Agree with the other commenters - really an excellent presentation of the material. Start with the goals, describe the circuit, and demonstrate the circuit. Where you go above & beyond is with the impairment demo. Just looking at the equations it is very difficult to visualize how the input impairments affect the modulated signal, but the demos make it crystal clear. Not just the "what" but the "why."
Within 14 mins, You have done the great job that others take 14 hours to do and still fuzzy. We should change our EE teaching and learning. We are wasting our time at uni's
Completely agree. It's sad that I'm having to supplement several semesters of EE education with Khan Academy and TH-cam (particularly w2aew), and I wasn't a bad student at all. I started college at the turn of the century, but still have to reinforce things like this all the time.
All those technical papers I've read on IQ modulation pale into the background after watching your TH-cam presentations on the topic of IQ systems. You have an incredible ability to communicate. Many thanks.
Rofea Optoelectronics offers a product line of commercial Electro-optic modulators, Phase modulators, Intensity modulator, Photodetectors, Laser light sources, DFB lasers,Optical amplifiers, EDFA, SLD laser, QPSK modulation, Pulse laser, Light detector, Balanced photodetector, Laser driver, Fiber optic amplifier, Optical power meter, Broadband laser, Tunable laser, Optical detector, Laser diode driver, Fiber amplifier. We also provide many particular modulators for customization, such as 1*4 array phase modulators, ultra-low Vpi, and ultra-high extinction ratio modulators, primarily used in universities and institutes. Hope our products will be helpful to you and your research.
Thank you for sharing your videos with all of us. I enjoy them very much. I must say, you folks are light years ahead of what I've learned in my day, but your topics always peak my interest whether I understand them or not. I always learn something new on your "Circuit Fun" videos.
This is amazing. Like many have said, you have made the concept very clear in 14 minutes that takes a lot of studying and still remain unclear!. Please continue making such videos.
@@Aemilindore That's a little unfair! The guys who teach it at Uni's have PhD's. They KNOW the theory very well, but what many CAN'T do is teach the practical aspects. Most of them have never practised as professional hands-on RF design engineers like Alan has.
@@hectorpascal Writing some equations on a board or presenting them on slides teach nothing to students. Professors do science. They must teach practicals. And frankly they want to. They just do not have the knowledge that Alan has in this field. Now, professors may know things about wireless that Alan doesn't. But about IQ, about modulation, Its Alan. A PhD is a qualification that says you know a very specific topic. Not an entire field. Alan's job is to engineer things. But this time, he takes a job of a professor. To teach. And about wireless communication, Alan does it the best. Imagine learning this from a university professor. It will be a series of trigonometry equations. HAHHA.
Hello, Thank-you so much for your great videos. I appreciate the time, effort, and remarkable expertise that you are sharing with the world. The combination of mathematical and lab-oriented presentation is amazingly lucid and easy to follow. Thanks again!
So glad to have you back. Hope you're feeling well. This is central to my interests, so you hit yet another home run as far as I'm concerned. Thanks! That was a great explanation.
Great clip again, Request: I guess the a whole clip should be devoted to impairments to IQ modulator, and another whole clip to single side band suppression test. Your clips are so good that I would recommend that you publish a book that each chapter associate with one clip that goes in more details, so that people watch the clips first and then read the chapter about that clip. I would be the first to buy a few of them and give to teenagers in my family and colleagues as a present, and keep a copy for myself.
I work with some very $ophisticated WLAN test equipment. Among other things, it can display I/Q diagrams and make Error Vector Magnitude (EVM) measurements. Sometimes the I/Q plots are very eye-popping, but trying to correlate the visually displayed phenomena back to the problem is very tough. Your video helps explain a lot of the effects I see, and gives me some good ideas. As always, a great video !
This is what I was looking for - for so long time. You hit right on the nail while most of other beat around the bush. Thanks a lot for such great videos.
Hay Alan Great very very clear in a simple way to understand, I remember looking at the same thing thru Reading the books about it got totally lost very confusing .You do a nice job delivering the explaining. Thats for your Efforts that you put forward. 73's Alan
Great video OM. Thanks, your explanations border on genius. Explaining such "complex" (sic) phenomenon is not so easy. 73 de KT1R / Lou in Bangor Maine Ex-HP tech support and application engineer
Ahhh...my brother John Eckert, no relation but we joked about it at S800 training every year. I retired in 2015 and enjoy hamming and staying healthy. TEK is lucky to have you!
Great video as always! Could you do a follow-up discussing carrier recovery in the context of demodulating IQ data? It seems like you would need to know (and phase lock to) the carrier frequency in order to distinguish the I and Q components. I couldn't find any simple resources out there that explain how this is done.
