found that demodulates BPSK - I hope to give it a try. www.analogzoo.com/2014/12/amplitude-demodulating-bpsk31/ is this a proper method? (edit: trying to ref w2aew)
Raymond Tant There are many ways to do this, and this is certain one valid approach - fairly simple because it only relies on simple amplitude detection. This works OK on this waveform because the phase shift is well filtered, providing a well defined and easily detected dip in the amplitude as the phase is shifted. If the baseband signal was not low pass filtered so well, the amplitude dip would be a lot narrower and more difficult to detect this way.
Your videos on IQ are great, I learned a few tricks and a new way of thinking about a few things that really cleared up a mess in my brain......I really learned more in a few videos than a year in school. Or at least you cleared up what i had had been missing. Thank you. All your videos are amazing. You make TH-cam a goldmine of valuable information.
Good one !!! This and your video on the diode ring mixer have turned black magic into "Well that's simple!" And don't be afraid to give us the math, that's what explains it all.
Thank you again. I was looking for an IQ explanation and when I found a video made by you, all my fears were vanished. I knew by the end of this video I would understand IQ signals, and that happened. All the best for you!
Excellent explanation. Awesome. Well paced, clear, develops concepts and progresses logically, great scope shots, great diagrams. I learnt quite a bit. Thanks.
00:02 Basics of IQ Signals and IQ modulation & demodulation 02:16 Basics of IQ Signals and modulation 04:28 Varying I and Q components can lead to amplitude, frequency, and phase modulation 06:45 IQ modulation enables complex modulations through amplitude variation 09:08 Understanding IQ components in phasor diagram 11:28 Varying I or Q components between plus and minus 1 inverts the waveform. 13:50 Understanding the phase shifts in IQ signals and constellation points 16:17 IQ signals can represent any modulation type with appropriate generation of I and Q waveforms. 18:31 Understanding IQ signals and their role in modulation and demodulation. Crafted by Merlin AI.
This is the best tutorial on basic concept of Phase modulation and explanation about IQ samples. I would love to see similar content describing FFT, IFFT, IDFT concepts as well. Thanks for sharing knowledge.
After 26 years of Navy Electronics, working at NASA, building spacecraft comm systems, this is the first time I completely understand I & Q signals. No one ever showed me on an Oscope. I finally get it! Thanks.
I was also in the Navy and agree with you. There are so many areas that I do wish the Navy would go into more depth.
It's fascinating how these orgs that do such high level stuff manage to get people working functionally with stuff with only a basic working knowledge of the tech and physics involved. I always like to think of it in terms of something I think I first heard in software engineering:
the black box model. They show you what need to input to a system, and what outputs you get for given inputs, but don't bother to show you whats actually going on inside the box, just expect you to take for granted that it'll work assuming you do the inputs right and know what to do with what you get out.
Unfortunately, for tons of technically minded people... WE WANT TO KNOW WHAT'S IN THE BLOODY BOX. I want to know every square nanometer of everythig that is in the box, how it works, why it works, and what to do if it stops working (which, all too often, it does). Nothig more infuriating than having some system cease functioning, only for some authority figure to say "oh, well its busted, we'll send for a replacement and someone else'll fix it". Even if I cannot conceivably fix it, even if I don't have the parts, or tools, I don't like not knowing why something doesn't work as expected. Curses on the black boxes, show me whats in the bloody box!
I am a old time EE that has worked in many different fields of aspects of electronics: precision DC measurements , photo-controls, space exploration rocket components, RF , missile circuits, fiber optics. Did I understand the fine points of each discipline? NO I didn't . Sure I studied to a degree, but producing result$ wa$ the objective. I,Q techniques but the MEANS of producing a 90 deg phase a shift : I assumed it was simple BUT DIDN'T know how it was done !..until now 50 years (about 18,250 days later) .
Well done on this video 👍🏻
Ditto Ditto Ditto Sir, me too!! we used the instruments, the monitor, the scope, IS that Good? Yep, Pass! instructors didn't know the theory, ...and I HAVE to see the picture in order to understand the little.
As a retired teacher, I am qualified to give you an "A" for this presentation. Well done!
10 years down and it's 'THE BEST' video for the topic.
making learning a streamline.
