This is so incredibly cool. This stuff is becoming a lost art. I got an EE degree in the early 80's but in my career I worked on the physics of solid state devices, so never used and quickly forgot the type of stuff your videos are about. I am eager now in retirement to go back and relearn this stuff I consider to be "classic" electrical engineering. Today so much is digital work driven by huge simulation programs that few really know this lost art. I am drooling over your scopes and test equipment. Thanks for the wonderful videos.
I'm an analog guy at heart, so my videos focus mainly on these topics. And, since I work for Tektronix, I have great access to wonderful equipment, which really helps in the videos.
Far from a lost art, SDR radios using IQ modulation and demodulation are proliferating. Real world use is driving increasing interest. I'm a licensed amateur radio operator and I now have several SDR receivers, two SDR transceivers and my analog transceiver has an IF tap for I/Q demodulation to monitor a wide swath of a band.
I concur with your point. My career mainly involved ABB Distributive Control Systems with 4-20 mA I/P valve controllers (current to Pneumatic) and Rosemount transmitters. After so many years of that, my understanding of the subject of many of these videos has atrophied completely. It's nice in retirement to get back to communication electronics. By the way Paul, I've enjoyed your videos very much, especially the two Arduino courses and the Learn Fusion 360 or die trying!!! God Bless my friend.
I'm sat here wondering why you're not my comms lecturer, or why I'm not taught like this at university. Simple topics are overly complicated for students for some reason. I've learnt and understood so much in 15 minutes compared to hours of lectures
The problem is really that these people fall into an annual syllabus and come up with a standard set of teaching materials. If you understand it at first pass great, you are the lucky one. The difference here is clear, if you love the subject you'll generally be a great teacher. Far too many teachers just don't love it, it's a day job
The real problem is that in most Universities there are very few good "teachers"! Probably 70% of the Lecturers/Professors are first and foremost "researchers". They devote the majority of their time to publishing papers to get grants (and by that to also advance their careers). When you can find a good researcher who is a great teacher too, you've struck gold!
Yeah, I guess the concept that is missed in universities is "abstraction level"... Before digging into mathematical treatment one should first show what those things even are! After all, all that knowledge actually emerged from these natural, organic concepts and relationships.
why were you not my professor, I can understand you, you make sense and "speak" English not sure what my professor spoke, His native tong was confusing language. I am just too overjoyed at your videos, what a mental relief to finally understand stuff . You're a Ham . Communications guys we have a Power company were I work, and my professor at college could use a lesson from you. You really know how to teach. Forever grateful to you deep kindness. You use great tools like your scopes and mixers to put it all together, a visual picture is worth millions. best 73s Mike wb7qxu
I feel like you should be accredited and I should be able to gain credits toward a Bachelor of Science degree having watched only a few of your videos! I wish you were running our labs at DeVry in Woodbridge NJ back in the late 80's! :) .... but seriously this is how every engineering classroom should be taught! Hand's on in the lab side by side with the theory!
there's a trend here of old 80s guys re-learning what they forgot (I'm one). I worry about kids of today and I am hopeful that SDR may play some role in re-igniting interest because a computer is involved and kids love them
I came here expecting a modulation demo. Took me a while to realise that you were demonstrating AM and FM demodulation setups, because I foolishly hurried pass the important details in the intro. Had to re-watch it over a few times to pickup my mistake, now the vector traces on the scope all make sense! Thanks so much for all the effort you put into these tutorials.
The phasor diagram, especially as you displayed on your scope, visually ties it all together for me. Great job as always! A video on the math used in designing the double ring mixer would be very informative.
I found these tutorials after trying to understand what the I/Q inputs and outputs on a K3 radio were all about. Thanks for a very easy to understand presentation. This also helps me to wrap my brain around the analog world of voltage and current relationships in a L/C circuit and Antennas!
By far the best lectures over the entire channel!! Wish that my teacher was at least half as good as you are when he tried explaining quadratures 35yrs ago! - Fortunately the books were better. (No internet that time.) Very clear communication skills, perfect and simple demonstrations, excellent job! Thanks for sharing and spending your time making these videos!! - This is what internet is all about. 👍👌
Awesome video! We just did a project in school, in a signal processing course, where we sent a digital message over an audio channel, using OFDM and QPSK. It is an interesting subject, thank you for sharing your knowledge!