Sort of wish you were my Comm prof in my EE courses back in the 70's... Of course you'd have to make due with a lot less sophisticated equipment... Though a good indication of how good an EE lab was, was how many Tek 475 scopes it had...:) ... 73... Roger / NQ8RP
As always excellent video! It would be nice to see the receiver side of this qpsk signal and the effects that you mention on it (dc component, attn, etc)
Truly outstanding example and explanation, Professor W! You should present the math behind it, to show why IQ Modulation is used instead of AM+FM or AM+PM. ;>)
I've probably watched this video 20 times. Such a good video. I do have a problem though that I've asked many people at my work but none can answer me. At the nulls of the frequency spectrum I'm getting harmonics. So say my LO is 2Ghz and my I and q being fed are 20 MHz square waves. I get large harmonics at 2020, 2040, and 2060 etc. I dont see these in your video so I'm not sure where they are coming from in my setup. Again, absolutely love your videos, I wish I was taught this way in college.
@@w2aew the square waves do have a DC offset on them. they are balanced though, also I'm generating the square waves from an fpga and its psuedo random.
@@w2aew thanks so much for the replies I really appreciate it. I meant that the dc offsets are equal to each other on both the I and Q lines. I keep thinking this is some sort of symbol clock leakage or possibly the bit stream is not psuedo random but repeating some pattern.
Sir very informative video.Thank you so much. How to supress the Lower side band and upperside band using upconverter board to suppression the LSB and USB using 16 bit I/Q offset_adjust and LO amp I/Q
I'm curious what would happen if you used the I and Q inputs as Left and Right channels for audio, if the two channels would be clearly separated at the receiving end, or if it would just end up as a mixed together mono signal an both the I and Q output on the demodulator side.
Hi! Excellent video as usual! What would one use (circuit or IC) to generate quadrature signals other then quadrature hybrids (they seem pricei...). What would be a low cost alternative for not so precise applications?
There is a fairly common technique that is found in low-cost SDR radios that uses a 4x clock and some dividers to create a pair of quadrature clocks. See an example in this video: th-cam.com/video/BG0rmMGpwMc/w-d-xo.html
~ 12:00 how big is the phase shift we are seeing there? Also the DC offset and attenuation you put in... this would help to get a feeling how "perfect" the alignment of such things must be
Hey Alan, I would be glad if you could explain why LO for In-phase signal generator has dropped off its amplitude when you had applied non-zero I(t) signal. (4:00)
Modulation is used when you are going to transmit your signal through a long distance. If you want to send you baseband signal(i.e. signal without modulation with an antenna, you would need an antenna maybe a few kilo meters long). In this video, he demonstrates basically a few linear modulation methods. Pros: Simple to build. Cons: Less resistance to noise in channel.
What is the effect of the voltage level of the LO on the level of the output RF signal? What is a good level for the LO signal when compared to the I or Q signals?
The part that im still missing when demodulating is, how would you generate the LO signal? How do you lock into the incomming signal frequency, and know what phase angle your reference signal is at, compared to the recieved RF signal? Isn't that necessary to know, so the constellation diagram isn't shifted at the reciever, so you demodulate the wrong bit patterns?
I want to thank you for all of your videos on I Q modulation. I had a little trouble following your video #170 which is about demodulating IQ modulation. If you apply an AM signal to the input of a quadrature mixer such as the Minicircuits ZFMIQ-10M, would both the I and the Q outputs vary with the amplitude of the input signal. would the phase shift of the output signal be 45 degrees? I did not quite understand about the rotating vectors and the demodulation of a FM signal. I have a goal of understanding IQ modulation and then demonstrating some of your experiments for our local ham radio club. One question I have relating to this video is how to solder the the Minicircuits ADE-1ASK mixer to a circuit board. I don't have any reflow soldering equipment. Is it possible to demonstrate some IQ basics with just using a 2 channel DSO, a good signal generator, the Minicircuits ZFMIQ-10M and the Minicircuits ADE-1ASK, and a spectrum analyzer? Thank you, Rick Phillips
Yes, if you apply an AM signal to a quadrature demodulator, both the I and Q output will vary in amplitude. Phase between the I and Q outputs will be 90 degrees, due to the 90 degree phase of the LOs in the demodulator. I hand soldered the ADE-1ASK onto a small SMT breakout board from QRPme (qrpme.com/?p=product&id=MEP). Very easy to do - just solder one leg at a time. You're going to need a couple of generators - one at least for the LO input, and possibly another two for the I and Q inputs respectively.