Totally agree. I was going deep into the SDR rabbit hole when this came out and it was so helpful then. Just watched it again and it's still the best I've seen since.
The clearest explanation of IQ signaling on the web
I 2nd and 3rd that!
I couldn't agree more David, I have been pounding my brain over this, just want to yell YEAH but what IS IT? This is the best I have seen
You know, i study electronical engineering in the 7th Semester - Specialized in RF-Design. I had 6 Subjects with 4 different profs on system theory and software receiver design. Until i watched your video i did not really understood what this IQ modulation/demodulation is all about. But you just broke down 2 years of studying in just ~20 min. This video is absolute gold. Now i have an understanding of IQ modulation. Thank you sir!
Thank you! Maybe you should share my video with your professors!
I have never heard of a degree in electronical engineering. Maybe you mean electrical? Or electronics?
@@jeppe5942 there's always a first time to hear about something
Wow. I just finished reading the ARRL handbook on IQ modulation and walked away scratching my head. 20 minutes after playing start on this video cleared up all of my confusion. Very clear explanation and very well demonstrated. The examples are golden!
I‘m a beginner in „hobby RF“… and I understood IQ for the first time. Thank you for this great video!
Here is someone who really knows what he is talking about. So clear, so easy!
This always seemed to me like a complicated matter. Not anymore!
Thanks a million.
This is pure YT-Gold. Well prepared, nicely edited, good mix of theory and demo.
You just combined so many of my engineer classes I am rather stunned. I wont sleep tonight.....thanks.......
This is the best tutorial on IQ signals I’ve ever seen. You have clearly explained this topic that has always been very hazy in my mind.
I had more "ah-ha!" moments during the 20 mins of this video than I have during my entire 10 years in telco! Thank you so much for your sharing of knowledge. This is a great, "back to basics" instruction for anyone working with any type of RF signal. Thanks again, you got a subscribe from me!
Perhaps the best explanation for basic modulation & demodulation I've seen. Respect.
This is the most clearly explained (I & Q signals) I've ever heard since college. Thank You.
I know this is an old video but thank you for covering the foundational concepts of what I/Q data represents and showing exactly where the rubber meets the road. This information makes the more "sophisticated" topics more attainable. Thank you!
I bumped on this channel as I have to take over a RF testbench for infrared detectors during my PhD and this channel is completely what I need! Thanks! 🎉
This has been the most clear explanation of demonstration of IQ processing I have come across. Amazing content, thank you!
FINALLY - THANK YOU!
After years of working with Digital Video Signals for Satellites (DVB-S), I understood BPSK (flipping the carrier) modulation & vaguely understanding QPSK with the constellation diagram. Then came (DVB-S2) with 8PSK for HD & all I could manage was being able to regurgitate the BS I had been told. NOW, I finally get the nuts & bolts of how QPSK works, is assembled & deciphered, along with having a thorough understanding of QAM signals. From here I can extrapolate that for 8PSK & 16QAM. THANK YOU!
Thanks a lot - I just had the most valuable 20 Minutes of TH-cam-time since many years! They way you explain the concept us IQ modulation is perfect in its combination of simplicity and detail.
I recently started to work on digital designs for rf applications (mainly BT and WIFI) and this was the first time I fully understood that concept.
Impressively clear explanation covering all the major points without descending into nonsense. Bravo.
It is the most satisfying tutorial so far in my life, after working in Radio Resource Management for one of the leading telco for quite a long time for the first time I was able to visualize the IQ concept. Great work and your efforts are visible. You are simply awesome.
nice job, clearest and simples explanation of IQ signals in the whole internet
WELL DONE Alan ! You have once again taken a deep topic and presented it a form that is easily understandable. It conveys to the viewer a working overview of the theory that powers software defined radios. Thanks again
Your didactical skills, brought light to a rather complex topic!
Thank you very much for your great explanations and authentic demonstrations on your scope!
I've been exploring RF for a few months now and have watched countless videos on the topic. Your explanation of quadrature signals is easily the most complete yet simple to understand. My understanding of I & Q has just made a big leap
This is one of the best videos on TH-cam.
Thumbed up before watching. I know this is going to be amazing.
I was right.