Your short 'Lab' lessons (theory and practice) really inspire me (every time) to go and to build it myself right away 🙂...and to learn more on the subject. Thanks for that 👍
Thank you for making such a great, absolutely amazing, a documentary video about IQ signals. If anyone asks what the heck is i and q, this video (1-2) answers it totally.
Wow! A few years ago, I took a communications course that covered this material... I was able to get through all the mathematics, but I never quite "got it". Seeing your examples displayed on the scope really made it all click for me. Thanks!
Hi, Alan. :-) Always great to watch you videos for they are accurate, polite, and easy. Thank you. PS. I have an idea to design a sort of "direct conversion superhet": 45MHz 1st IF (I have a pair of 4520D crystal filters) then a simple LC or RC phase shifting network and an IQ product detector. It looks like your diagram for SSB generation, but IF input instead of Audio input. Yes, I'm trying to avoid building a polyphase network for I have no proper parts for that. :-) I can control it with a single si5351a (one channel for 45.1MHz...75MHz VFO and two channels for 45MHz quadrature BFO). Advantages: no mirror image while no polyphase network, no parasitic radiation, no BPFs - just 30MHz LPF, not much of relays and switches, microcontroller (I have STM32F103, STM32F303 and ESP32) can be used as DSP to code digital AF filters. Disadvantages: a noisy MC and si5351, high IF, high current consumption, need in 12V power supply (for I have no low voltage parts for 45MHz). What do you say? :-)
So basically it will represent nicely Lissajous curves if you mix AM with FM modulation in different ratio for a continuous signals and dots for a discreet signals. Nice explanation.
Very nice demonstration. Looking forward for future parts explaining frequency domain correlation with used modulation. Deviation, modulation index, gaussian FSK shaping, spectral efficiency etc. GJ!
Great clip again: In Injection locking two oscillators , at the same frequency, are used to create oscillation with much lower phase noise. I guess we can use your method ( IQ FM de-modulator with an X-Y oscilloscope) for checking how good the two oscillator are locked.
Excellent tutorial as always! Now it's all clear for me about IQ method for FM/AM modulation. Please keep it going. I'd like to see more SDR related tutorials from you. Could you provide me an information where I can find more useful materials about SDR?
Thanks for taking the time to make these videos. You do an excellent job of visually explaining these concepts. Keep up the good work! I'm learning a lot from you.
Once again - brilliant. Thank you very much! Love it! I'm just at a lost why anyone can give this a thumbs down. Do you know if the devil watches youtube? I thought he was too busy playing foosball.
You sir are a true scholar, keep up the good work! On a related note to FM, could you identify how incidental FM creates unbalanced sidebands on an AM signal?
chris kaplan Hmm - I never looked at that. I would suspect that it would be caused by a phase inversion of the lower sidebands on FM, partially cancelling the AM LSB. Certainly worth looking at...
Like everyone else here I very much appreciate your videos, they're brilliant thank you! Have you done a video explaining how a receiver locks its frequency/phase reference to the intended phase of the incoming signal? I struggle to understand how the receiver knows what is considered 0 phase shift for it to then determine deviations from that?? In this video you phase lock the sig gens together but how do remote receivers achieve this? Thanks again, I'm very grateful for your work.
Most commonly this is done by using a specific "sync pattern" in the data transmission - the rx looks for this sync pattern at the various phase rotations, then will use the phase rotation that properly decodes the sync word.
@@w2aew Ah I see! And is the sync pattern then broadcast periodically to keep everything aligned and prevent drift? Amazing, thank you. That was one of the last pieces of the puzzle I needed to grasp concept of IQ modulation - since essentially, they are all exactly the same sinusoids if you have nothing to reference them against right!? Much obliged to you, Thanks again for the videos.
I know the new QCX transcievers use IQ for it's mod/demod so was interested in learning more. As always excellent theorotical examples but some practical examples would be very helpful. For instance in the past two videos you talk about input and the resulting outputs (either direction) but not how to use those in a radio to actually transmit or receive something. Reminds me of my first physics classes. We learned all this theory and I thought yeah so what? In later years we actually did practical experiments to show the concepts in physics and I thought "Eureka" that's what it's all about!
You should make a video explaining the mixer and signal generator setup. That would help us to know, how to interface signal generators and mixer chip sets
It's going to take a few replays for this to sink into my old brain. But I do remember the phase method of SSB generation. The HealthKit Apache transmitter SSB adapter used phasing to produce the single sideband from the AM signal.