Thank you. I was thinking of using the Minicircuits ZFMIQ-10M quadrature mixer to obtain the 10 mHz quadrature signal and then using the ADE-1ASK mixers, one on the I output of the ZFMIQ-10M and the other on the Q output of the ZFMIQ-10M. I would use a Wavetek (older) signal generator as the 10 mHz input to the LO of the ZFMIQ-10M. I would apply the input signal (RF input) of a variable signal generator to each of the ADE-1ASK s. I did not quite understand how to get the I and the Q vector lines that you obtained on your oscilloscope and how the vector lines rotate with a FM input. I think that I need to study a little more to understand about demodulating SSB signals. What inspired me to learn about IQ modulation and demodulation is that we have had several hams talk about SDR radio and IQ modulation, but with no real good explanation of how IQ modulation really works. I know and have several books about SDR, but these books are on an engineering level with complicated mathematics. I am now working on sharpening my math skills and concentrating on trig and complex numbers. I would just like to explain IQ modulation on an intuitive level and I would love to tinker with IQ modulation and demodulation. Thanks again. Rick Phillips
Question: As I understand it, demodulation requires not just the received signal, but also the original IQ signals (or at least one, as it's trivial to derive the other with a phase shift). Obviously this is not going to be available in most situations, so what is the practical solution to this problem?
Usually there is a unique data pattern in the transmitted data that is used by the receiver to establish the base phase of the signal. The receiver performs an IQ down-conversion and looks for the sync pattern in the n-number of possible constellation phase rotations.
Thanks for your time! You deserve the money paid to universities and lame textbook-only instructors! I’ve just learned in just 15 minutes what i couldnt learn 5 years engineering to get a degree called masters! You deserve a like and subscribe and more! Do you have any video about impedence matching necessary for rf amplifiers and filters. Keep up the good work ✌️
I know this is an old video... but if I'm building an IQ modulator for use on amateur radio bands, what is a good benchmark for "sufficient" carrier and sideband suppression? If I have -40dB carrier, and -50dB opposite sideband, is that "good", or do I need to do more work to make it better? Thanks!
@@w2aew Wow, thanks Alan, I appreciate it so much! This is such an amazing hobby, where people like you are actually accessible, and even reply to newbs like me. Thanks!
It is nice video hard concept explained nicely when you have explained with phasor diagram it is fully understandable about AM/fm modulation by i&q signals but when you have shown it on the oscillscope by saying frequency upset etc,it is not very clear by your demonstration . what is frequency upset_ and how mixer works in the oscillscope demo thank u
I think maybe you mis-heard me. At the end of the video, I am talking about frequency *offset*, not frequency _upset_, when referring to the sideband frequency with respect to the carrier.
W2AEW, thanks for these videos, they are very well put together and informative. Tell me this please: Have you ever heard the term "Universal Radio" when applied to IQ modulation/demodulation? Not as an "actual" radio, but a reference to the universal way that any signal type can be composed or decomposed by IQ analysis? I was sure I heard someone mention the term "Universal Radio", but I lost track of the reference.
I can understand why a SDR platform could be called a universal radio - because once you have the RF signal represented as IQ, you know everything you need to know to process that signal - at that point, it's just math....
Curiosity : what vector signal generator you used to generator digital signal? For I and Q inputs- thanks in advance for your reply. Also I believe that you used the same tektronix MDO4140C to generate 2 LO (Quadrature) input signals and monitor/display same 2 LO signals plus 3rd output modulated signal? Am I correct in my assumption
I used a Tektronix TSG4106A vector signal generator to get the I and Q signals. The 2 LOs were generated using a Tek AFG3252B 2-channel arbitrary function generator.
Hi Alan, Thanks for the excellent video, as always. I notice, at around 12.40mins (the ‘single sideband suppression test’), that you are supplying the Minicircuits ZFMIQ-10M IQ modulator with a positive frequency at baseband (i.e. an anti-clockwise-rotating IQ phasor), and at the RF output what you see is the LOWER sideband (LSB). So this module turns out by default to be spectrally-inverting. Is this normal default behaviour for such IQ modulators? I would have expected that, by convention, the designers of such devices would wish to make them non-inverting by default, as it would perhaps seem more logical. Regards, Damian (G4WPO).
While the paper showed that I applied COS and SIN to the I and Q respectively, the actual signals that I applied were actually reversed. I had put an annotation on the video in TH-cam, but YT removed the annotation feature and thus that note was lost.
@@w2aew Thanks for the response, although now that has thrown me somewhat, as I was expecting that the IQ mixer *WOULD* be spectrally inverting, whereas you’re saying that it isn’t. My reasoning for expecting spectral inversion is as follows:- imagine you have at complex IQ baseband a phasor with a low +ve frequency, starting with zero phase at 1+j0 (i.e. I=1&Q=0) and then gradually increasing in phase towards 0+j1 (i.e. I=0&Q=1) - i.e. gradually transitioning from pure I to pure Q. If you then think about what you would get out of the IQ modulator, it should start as cos(wt), when I=1&Q=0, and then gradually shift phase to end up at sin(wt) when I=0&Q=1. So at the end of this thought experiment the RF carrier phase is lagging by 90-degrees (w.r.t. the LO) what it was at the start (since sine lags cosine by 90-degrees), so the phase has been going in a -ve direction w.r.t. to the LO, or in other words the frequency at the RF output of the IQ modulator is slightly *LESS* than the LO. Hence a +ve frequency at complex IQ baseband has translated to a -ve frequency (w.r.t. the LO) out of the IQ modulator, or in other words the IQ modulator has created a spectral inversion at RF. At around 2 minutes into the video you describe an IQ modulator which you created yourself, which conforms to the paper diagram which you drew. Can you confirm that this homebrew IQ modulator is in fact spectrally inverting, as I have reasoned above?