So did I ))
Hey! Another one to the list
People need the concept illustration like this to have a solid foundation before they begin learning all the tedious and boring formulas derivation like those taught in schools . Great work for spelling it out to the world.
amazing ....for the first time in my little life i have understood what actually i was reading all my life....
thank you very much for this beautiful demonstration
5 min into the video and I already know I'm going to learn more here than an entire semester worth of college education. Plus looking at the comments of people with decades of experience saying this video helped them is a really re-assuring. I'm glad I found this while I'm still in college. I'm looking to build a career in this field and this will definitely be a stepping stone in the right direction. Thank you so much!
Excellent job on this. I've read several papers on this and finally absorbed it after about the 3rd one. Your practical approach using a scope to show the modulated signals in the time domain was a great way to tie it all together. Thanks for taking the time to put this together. No doubt that many will benefit from it. Thanks!
This is the best explanation of IQ signals ever. Still here 10 years later🔥🔥🔥
One of the best explanation ever, even for me that I am not native speakers, I am from Brazil. You have the ability to explain things in a simple way and make everything clear. Congratulations !
Thank you so much for this video. I can finally start to understand all the math that I have been doing blindly! You are a great teacher! Please never stop making amazing videos like this one.
excellent practical info. never seen something like this. clear diction , clear video , subject content has been delivered linearly . Great Job sir. Now I have to watch all your videos
Thank you Alan. This is a subject on which I was completely ignorant of aside of Grey code and in under 20 minutes I now have a basic understanding and a light bulb moment into understanding of a small telemetry modem I have.
The thing I like most about your channel is even within a fraction of all that is electronics related, you manage to create clear and concise educational videos every week. Such a pity the "biggest" electronics related channel has lately degenerated into a lifestyle show. In my opinion content older than say 2 years should not generate income for the "professional" content producers to prevent them from resting on their laurels. Your channel is all about discovery and questions of income never arise. Channels like yours are the reason why I now rarely watch TV.
Thank you! Very nice of you to say. I hope I can continue to put together content that people like yourself find interesting, educational and useful.
Alan. Extremely helpful video. Your description and graphics make understanding the subject much easier. Then when you put them on the scope, well that put it over the top. Seeing the signals on the scope tied all the elements together. Very much appreciate your educational videos. N2GMA
Wonderful video..never seen anyone explain IQ simpler than this…thank you professor !
I was just started to studying RF, and i watched so many videos but couldnt uderstand the IQ stuff , thanks to you i can move further, thank you so much sir, u really explained it very clearly.thanks again.
world needs more teachers like u ....thanks you for the video :)
Excellent! You have an unusually good combination of skills; that being the knowledge of the subject and the ability to present it clearly.
One of the best video tutorials on I/Q I've seen so far. Thank you :)
Thank you for the nice comment!
This is, without any doubt, hands down, the best explanation of quadrature signals that has ever been created anywhere, in any format, including world-class textbooks. You deserve respect.
+Bert Holtappels Thank you Bert, I'm glad that you enjoyed it.
Really great explanation!
Almost as good as Applied Science explanations.
Are you a teacher? You are better than many of them. Much respect, sir.
Thank you. No, I'm not a teacher, but I do a lot of training and explaining in my job as a field applications engineer for Tektronix.
+w2aew That was a small but great exposition. Thank you.
Wow, excellent tutorial. I never really understood phase shift keying, but you made it perfectly clear. I feel like I've progressed from the 20th century to the21st!
I'm glad this video helped you!
same here
I took the RF series at university and I learned so much more practical information from you in such a short period. It definitely helps at work and my ham knowledge.
Thank you for your nice comments - glad to know that my videos have helped.
Best I/Q mod/demod explanation I've came across in university and workplaces, so glad I stumbled upon this video in desperation of trying to understand I/Q. sub'ed.
Absolutely the best description of this seemingly complex subject. I worked as a video engineer for many years, and looked at these i/q signals on the scope without fully understanding them. My only wish is that you did a little more explanation of the demodulator side of the i/q signals in a receiver. I kind of get it, but would love, 10 years later, if you could help me with it!
Thank you so much, it's like a light bulb lit up for me. Thumbs up for production value and a quality video. 73, de N6HZ
Thank you, I'm glad you enjoyed it.