I too would like to do this experiment at the lab. Could you Please tell me where I can get those multipliers and signals splitters from? Your video actually persuaded me to try this on my own! you are truly an inspiring person.
The multipliers are simply ADE-1ASK mixers from Mini-Circuits. The splitter is a junkbox resistive splitter. You can also get an appropriate resistive RF splitter from Mini-Circuits.
Thank you so much. And thanks a lot for this great videos on IQ. its my second day going through them and trying to understand them. Each time, I learn something new.
5:00 Amplitude is just a factor of the radius. A phase is a delay or the opposite of "going around" like the first circle (the circumference.) I guess we can have 2 phases. 1 in the x and one in the y calculation. Maybe 3D applies sometimes. I'm just speaking from geometry and not sure how far the "phase" goes for the names on things.
Amazing video! I was wondering, is there a different method for working with frequency modulation, i.e. FSK (besides segmenting the constellation diagram as with PSK), because I imagine it would be difficult to determine the "rate of rotation" of your phasor vector in order to determine the frequency at a particular time. Might there be some Fourier transforms involved?
The mixers used here are simply the classic diode ring mixers. These are MiniCircuits ADE-1ASK, only because that's what I had on hand. You can build them yourself as shown in this video: How a Diode Ring Mixer works | Mixer operation theory and measurement
Very nice. Just some questions. How does the reciever know the absolute phase and amplitude of the transmitter? Is the information encoded in absolute phase or in differential phase shift? How does the LO of the Reciever "lock in" on the base frequency and of the transmitter's LO or doesn't it need to? I mean, I only have one antenna and if I flip it upside down my phase shifts 180. I mean I have to cross correlate to a second input or encode/decode in the phase differential of the frequeny,right?
The receiver doesn't know the absolute phase. So, typically one of two things are done. Data is encoded differentially as you suggested, or (more commonly) the data contains a specific sync sequence that is properly decoded only at one of the possible phase rotations. The receiver demodulates the data, looking for this sync sequence to establish the reference phase, then decodes the rest of the transmission using this phase reference. Often, there is a small frequency offset too, so the receiver will also compensate for that too (de-rotating the vector).
Thank you. I did not know that. I know the basic math of it but not the real world implementation. Can you do a video on how the synchronisation works? And on QAM.How does the QAM reciever know how to scale the amplitude? Why is the QAM diagram square and not circular? Also,I find your videos informative and well made. What I especially remember is learning about how diodes can be RF switches and how the diode ring mixer is just an assembly of switches. I did not know diode mixers operate in non linear mode,making them square wave sensitive.
QAM constellations are usually square because the I and Q signals are typically matched in amplitude to make it easier to null the Carrier feedthru (null DC offset).
Nice video on explaining FM using phasor method. As one more step further, how to explain the nulling of carrier in FM modulation for a certain FM deviation and modulation frequency using the phasor method? I know the Bessel function can describe it, is there an intuitive way to explain it using the phasor method?
How long did it take you to produce that video? There is so much information at any given point, it is really well structured. Setting up those demos, drawing diagrams and later edit/cut all the footage... I bet it would take me 3 days to shoot that video, even if I had all the instruments and tools!
This one took the better part of 3 hours. You're right, some of them take days to do, including setup, drawings, building, testing, shooting and editing.
I love your presentations and I am really thankful for what you shared. Angle increment is uniform in AM so the phase is actually constantly incrementing. This is what makes unmodulated carrier. Am I right? :)
Continuously rotating phase indicates an off-center carrier. AM is the modulation of the length of the vector formed by the IQ components. If they don't rotate, that means the carrier is at the center frequency.
For a vector with constant amplitude and no phase (angle) increment the I and Q would be constant and therefore just make a DC signal. The vector must rotate at constant angular velocity to create carrier. Therefore phase increments. Or do you assume here that IQ plane rotates while vector may stay in place as some authors do? In 6:26 it should be said that how fast this vector spins around equals to signal (carrier) frequency. Change in speed of spinning makes change of instantaneous value of signal frequency/phase. "Pushing" this ever-rotating vector forward is adding phase so temporary increment of frequency. "Holding" it back works otherwise. It is easy to observe with typical generator when FM signal at low carrier frequency has huge deviation - modulated signal "stops" for a moment at some DC value, when carrier frequency and "holding" back are equal for that moment. What is your opinion of such interpretation of I-Q plane? I am just playing smart ;) and you are the boss in practice. I haven't seen better explanation of I-Q plane on YT. Thank you for sharing your great videos!