@@w2aew Here's a nice tech note from Maxim, which I've just learned about, on the topic of inverting vs. non-inverting IQ modulators, which nicely sums up the whole issue: www.maximintegrated.com/en/design/technical-documents/tutorials/5/5499.html
Sorry about that - my site host changed the way these are indexed. Here's the correct link (also corrected above): www.qsl.net/w2aew/youtube/IQ_modulator_basics.pdf
Would it be possible to make a TH-cam on MSK and GMSK. This is used in DSTAR and I am having a difficult time finding how to homebrew a MSK modulator. I have replicated the information in this TH-cam and I now have a deeper understanding of IQ modulator basics. NICE JOB !! 73's Gene WB9COY
Excellent video !!! Been waiting for one like this for a while ? Do you have a vector network analyzer, specifically can you can make videos on how use the thing and why it has to be calibrated so many different ways and times.
Your videos are awesome as always. Can you make video about Light Modulation Photo Interrupter. It was invented by Sharp Japan (Model Example GP2A11) few years back. If you can explain how it actually works, That would be super awesome. Thanks
Looks to be some kind of modulated light source, and a receiver that looks for a reflected signal at the same frequency. If I even get my hands on one, I can do a video on it.
@@w2aew THE Q36 Space Modulator, of course. :-) By the way, thank you for all your videos. I'm nearing retirement and it is my intention to pick up my love for analog electronics. Your videos have helped remove a lot of the cobwebs from my days as a physics/electronics engineering major in college.
I did. I mentioned it right at the beginning of the video. Link is in the description. Here it is: th-cam.com/video/h_7d-m1ehoY/w-d-xo.html If you'd rather read about it, here's a blog I wrote: www.tek.com/blog/what%E2%80%99s-your-iq-%E2%80%93-about-quadrature-signals%E2%80%A6
is anyone willing to help me with a project with the I/Q Modulator? Would be awesome to find someone who has the knowledge and the fun to help me. 😆 (I‘m living in Germany)
As I progress through my life, I watch your IQ videos over and over again and I make more sense of my life.
My life doesn't always make sense, but these videos do!
Agree with the other commenters - really an excellent presentation of the material. Start with the goals, describe the circuit, and demonstrate the circuit. Where you go above & beyond is with the impairment demo. Just looking at the equations it is very difficult to visualize how the input impairments affect the modulated signal, but the demos make it crystal clear. Not just the "what" but the "why."
Within 14 mins, You have done the great job that others take 14 hours to do and still fuzzy. We should change our EE teaching and learning. We are wasting our time at uni's
Completely agree. It's sad that I'm having to supplement several semesters of EE education with Khan Academy and TH-cam (particularly w2aew), and I wasn't a bad student at all. I started college at the turn of the century, but still have to reinforce things like this all the time.
Well said Walid
"If you can't explain something simply, you don't understand it well enough"
I can't describe how much I enjoy in your videos. You explain in 10 minutes what our profesor is trying to explain for 2 weeks!
All those technical papers I've read on IQ modulation pale into the background after watching your TH-cam presentations on the topic of IQ systems. You have an incredible ability to communicate. Many thanks.
Rofea Optoelectronics offers a product line of commercial Electro-optic modulators, Phase modulators, Intensity modulator, Photodetectors, Laser light sources, DFB lasers,Optical amplifiers, EDFA, SLD laser, QPSK modulation, Pulse laser, Light detector, Balanced photodetector, Laser driver, Fiber optic amplifier, Optical power meter, Broadband laser, Tunable laser, Optical detector, Laser diode driver, Fiber amplifier. We also provide many particular modulators for customization, such as 1*4 array phase modulators, ultra-low Vpi, and ultra-high extinction ratio modulators, primarily used in universities and institutes.
Hope our products will be helpful to you and your research.
Thank you for sharing your videos with all of us. I enjoy them very much. I must say, you folks are light years ahead of what I've learned in my day, but your topics always peak my interest whether I understand them or not. I always learn something new on your "Circuit Fun" videos.
Cannot thank you enough for producing this educational excellence. Simply unparalleled!
This is amazing. Like many have said, you have made the concept very clear in 14 minutes that takes a lot of studying and still remain unclear!. Please continue making such videos.
Can't appreciate enough. No words to describe. if only they taught like that at universities.
They don't know this much, How could they teach like this?
@@Aemilindore That's a little unfair! The guys who teach it at Uni's have PhD's. They KNOW the theory very well, but what many CAN'T do is teach the practical aspects. Most of them have never practised as professional hands-on RF design engineers like Alan has.