Same here, great video, thank you.
This is a perfect video which I will share with anyone who asks what IQ modulation is sir. Thank you.
Excellent explanation, I guess there is no point of college any longer for a self learner, just good text-books with TH-cam tutors like w2aew are more than enough to gain that precious knowledge.
totally agree
Excellent video, I stumbled across this accidentally but I've never heard anyone breakdown the I/Q mixing so well. Outstanding!
An American way of passing on information: simple, direct and easy to interpret.
Simply the best information you can find here on TH-cam.
This was the most instructional understandable tutorial I have seen. Very nice to visually see how this works. So very cool! Thanks you!
I wish I had you as my Electronics teacher..
great explanations and a great quality video
Fantastic video. I've searched through a few IQ explanations on youtube, but the manner in which you've laid this out makes it the first one to make it 'click' for me. The use of the oscope is inspired - it allows you to see the 'real time' changes, as opposed to videos that use demonstrations in pure software, which are often far less easy to grasp. I think I grasp IQ signals much, much better now. Thank you.
Excellent demystification of the concept.
W2AEW is always awesome. BTW, I was just watching this: Defcon 21 - All Your RFz Are Belong to Me - Hacking the Wireless World with Software Defined Radio . A long presentation, but some really good info and things I want to try out myself (measuring baudrate using gnuradio etc). If you haven't seen it already, you should!
--... ...--
There was an excellent free Coursera on-line course given by the DSP group at EPFL (Switzerland). I think they run it every year. Well worth doing to get a solid mathematical foundation on the topic. www.coursera.org/course/dsp
Hans Van Ingelgom Wow, he packed a lot of stuff in one talk.
I think that I didn´t learn this much in my class in whole course than this video... Thanks
the best of the best explanation i have ever seen about such a complex topic 🎩🎓
The best explanation I've heard so far. Great work!
Such an incredible well put together lesson. I'm just getting into EE and RF and these are the things I wish I asked my grandfather to teach me before he became unwell. He had a great mind for RF. Thank you sir!
Excellent explanation and demos!
Samy Kamkar lol, just watched one of your old conference in which you talk about signal modulations. Wanted to understand more about it and here I find you xD
So all the youtube stars watch Alan's IQ videos huh? :-P
Dude, you deserve a Nobel Prize in Teaching
Very well explained! I will share this to friends who are also interested.
I know this was posted 7 years ago, but I was really struggling to get this concept down and you helped me crack it (I think). Thanks so much!
As a CATV engineer I have to say this is one of the best short training videos that I've ever seen accurately describe QPSK/QAM. Thanks for putting this together! Do you have anything you can share concerning OFDM?
Also working in the CATV/QAM industry, I agree! R & S has some good videos too more recently.
Holy cow, that video just obliterated the last 1.5 years of my electronics education. Thanks a lot mate
I've become curious about SDR lately; you haven't thought about presenting a small SDR DIY project or something like that?
One question: for demodulating IQ, how do you know what phase is, well, zero? The phase-varying signal doesn't tell you by itself. For digital signals you could just let the transitions, rather than the levels, represent bits, but for analog signals wouldn't you need to know the "in-phase" time?
You generally don't need to know where "zero" is. You're really only interested in the changes. So your arbitrarily normalize at any point, and track variations from there. Amplitude as SQRT of sum of I squared and Q squared, phase as arctan(Q/I), and frequency as d(phase)/dt.
***** Very usful answer.
Love modulation demodulation videos. I did my Senior Project on Blind Signal Modulation Classification using Cyclo-Stationary and Cumulants analysis. I found I have a skill there, which now i am letting it die off as an IT. Seriously, engineering is the best place in the universe. It is a place for me because there is where i withdraw myself. Love seeing mixers churning signals out.
Alan, this is brilliant. A Ham University Professor!
I love this video with you clear and concise explanation and followed with a real life signal analysis on a test instruments. This makes your tutorial video worth a lot more than gold! As famous saying goes, "A picture is worth a lot more than words!" The signal theory, followed by how they interact with each other, the simple math and visual explanation of Phasor diagram. Concluding with explanation of the signal analysis on the scope, helps to expand the difficult subject in a clever and concise way for the novice. You did a very wonderful job and I love it! I have tried writing a procedure on this subject, for testing mixers. You did a great job with your explanation and video. Thank you!