The carrier comes from the quadrature LOs (local oscillators). When the I and Q values are DC, that means that the two LO amplitudes are constant, so when they are added up, you get an unmodulated CW carrier at the LO frequency. When the IQ vector rotates, you *move* the carrier frequency from the LO frequency - either up or down (depending on direction of rotation) by an amount equal to the rotational frequency.
In the video, the resultant of quadrature signals ( Sin and Cos waves having equal frequency and magnitude) is shown as a diagonal line at 45 degrees to the X-axis when plotted on paper and drawn on the Oscilloscope. I presume that plots/drawings are not done considering Sin values on X-Axis and Cos values on Y-Axis (as in the case of Lissajous figures) otherwise the plot/drawing would be a circle. Is there any other mode on the Oscilloscope for drawing phasors in a vectorial form?
Thanks for this great videos. I liked these IQ signal videos and the PLL one. I just have a question, Lets say I have this one hz frequency offset. Is it possible to convert that vector rotation to a DC value that corresponds to my frequency offset? What is the simplest way to do it? either by circuit or by simulink block. thanks again
As shown in the PLL video, a phase/frequency detector can be used to give a DC output (when filtered) that is proportional to the phase or frequency difference.
In the 40's and 50's they didn't have frequency counters so they used Lissajous patterns as a frequency counter but i don't know how to use lissajous patterns as a frequency counter. Try to make a video lesson on how to show using the Oscilloscope Lissajous Patterns as a Frequency Counter because you have to counter the number of LOBES.
If they aren't locked, then it would be virtually impossible to make the two signals identical in frequency and control the phase. In other words, the resulting phasor will always rotate one way or the other.
It would have hit home even harder for me if you would have shown each signal on a multi trace scope so I could see the actual waveforms used to make the result.
Hey Alan, why is it that the phase jump in PSK or QAM does not cause any problems with unwanted frequency components in the spectrum? To me it always looks like the phase jumps must create all sorts of higher frequency components. Are they just all filtered out or what? Could be an interesting measurement with the MDO.
Yes, if the phase is changed very quickly, then it makes the occupied bandwidth wider. In most cases, the baseband (IQ) signals are filtered to restrict the bandwidth of the modulated signal.
Seems as though you could make an analog clock that appears on your scope screen. Not sure if you could include all three angles needed ie hour, minutes, and second hands. Just a comical thought.
SSB via phasing method is as contemporary as it gets in SSB radios. The 90 degree phase shift over the entire audio passband is done in software via Hilbert transform. One can approximate a Hilbert transformer via FIR filter. Interesting stuff to play with.
I first remember hearing about phasing SSB rigs from the old Central Electronics 100V from the late 1950s. Lots easier to do today with the Hilbert transform filter in DSP.
cny02253 Yes, absolutely. I had a friend (now silent key) that worked with those guys and was responsible for the broadband tuning circuit that was also used in those rigs.
Thanks for the video. As the combined phase shifts one way or another, what is the zero reference? The video said something about the clocks being linked at the sources, but is the output scope also clocked?
The scope is shown using XY mode - so it is just displaying the two inputs with respect to each other - one driving the vertical position and the other driving the horizontal position of the beam.
+w2aew this video shows that the two sinewaves influence the vector shown on the oscilloscope, in school I learned that putting in multiple sinewaves at different frequencies will cause it to act like a block-pulse. We needed that given to come up with a way to calculate the THD ratio for the block-pulse, but I was curious as to how it would look like
I know how to make an oscillator to generate a sin signal with discrete transistors and( i don't know what is the little white cube that you use in your video because i searched on our local market i didn't found those mixers) if possible Can you make a video tutor to design a mixer and Quadrature signals (Sin and Cos) oscillator using easy to find components like regular transistors , IFT or capacitors.Thanks.
There are some good write-ups on this by Marki Microwave: www.markimicrowave.com/blog/top-7-ways-to-create-a-quadrature-90-phase-shift/ www.markimicrowave.com/assets/appnotes/IQ_IR_SSB_Mixer_Primer.pdf
The concept of I,Q modulator is explained in great detail in: ruclips.net/video/h_7d-m1ehoY/видео.html #170: Basics of IQ Signals and IQ modulation & demodulation - A tutorial
Yes, you are right. I caught that mistake earlier, and if you watch the video on a PC, you'll see a screen annotation that pops up to help correct my error in speaking. Thank you for paying attention!