@@hectorpascal Writing some equations on a board or presenting them on slides teach nothing to students. Professors do science. They must teach practicals. And frankly they want to. They just do not have the knowledge that Alan has in this field. Now, professors may know things about wireless that Alan doesn't. But about IQ, about modulation, Its Alan. A PhD is a qualification that says you know a very specific topic. Not an entire field.
Alan's job is to engineer things. But this time, he takes a job of a professor. To teach. And about wireless communication, Alan does it the best. Imagine learning this from a university professor. It will be a series of trigonometry equations. HAHHA.
You can use the SSB test as a reference to make the IQ modulator output more ideal by adding DACs and voltage sensors along the path.
Amazing video! Thanks for putting this together!
Hello, Thank-you so much for your great videos. I appreciate the time, effort, and remarkable expertise that you are sharing with the world. The combination of mathematical and lab-oriented presentation is amazingly lucid and easy to follow. Thanks again!
So glad to have you back. Hope you're feeling well. This is central to my interests, so you hit yet another home run as far as I'm concerned. Thanks! That was a great explanation.
Great clip again,
Request: I guess the a whole clip should be devoted to impairments to IQ modulator, and another whole clip to single side band suppression test.
Your clips are so good that I would recommend that you publish a book that each chapter associate with one clip that goes in more details, so that people watch the clips first and then read the chapter about that clip.
I would be the first to buy a few of them and give to teenagers in my family and colleagues as a present, and keep a copy for myself.
I work with some very $ophisticated WLAN test equipment. Among other things, it can display I/Q diagrams and make Error Vector Magnitude (EVM) measurements. Sometimes the I/Q plots are very eye-popping, but trying to correlate the visually displayed phenomena back to the problem is very tough. Your video helps explain a lot of the effects I see, and gives me some good ideas. As always, a great video !
Thanks, I always learn something from your videos. Re-watching #170 got me to move a step ahead in my understanding of I and Q mod/demod.
Excellent demo of the IQ modulator concept.Thank you very much.
thank you
This is what I was looking for - for so long time. You hit right on the nail while most of other beat around the bush. Thanks a lot for such great videos.
Hay Alan Great very very clear in a simple way to understand, I remember looking at the same thing thru Reading the books about it got totally lost very confusing .You do a nice job delivering the explaining. Thats for your Efforts that you put forward. 73's Alan
Well Done! This is some great stuff. All RF engineer should watch this...
Excellent explanation with great practical demonstration. As always, thanks for your videos.
Alan congratulations this is amazing video in 14 minutes.
Great video OM. Thanks, your explanations border on genius. Explaining such "complex" (sic) phenomenon is not so easy. 73 de KT1R / Lou in Bangor Maine Ex-HP tech support and application engineer
Thank you Lou - much appreciated - especially from a fellow AE (except I'm with Tektronix). Are you any relation to John K2OX (also Keysight AE)?
Ahhh...my brother John Eckert, no relation but we joked about it at S800 training every year. I retired in 2015 and enjoy hamming and staying healthy. TEK is lucky to have you!
I truly appreciate and enjoy your videos. Thank you for making things so easy to understand :)
Thanks for explaining this stuff properly.
Another incredible video. You are an excellent instructor. Thanks.
Great video as always! Could you do a follow-up discussing carrier recovery in the context of demodulating IQ data? It seems like you would need to know (and phase lock to) the carrier frequency in order to distinguish the I and Q components. I couldn't find any simple resources out there that explain how this is done.
Sort of wish you were my Comm prof in my EE courses back in the 70's... Of course you'd have to make due with a lot less sophisticated equipment... Though a good indication of how good an EE lab was, was how many Tek 475 scopes it had...:) ... 73... Roger / NQ8RP
Awesome video!!! Thanks so much for taking the time to make these. I always learn so much so fast!
As always excellent video! It would be nice to see the receiver side of this qpsk signal and the effects that you mention on it (dc component, attn, etc)
Thanks for this knowledge transfer
I would be interested in seeing a video like this one but IQ demodulation using this IQ mixer.
Truly outstanding example and explanation, Professor W! You should present the math behind it, to show why IQ Modulation is used instead of AM+FM or AM+PM. ;>)
Thank you Scott. As for the math.. ...gee, I have to leave *something* for the viewer to do!
This is pure gold!
Outstanding video Alan - thanks. 73, Bill KC5SB.
I've probably watched this video 20 times. Such a good video. I do have a problem though that I've asked many people at my work but none can answer me. At the nulls of the frequency spectrum I'm getting harmonics. So say my LO is 2Ghz and my I and q being fed are 20 MHz square waves. I get large harmonics at 2020, 2040, and 2060 etc. I dont see these in your video so I'm not sure where they are coming from in my setup. Again, absolutely love your videos, I wish I was taught this way in college.