Thanks! You might enjoy this video too:
th-cam.com/video/RHFZUqUM8DY/w-d-xo.html
w2aew do you take place in university? Your videos are very fluent and easy to understand, academical. You explain things in very clear and understandable way. Thumbs up!!
No, I am not a professor. Just a Field Applications Engineer, working for Tektronix.
From experience I can tell you, even on reputable universities you'd be hard pressed to find a professor that can explain his stuff that well.
***** I would like to hear you on The Amp hour. I would be interesting.
***** I *was* already on The Amp Hour, about 2 years ago. Here's the link:
www.theamphour.com/theamphour-117-undulating-utensil-utility/
Nice video. Although I am familiar with the subject, it is a pleasure to watch it. Thanks!
I always get an excellent education from your videos, hope one day to have a 1/4 of your knowledge.Thank you Alan for all that you give us.
So this is really fascinating, and I have a question. How in the world can you pull I & Q out of a waveform? How do you know what the phase offset is? How can you know if the phase is being modulated from 0 at all? You have a single waveform, how can you possibly know that it is the product of two waveforms. Example: I have a number, 45. Get the I & Q from that. Can you do it? Did I add 20 and 25? Did I add 1 & 44? did I add 0 & 45 or 45 & 0? You can't know! how can you pull I & Q out of a waveform unless you already know what I or Q are?
naikrovek The answer is - you don't *pull* I and Q out of a waveform. You *generate* I and Q by mixing the incoming signal with a pair of quadrature local oscillators. Phase becomes relative. Pick an arbitrary starting point, then observe how phase changes with respect to that point. Any difference in frequency between the incoming signal and the local quadrature oscillators will show up as phase rotation vs. time.
***** hi, Can you pls explain what you meant by phase being relative.
Just as I stated in the previous reply. There is no absolute phase reference point. So, you compute the phase via arctan(Q/I), pick a desired reference point and then measure phase changes relative to that user selected starting point.
***** Thanks. Yes you have stated below.
Fantastic video!!!! I really appreciate the work you put into building the physical mixers and demonstrating the modulation with your equipment there. I'm striving to understand how to modulate / demodulate signals, and this video just connected a LOT of dots. Thank you!
very nice && very informative .. Excellent effort ... Thank you
Brilliant people know how to simplify complex concepts and you just did that, thank you.
Excellent video. Thank you.
Thanks Alan, very nice video again. The words QUADRATURE AMPLITUDE MODULATION just lit up in front of my eyes. This is such a clean explanation.
This channel should have zillions of subscribers. Thanks for keeping at it. 73s EA5HZO
Hi ***** another awesome demystification for me, very easy to follow your explanation, definitely something interesting to play with. Thank you for posting. Gerry
THANK YOU!!! Really clear and finally understood wtf we were studying in uni during my bachelor's in RF. It's only now that it clicked that just like AM/FM/ASK and all the other modulation techniques what is the significant part of the carrier that we were changing.
Well done, "professor!" Was that an eevblog bumper sticker I spied? Wow, and afrotech is here too. We need a convention with Alan, Dave, Afro, and Mike. Now how cool would that be?
That was one of the EEVBlog PCB rulers on my bench, yes. It would be a lot of fun to get together with those wizards!
Add Gregory Charvat and Michael Ossmann to the reunion, too. The last episode of The Amp Hour (#214) was a mix of a lecture and brainstorm session; really good.
Alan, excellent video! As usual. Regards, CH!
I really enjoyed the last Amp Hour show too. We'd also have to add Chris, and don't forget Shahriar from The Signal Path Blog.
***** Sure! and Jeri Ellsworth too! Can you image all of you together? haha!
BTW, I am waiting for my Softrock Ensemble II receiver kit to arrive, and, ahh, I have just watched your video on the HotWheels radar analysis and my head is about to explode. Too muy IQ today!
Charlie Pechiar Agreed! I met Jeri once, by chance, at an airport. We were on the same flight. This was long before Technical Illusions and even before her time at Valve.