Actually, I have annotations turned off, that's why I didn't see your correction. :) I love your videos anyway. And I'd love to see some detailed explanation of this QI demodulation, maybe even with some math, which would show how those Q and I are actually being extracted from the received RF signal using multipliers. Thank you for your very entertaining and highly educational work!
...Oh! theres more, strangely enough this instruction will also help resolve some firmware issues Im having. Sir, I will subscribe, this is a good day. -By the way, did the renowned RF/A/MS circuit simulation guru Kenneth Kundert once work at Tektronix?
Thanks for the info, yes he worked at Keysight (formerly Agilent) as he worked on the harmonic balance engine for RF circuit simulation. ...Then a few years later worked on a similar remit in developing the Flexible balance algorithm for the SpectreRF circuit simulator in Cadence.
Sorry, how do you get the picture on 4:24? If i send sine to channel X, and cosine to channel Y, i am obviously getting a circle, like here: dood.al/oscilloscope/#0.0,0.0,0,0,0,0,0.0,2,1,sin(2*PI*a*t),cos(2*PI*a*t),3,1,0,1,302,0,0,0. What is the connection schema? Thanks!
I figured out how to recreate it: dood.al/oscilloscope/#0,0,0,0,0,0,0.01,4,1,a*cos(2*PI+t),b*cos(2*PI+t),0,0.0,0,0.76,125,0,0,0 I don't understand how his scope is showing this though because that would mean that both waves are in-phase, which obviously they aren't.
Why doesn't the phasor rotate all the time, with no modulation? When there's no modulation, you're just adding sine and cosine functions - shouldn't that cause constant rotation?
The I and Q represent the peak amplitude of the sine and cosine waves, not the instantaneous voltage. So, a constant I and a constant Q represents a continuous, unchanging, constant frequency tone at the frequency of the I and Q functions.
@@w2aew I think I get it now, thanks...so both I and Q are modulated with the same AM envelope, and the scope is showing how much of that envelope each one is carrying. So the X and Y inputs have the same phase (because there's only one AM signal) and the angle depends on the difference in peak amplitude between I and Q - is that right?
hello, ive been watching and enjoy your videos and was wondering if you could help me out. i dont know if youve heard about a space game called elite dangerous, but its fantastic. there is currently a spectrogram image projected by an object in the game that 10s of thousands of people have been trying to solve for over a month now. i believe the image has something to do with IQ modulations of waveforms. im an auto technician and dont get a lot of time with this area. i will post a link to the image.
Not familiar with the game. I looked at the image and I'm not sure it has to do with IQ modulation. Maybe a good perspective is to recognize that the colors in the spectrogram refer to amplitude (like a z-axis), so possibly visualizing the figure in 3D, and somehow using the four smaller figures surrounding the circular element as some kind of registration or rotation references... That's all I got...
Heh, well I appreciate the response. There are many theories and several leads, but this was the one I was kind of going with. If you don't see the relation though, I'm sure there is none.
This is so incredibly cool. This stuff is becoming a lost art. I got an EE degree in the early 80's but in my career I worked on the physics of solid state devices, so never used and quickly forgot the type of stuff your videos are about. I am eager now in retirement to go back and relearn this stuff I consider to be "classic" electrical engineering. Today so much is digital work driven by huge simulation programs that few really know this lost art. I am drooling over your scopes and test equipment. Thanks for the wonderful videos.
I'm an analog guy at heart, so my videos focus mainly on these topics. And, since I work for Tektronix, I have great access to wonderful equipment, which really helps in the videos.
Ditto what Paul said above, I too am enjoying a late in life re-enlightenment :) Thanks for the great videos.
Far from a lost art, SDR radios using IQ modulation and demodulation are proliferating. Real world use is driving increasing interest. I'm a licensed amateur radio operator and I now have several SDR receivers, two SDR transceivers and my analog transceiver has an IF tap for I/Q demodulation to monitor a wide swath of a band.
Me too, at 51. Maybe it comes with the age 🙂
I concur with your point. My career mainly involved ABB Distributive Control Systems with 4-20 mA I/P valve controllers (current to Pneumatic) and Rosemount transmitters. After so many years of that, my understanding of the subject of many of these videos has atrophied completely. It's nice in retirement to get back to communication electronics. By the way Paul, I've enjoyed your videos very much, especially the two Arduino courses and the Learn Fusion 360 or die trying!!! God Bless my friend.