Depends on the design of the mixers. Also can depend on whether the 20MHz squarewaves have a DC offset on them, or are they balanced around ground.
@@w2aew the square waves do have a DC offset on them. they are balanced though, also I'm generating the square waves from an fpga and its psuedo random.
@@slothluvschunk2301 If they have a DC offset (i.e. they run from 0V to xxV), then they are not balanced around ground.
@@w2aew thanks so much for the replies I really appreciate it. I meant that the dc offsets are equal to each other on both the I and Q lines. I keep thinking this is some sort of symbol clock leakage or possibly the bit stream is not psuedo random but repeating some pattern.
Sir very informative video.Thank you so much. How to supress the Lower side band and upperside band using upconverter board to suppression the LSB and USB using 16 bit I/Q offset_adjust and LO amp I/Q
Using the python GUI Interfaces
Thank you very much for making this video.
Thank You best explanation I got so far. Love it....
My IQ modulator uses beer and coffee.
I'm curious what would happen if you used the I and Q inputs as Left and Right channels for audio, if the two channels would be clearly separated at the receiving end, or if it would just end up as a mixed together mono signal an both the I and Q output on the demodulator side.
Clear as always, thank you.
beautiful scope
Hi! Excellent video as usual! What would one use (circuit or IC) to generate quadrature signals other then quadrature hybrids (they seem pricei...). What would be a low cost alternative for not so precise applications?
There is a fairly common technique that is found in low-cost SDR radios that uses a 4x clock and some dividers to create a pair of quadrature clocks. See an example in this video: th-cam.com/video/BG0rmMGpwMc/w-d-xo.html
Fantastic explanation. Thank you so so much
~ 12:00 how big is the phase shift we are seeing there? Also the DC offset and attenuation you put in... this would help to get a feeling how "perfect" the alignment of such things must be
DC offset was about 50-100mV out of the 400-500mV IQ amplitude. Phase shift was 10-20 degrees off of 90.
Hey Alan, I would be glad if you could explain why LO for In-phase signal generator has dropped off its amplitude when you had applied non-zero I(t) signal. (4:00)
Because it changes the bias on the diodes in the mixer, thus changing (lowering) the input impedance of the LO port.
I'm not as familiar with the digital modulation methods, can you discuss the uses and pros/ cons of this modulation method?
Modulation is used when you are going to transmit your signal through a long distance. If you want to send you baseband signal(i.e. signal without modulation with an antenna, you would need an antenna maybe a few kilo meters long). In this video, he demonstrates basically a few linear modulation methods. Pros: Simple to build. Cons: Less resistance to noise in channel.
QPSK is an expection. It's a non-linear modulation.
awesome content as always.
and man, that is a beautiful scope
What is the effect of the voltage level of the LO on the level of the output RF signal? What is a good level for the LO signal when compared to the I or Q signals?
The part that im still missing when demodulating is, how would you generate the LO signal? How do you lock into the incomming signal frequency, and know what phase angle your reference signal is at, compared to the recieved RF signal? Isn't that necessary to know, so the constellation diagram isn't shifted at the reciever, so you demodulate the wrong bit patterns?
Great video, thanks!
Another masterpiece. Thanks!
Thanks for this amazing explanation! and... could you please make a vídeo of a modified IQ modulator for a 8VSB transmision?
Simply wow!
Gorgeous video 😍😍😍
I want to thank you for all of your videos on I Q modulation. I had a little trouble following your video #170 which is about demodulating IQ modulation. If you apply an AM signal to the input of a quadrature mixer such as the Minicircuits ZFMIQ-10M, would both the I and the Q outputs vary with the amplitude of the input signal. would the phase shift of the output signal be 45 degrees? I did not quite understand about the rotating vectors and the demodulation of a FM signal. I have a goal of understanding IQ modulation and then demonstrating some of your experiments for our local ham radio club. One question I have relating to this video is how to solder the the Minicircuits ADE-1ASK mixer to a circuit board. I don't have any reflow soldering equipment. Is it possible to demonstrate some IQ basics with just using a 2 channel DSO, a good signal generator, the Minicircuits ZFMIQ-10M and the Minicircuits ADE-1ASK, and a spectrum analyzer? Thank you, Rick Phillips
Yes, if you apply an AM signal to a quadrature demodulator, both the I and Q output will vary in amplitude. Phase between the I and Q outputs will be 90 degrees, due to the 90 degree phase of the LOs in the demodulator. I hand soldered the ADE-1ASK onto a small SMT breakout board from QRPme (qrpme.com/?p=product&id=MEP). Very easy to do - just solder one leg at a time. You're going to need a couple of generators - one at least for the LO input, and possibly another two for the I and Q inputs respectively.