Wow, I just stumbled on the best TH-cam video I have ever seen for explaining a subject. I was looking for an explanation on QAM after watching a video about NTSC color data transmission, and how it is backwards compatible with black white televisions. The color data is hidden in the black and white compatible luminance stream, and extracted with QAM. Your explanation made it completely clear on a higher level, now it makes sense to me. I recalled doing the math in my signal theory class in college, but it never really made sense to me. Further, the basis of software defined radios makes so much more sense too. Thank you very much for this video.
OMG!! you are awesome!!!
Simple language , professionally explained in both sections theoretical as well as practical part…not a single word can be omitted…..superb..
Thank you sir
Why no one shows how to demodulate FM signals. I watched 10 videos and no one shows it, they just say its "easy". Well if its easy then they should show it.
Darko Bulatovic exactly. im in the same boat. it isnt clearly explained at all. it almost seems like 98% of the video is about how to modulate them, but only a brief description was given with demodulating them.
pepe6666 Given that the instantaneous phase is the arctan(Q/I), and that frequency deviation (dF) is simply the "rate of change of phase", then FM demodulation from IQ is traditionally done by taking the time-domain derivative of the phase. f(t) = d(arctan(Q/I))/dt. More details can be found here:
www.embedded.com/design/configurable-systems/4212086/DSP-Tricks--Frequency-demodulation-algorithms-
***** I could have swear that you had another video where you explained it. not 100% sure. I know I found it later somewhere.
+w2aew Darko Bulatovic Here is a circuit/blog I found that demodulates BPSK - I hope to give it a try. www.analogzoo.com/2014/12/amplitude-demodulating-bpsk31/
is this a proper method? (edit: trying to ref w2aew)
Raymond Tant There are many ways to do this, and this is certain one valid approach - fairly simple because it only relies on simple amplitude detection. This works OK on this waveform because the phase shift is well filtered, providing a well defined and easily detected dip in the amplitude as the phase is shifted. If the baseband signal was not low pass filtered so well, the amplitude dip would be a lot narrower and more difficult to detect this way.
What an excelent video to completely understand the concept of I & Q signals. Greetings from Buenos Aires, Argentina.
Your videos on IQ are great, I learned a few tricks and a new way of thinking about a few things that really cleared up a mess in my brain......I really learned more in a few videos than a year in school. Or at least you cleared up what i had had been missing. Thank you. All your videos are amazing. You make TH-cam a goldmine of valuable information.
Good one !!!
This and your video on the diode ring mixer have turned black magic into "Well that's simple!"
And don't be afraid to give us the math, that's what explains it all.
Thank you again. I was looking for an IQ explanation and when I found a video made by you, all my fears were vanished. I knew by the end of this video I would understand IQ signals, and that happened. All the best for you!
Excellent explanation. Awesome.
Well paced, clear, develops concepts and progresses logically, great scope shots, great diagrams. I learnt quite a bit. Thanks.
Clear explanation, thank you. Small adendum: at 5:45 when you make Q=0, the resultant shifts but also amplitude reduces to 1.
00:02 Basics of IQ Signals and IQ modulation & demodulation
02:16 Basics of IQ Signals and modulation
04:28 Varying I and Q components can lead to amplitude, frequency, and phase modulation
06:45 IQ modulation enables complex modulations through amplitude variation
09:08 Understanding IQ components in phasor diagram
11:28 Varying I or Q components between plus and minus 1 inverts the waveform.
13:50 Understanding the phase shifts in IQ signals and constellation points
16:17 IQ signals can represent any modulation type with appropriate generation of I and Q waveforms.
18:31 Understanding IQ signals and their role in modulation and demodulation.
Crafted by Merlin AI.
IQ Signals and IQ modulation explained in best possible way. Excellent video.
Best video on IQ modulation
Fantastic. I'm am experienced electronics engineer, but always thought I & Q was difficult, so never bothered trying to learn. Thank you very much
What a beautiful explanation and demonstration. So clear and interesting! Thank you for taking the trouble to do this.
The outstanding thing with w2aew, a complex subject of 1000 pages book, is understood in a few minutes.
one word Alan, you are Awesome.
This is the best tutorial on basic concept of Phase modulation and explanation about IQ samples. I would love to see similar content describing FFT, IFFT, IDFT concepts as well. Thanks for sharing knowledge.