Truly an eye-opening material. The answer to the question "how does a transmitter alter frequency?" is "it doesn't, it controls the amplitude"
Amazing you are such a great teacher. Never heard before a more comprehensive an illustrative explanation like this
OMG, You don't how much I wish my undergraduate courses would have been this clear!
These videos are a great example of why schools are now obsolete.
I'm sat here wondering why you're not my comms lecturer, or why I'm not taught like this at university. Simple topics are overly complicated for students for some reason. I've learnt and understood so much in 15 minutes compared to hours of lectures
Maybe you should share this video with your professor!
The problem is really that these people fall into an annual syllabus and come up with a standard set of teaching materials. If you understand it at first pass great, you are the lucky one. The difference here is clear, if you love the subject you'll generally be a great teacher. Far too many teachers just don't love it, it's a day job
True in university we only learn complicated formulas and nothing else !
The real problem is that in most Universities there are very few good "teachers"! Probably 70% of the Lecturers/Professors are first and foremost "researchers". They devote the majority of their time to publishing papers to get grants (and by that to also advance their careers). When you can find a good researcher who is a great teacher too, you've struck gold!
Yeah, I guess the concept that is missed in universities is "abstraction level"... Before digging into mathematical treatment one should first show what those things even are! After all, all that knowledge actually emerged from these natural, organic concepts and relationships.
why were you not my professor, I can understand you, you make sense and "speak" English not sure what my professor spoke, His native tong was confusing language. I am just too overjoyed at your videos, what a mental relief to finally understand stuff . You're a Ham . Communications guys we have a Power company were I work, and my professor at college could use a lesson from you. You really know how to teach. Forever grateful to you deep kindness. You use great tools like your scopes and mixers to put it all together, a visual picture is worth millions.
best 73s Mike wb7qxu
I feel like you should be accredited and I should be able to gain credits toward a Bachelor of Science degree having watched only a few of your videos! I wish you were running our labs at DeVry in Woodbridge NJ back in the late 80's! :) .... but seriously this is how every engineering classroom should be taught! Hand's on in the lab side by side with the theory!
there's a trend here of old 80s guys re-learning what they forgot (I'm one). I worry about kids of today and I am hopeful that SDR may play some role in re-igniting interest because a computer is involved and kids love them
I came here expecting a modulation demo. Took me a while to realise that you were demonstrating AM and FM demodulation setups, because I foolishly hurried pass the important details in the intro. Had to re-watch it over a few times to pickup my mistake, now the vector traces on the scope all make sense! Thanks so much for all the effort you put into these tutorials.
The phasor diagram, especially as you displayed on your scope, visually ties it all together for me. Great job as always! A video on the math used in designing the double ring mixer would be very informative.
Excellent lecture, 40 year old memories reinforced!
I found these tutorials after trying to understand what the I/Q inputs and outputs on a K3 radio were all about. Thanks for a very easy to understand presentation. This also helps me to wrap my brain around the analog world of voltage and current relationships in a L/C circuit and Antennas!
By far the best lectures over the entire channel!! Wish that my teacher was at least half as good as you are when he tried explaining quadratures 35yrs ago! - Fortunately the books were better. (No internet that time.)
Very clear communication skills, perfect and simple demonstrations, excellent job! Thanks for sharing and spending your time making these videos!! - This is what internet is all about. 👍👌
Awesome video! We just did a project in school, in a signal processing course, where we sent a digital message over an audio channel, using OFDM and QPSK. It is an interesting subject, thank you for sharing your knowledge!
This channel is a gem! Thankyou w2aew
Your short 'Lab' lessons (theory and practice) really inspire me (every time) to go and to build it myself right away 🙂...and to learn more on the subject. Thanks for that 👍
Thank you for making such a great, absolutely amazing, a documentary video about IQ signals. If anyone asks what the heck is i and q, this video (1-2) answers it totally.
Wow! A few years ago, I took a communications course that covered this material... I was able to get through all the mathematics, but I never quite "got it". Seeing your examples displayed on the scope really made it all click for me. Thanks!
All smiles over here: I've learned a lot. Glad I noticed part 2. Thanks for the time and effort.
Hi, Alan. :-)
Always great to watch you videos for they are accurate, polite, and easy.
Thank you.