Thank you. I was thinking of using the Minicircuits ZFMIQ-10M quadrature mixer to obtain the 10 mHz quadrature signal and then using the ADE-1ASK mixers, one on the I output of the ZFMIQ-10M and the other on the Q output of the ZFMIQ-10M. I would use a Wavetek (older) signal generator as the 10 mHz input to the LO of the ZFMIQ-10M. I would apply the input signal (RF input) of a variable signal generator to each of the ADE-1ASK s. I did not quite understand how to get the I and the Q vector lines that you obtained on your oscilloscope and how the vector lines rotate with a FM input. I think that I need to study a little more to understand about demodulating SSB signals.
What inspired me to learn about IQ modulation and demodulation is that we have had several hams talk about SDR radio and IQ modulation, but with no real good explanation of how IQ modulation really works. I know and have several books about SDR, but these books are on an engineering level with complicated mathematics. I am now working on sharpening my math skills and concentrating on trig and complex numbers. I would just like to explain IQ modulation on an intuitive level and I would love to tinker with IQ modulation and demodulation. Thanks again. Rick Phillips
I think you need a ZFMIQ-10D *Demodulator* to give you the I and Q signals, not a ZFM-10M.
Okay, Thank you.
Fantastic video 👍
Excellent thank you for this
Question: As I understand it, demodulation requires not just the received signal, but also the original IQ signals (or at least one, as it's trivial to derive the other with a phase shift). Obviously this is not going to be available in most situations, so what is the practical solution to this problem?
Usually there is a unique data pattern in the transmitted data that is used by the receiver to establish the base phase of the signal. The receiver performs an IQ down-conversion and looks for the sync pattern in the n-number of possible constellation phase rotations.
Brilliant as always.
Thanks for your time! You deserve the money paid to universities and lame textbook-only instructors! I’ve just learned in just 15 minutes what i couldnt learn 5 years engineering to get a degree called masters! You deserve a like and subscribe and more! Do you have any video about impedence matching necessary for rf amplifiers and filters. Keep up the good work ✌️
I have a few videos on impedance matching. Here's one: th-cam.com/video/IgeRHDI-ukc/w-d-xo.html
Love these videos!
Very good one.
I know this is an old video... but if I'm building an IQ modulator for use on amateur radio bands, what is a good benchmark for "sufficient" carrier and sideband suppression? If I have -40dB carrier, and -50dB opposite sideband, is that "good", or do I need to do more work to make it better? Thanks!
That seems pretty good, the rest can be done with filtering...
@@w2aew Wow, thanks Alan, I appreciate it so much! This is such an amazing hobby, where people like you are actually accessible, and even reply to newbs like me. Thanks!
It is nice video hard concept explained nicely when you have explained with phasor diagram it is fully understandable about AM/fm modulation by i&q signals but when you have shown it on the oscillscope by saying frequency upset etc,it is not very clear by your demonstration . what is frequency upset_ and how mixer works in the oscillscope demo thank u
I think maybe you mis-heard me. At the end of the video, I am talking about frequency *offset*, not frequency _upset_, when referring to the sideband frequency with respect to the carrier.
Excellent!
Thanks Chris!
W2AEW, thanks for these videos, they are very well put together and informative. Tell me this please: Have you ever heard the term "Universal Radio" when applied to IQ modulation/demodulation? Not as an "actual" radio, but a reference to the universal way that any signal type can be composed or decomposed by IQ analysis? I was sure I heard someone mention the term "Universal Radio", but I lost track of the reference.
I can understand why a SDR platform could be called a universal radio - because once you have the RF signal represented as IQ, you know everything you need to know to process that signal - at that point, it's just math....
Curiosity : what vector signal generator you used to generator digital signal? For I and Q inputs- thanks in advance for your reply.
Also I believe that you used the same tektronix MDO4140C to generate 2 LO (Quadrature) input signals and monitor/display same 2 LO signals plus 3rd output modulated signal? Am I correct in my assumption
I used a Tektronix TSG4106A vector signal generator to get the I and Q signals. The 2 LOs were generated using a Tek AFG3252B 2-channel arbitrary function generator.
w2aew thank you soo much Alan 👍🏻😄
dude. how can I get in touch with you? I wanna be your PhD/fellowship student. your laboratory skills are amazing.
Well, if you're going for your PhD, you'll have to teach me! I only have a BSEE... ;-), and about 40yrs experience.
You are simply awesomeeee
Hi Alan, Thanks for the excellent video, as always. I notice, at around 12.40mins (the ‘single sideband suppression test’), that you are supplying the Minicircuits ZFMIQ-10M IQ modulator with a positive frequency at baseband (i.e. an anti-clockwise-rotating IQ phasor), and at the RF output what you see is the LOWER sideband (LSB). So this module turns out by default to be spectrally-inverting. Is this normal default behaviour for such IQ modulators? I would have expected that, by convention, the designers of such devices would wish to make them non-inverting by default, as it would perhaps seem more logical. Regards, Damian (G4WPO).