PS. I have an idea to design a sort of "direct conversion superhet": 45MHz 1st IF (I have a pair of 4520D crystal filters) then a simple LC or RC phase shifting network and an IQ product detector.
It looks like your diagram for SSB generation, but IF input instead of Audio input.
Yes, I'm trying to avoid building a polyphase network for I have no proper parts for that. :-)
I can control it with a single si5351a (one channel for 45.1MHz...75MHz VFO and two channels for 45MHz quadrature BFO).
Advantages: no mirror image while no polyphase network, no parasitic radiation, no BPFs - just 30MHz LPF, not much of relays and switches, microcontroller (I have STM32F103, STM32F303 and ESP32) can be used as DSP to code digital AF filters.
Disadvantages: a noisy MC and si5351, high IF, high current consumption, need in 12V power supply (for I have no low voltage parts for 45MHz).
What do you say? :-)
@7:30 ahhhhhhh ok so this is showing the two components of a complex exponential function e^jwt where the rate of spinning is w. great explanation.
Thanks for another excellent video!
Showing how these things work on a scope, makes it all much better to understand.
Fantastic video... I'm in the same boat as Paul and Andy below, and am really enjoying these. Thank you so much.
So basically it will represent nicely Lissajous curves if you mix AM with FM modulation in different ratio for a continuous signals and dots for a discreet signals. Nice explanation.
Thank you sir! I'm back. I'm not really sure why but I was interrupted for a week or two. Powering through the the videos one by one! Thank you!
Very nice demonstration. Looking forward for future parts explaining frequency domain correlation with used modulation. Deviation, modulation index, gaussian FSK shaping, spectral efficiency etc. GJ!
Great clip again:
In Injection locking two oscillators , at the same frequency, are used to create oscillation with much lower phase noise.
I guess we can use your method ( IQ FM de-modulator with an X-Y oscilloscope) for checking how good the two oscillator are locked.
Nothing like analog signals to state a concept. Great job.
Excellent tutorial as always! Now it's all clear for me about IQ method for FM/AM modulation. Please keep it going. I'd like to see more SDR related tutorials from you. Could you provide me an information where I can find more useful materials about SDR?
Thanks for taking the time to make these videos. You do an excellent job of visually explaining these concepts. Keep up the good work! I'm learning a lot from you.
Great video ! As I did not remember how it works, your video reminds me how it does ! Thank you very much !
Yet another awesome video. Very clear explanations... And the visualisation makes the concepts even easier to understand. Thank you!
Roger.
VE3RDE
Once again - brilliant. Thank you very much! Love it!
I'm just at a lost why anyone can give this a thumbs down. Do you know if the devil watches youtube? I thought he was too busy playing foosball.
You are God send! I was struggling to understand it...thank you so much Sir!
You are the very definition of an Elmer. Thank you for posting.
Thank you for this, parts 1 and 2 on I-Q signals. I never understood it before, but feel I have at least a handle on this now.
I wish I could like this twice!
Great explanation thank you! I missed this video before.
You sir are a true scholar, keep up the good work!
On a related note to FM, could you identify how incidental FM creates unbalanced sidebands on an AM signal?
chris kaplan Hmm - I never looked at that. I would suspect that it would be caused by a phase inversion of the lower sidebands on FM, partially cancelling the AM LSB. Certainly worth looking at...
Wow you really have a piece of hardware there!! Im a teacher and trying to explain these with ol'n faithful 1496 is a pain in the...
Like everyone else here I very much appreciate your videos, they're brilliant thank you!
Have you done a video explaining how a receiver locks its frequency/phase reference to the intended phase of the incoming signal? I struggle to understand how the receiver knows what is considered 0 phase shift for it to then determine deviations from that??
In this video you phase lock the sig gens together but how do remote receivers achieve this?
Thanks again, I'm very grateful for your work.
Most commonly this is done by using a specific "sync pattern" in the data transmission - the rx looks for this sync pattern at the various phase rotations, then will use the phase rotation that properly decodes the sync word.
@@w2aew Ah I see! And is the sync pattern then broadcast periodically to keep everything aligned and prevent drift?
Amazing, thank you. That was one of the last pieces of the puzzle I needed to grasp concept of IQ modulation - since essentially, they are all exactly the same sinusoids if you have nothing to reference them against right!?
Much obliged to you, Thanks again for the videos.