While the paper showed that I applied COS and SIN to the I and Q respectively, the actual signals that I applied were actually reversed. I had put an annotation on the video in TH-cam, but YT removed the annotation feature and thus that note was lost.
@@w2aew Thanks for the response, although now that has thrown me somewhat, as I was expecting that the IQ mixer *WOULD* be spectrally inverting, whereas you’re saying that it isn’t. My reasoning for expecting spectral inversion is as follows:- imagine you have at complex IQ baseband a phasor with a low +ve frequency, starting with zero phase at 1+j0 (i.e. I=1&Q=0) and then gradually increasing in phase towards 0+j1 (i.e. I=0&Q=1) - i.e. gradually transitioning from pure I to pure Q. If you then think about what you would get out of the IQ modulator, it should start as cos(wt), when I=1&Q=0, and then gradually shift phase to end up at sin(wt) when I=0&Q=1. So at the end of this thought experiment the RF carrier phase is lagging by 90-degrees (w.r.t. the LO) what it was at the start (since sine lags cosine by 90-degrees), so the phase has been going in a -ve direction w.r.t. to the LO, or in other words the frequency at the RF output of the IQ modulator is slightly *LESS* than the LO. Hence a +ve frequency at complex IQ baseband has translated to a -ve frequency (w.r.t. the LO) out of the IQ modulator, or in other words the IQ modulator has created a spectral inversion at RF. At around 2 minutes into the video you describe an IQ modulator which you created yourself, which conforms to the paper diagram which you drew. Can you confirm that this homebrew IQ modulator is in fact spectrally inverting, as I have reasoned above?
@@damianbevan5967 yes
@@w2aew That's great. Thanks.
@@w2aew Here's a nice tech note from Maxim, which I've just learned about, on the topic of inverting vs. non-inverting IQ modulators, which nicely sums up the whole issue: www.maximintegrated.com/en/design/technical-documents/tutorials/5/5499.html
Nice video, very instructive..
Hello again the notes link isn’t working, very nice tutorial.
Sorry about that - my site host changed the way these are indexed. Here's the correct link (also corrected above):
www.qsl.net/w2aew/youtube/IQ_modulator_basics.pdf
Would it be possible to make a TH-cam on MSK and GMSK. This is used in DSTAR and I am having a difficult time finding how to homebrew a MSK modulator. I have replicated the information in this TH-cam and I now have a deeper understanding of IQ modulator basics. NICE JOB !! 73's Gene WB9COY
Thank You best explanation .
Excellent video !!! Been waiting for one like this for a while ? Do you have a vector network analyzer, specifically can
you can make videos on how use the thing and why it has to be calibrated so many different ways and times.
I do have a VNA here. That is a good topic, I'll add it to my list.
Hi, good explanation.
High quality content!
Please make a video on homodyne mixer (Direct Conversion Reciever)
PLS make a video about OFDM and COFDM
I'll add that to my long list.
Could you make an amplifier without 1/f noise by tapping a standing wave controlled like that?
Please make a video on Tayloe mixers.
I've covered that a little on one or two of my SDR videos, like this one:
th-cam.com/video/BG0rmMGpwMc/w-d-xo.html
well done!
If only you could be my college Prof...
Quality videos
Thank you!
Your videos are awesome as always. Can you make video about Light Modulation Photo Interrupter. It was invented by Sharp Japan (Model Example GP2A11) few years back. If you can explain how it actually works, That would be super awesome. Thanks
Looks to be some kind of modulated light source, and a receiver that looks for a reflected signal at the same frequency. If I even get my hands on one, I can do a video on it.
w2aew Thanks for quick response.
So does the same thing happen with two square waves, 90 degrees apart?
Yes, there will just be more harmonics involved.
If I could give you 2 thumbs up, I would!
Can you make a tutorial about design and measurements of quadrature hybrid RF phase shift network, please?
typing w/ my feet. hands are busy clapping
Ok,I get it now...subbed :)
Is that a Q36?
What's a Q36?
@@w2aew THE Q36 Space Modulator, of course. :-) By the way, thank you for all your videos. I'm nearing retirement and it is my intention to pick up my love for analog electronics. Your videos have helped remove a lot of the cobwebs from my days as a physics/electronics engineering major in college.
I dunno crap about iq stuff, just gave a line and left for great work 👍
is it easy for you to make an IQ teaching video? :p
I did. I mentioned it right at the beginning of the video. Link is in the description. Here it is:
th-cam.com/video/h_7d-m1ehoY/w-d-xo.html
If you'd rather read about it, here's a blog I wrote:
www.tek.com/blog/what%E2%80%99s-your-iq-%E2%80%93-about-quadrature-signals%E2%80%A6
👍🙏💖
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is anyone willing to help me with a project with the I/Q Modulator? Would be awesome to find someone who has the knowledge and the fun to help me. 😆 (I‘m living in Germany)