The phasor visualization on oscilloscope is really cool
I know the new QCX transcievers use IQ for it's mod/demod so was interested in learning more. As always excellent theorotical examples but some practical examples would be very helpful. For instance in the past two videos you talk about input and the resulting outputs (either direction) but not how to use those in a radio to actually transmit or receive something. Reminds me of my first physics classes. We learned all this theory and I thought yeah so what? In later years we actually did practical experiments to show the concepts in physics and I thought "Eureka" that's what it's all about!
You should make a video explaining the mixer and signal generator setup. That would help us to know, how to interface signal generators and mixer chip sets
It's going to take a few replays for this to sink into my old brain. But I do remember the phase method of SSB generation. The HealthKit Apache transmitter SSB adapter used phasing to produce the single sideband from the AM signal.
Part 3, part 3!!! :D
I too would like to do this experiment at the lab. Could you Please tell me where I can get those multipliers and signals splitters from? Your video actually persuaded me to try this on my own! you are truly an inspiring person.
The multipliers are simply ADE-1ASK mixers from Mini-Circuits. The splitter is a junkbox resistive splitter. You can also get an appropriate resistive RF splitter from Mini-Circuits.
Thank you so much. And thanks a lot for this great videos on IQ. its my second day going through them and trying to understand them. Each time, I learn something new.
Very cool thank you so much. But I was looking forward to and you skip over how to Demodulate the FM signal.
Incredible level of teaching. AMAZING !. Can you please direct me to some good material for C4FM modulation ?
great, the only thing I miss is a block diagram for AM and FM simular to the one you give for the SSB phasing method
another great tutorial.... :)
Great video Alan, thanks.
5:00 Amplitude is just a factor of the radius. A phase is a delay or the opposite of "going around" like the first circle (the circumference.) I guess we can have 2 phases. 1 in the x and one in the y calculation. Maybe 3D applies sometimes. I'm just speaking from geometry and not sure how far the "phase" goes for the names on things.
Amplitude is the length of the "ray" from the origin, phase is the angle of the ray with respect to the horizontal axis.
I would like to know how to build the 90 deg shift network.
Welcome back onboard sir!
at 13:32 what is the name of the component/suggested method for adding or substracting the quadrature signal for usb/lsb selection?
Amazing video! I was wondering, is there a different method for working with frequency modulation, i.e. FSK (besides segmenting the constellation diagram as with PSK), because I imagine it would be difficult to determine the "rate of rotation" of your phasor vector in order to determine the frequency at a particular time. Might there be some Fourier transforms involved?
Very nice. I guess you can use this to double the frequency or can other methods be used for that?
EXCELLENT Video, thank you, any chance to give more details on the mixers? what they are and how we can make one at home? possible?
The mixers used here are simply the classic diode ring mixers. These are MiniCircuits ADE-1ASK, only because that's what I had on hand. You can build them yourself as shown in this video:
How a Diode Ring Mixer works | Mixer operation theory and measurement
Very nice. Just some questions. How does the reciever know the absolute phase and amplitude of the transmitter? Is the information encoded in absolute phase or in differential phase shift? How does the LO of the Reciever "lock in" on the base frequency and of the transmitter's LO or doesn't it need to?
I mean, I only have one antenna and if I flip it upside down my phase shifts 180.
I mean I have to cross correlate to a second input or encode/decode in the phase differential of the frequeny,right?
The receiver doesn't know the absolute phase. So, typically one of two things are done. Data is encoded differentially as you suggested, or (more commonly) the data contains a specific sync sequence that is properly decoded only at one of the possible phase rotations. The receiver demodulates the data, looking for this sync sequence to establish the reference phase, then decodes the rest of the transmission using this phase reference. Often, there is a small frequency offset too, so the receiver will also compensate for that too (de-rotating the vector).
Thank you. I did not know that. I know the basic math of it but not the real world implementation.
Can you do a video on how the synchronisation works? And on QAM.How does the QAM reciever know how to scale the amplitude? Why is the QAM diagram square and not circular?
Also,I find your videos informative and well made. What I especially remember is learning about how diodes can be RF switches and how the diode ring mixer is just an assembly of switches.
I did not know diode mixers operate in non linear mode,making them square wave sensitive.
QAM constellations are usually square because the I and Q signals are typically matched in amplitude to make it easier to null the Carrier feedthru (null DC offset).
*****
....what did he say?
Nice video on explaining FM using phasor method. As one more step further, how to explain the nulling of carrier in FM modulation for a certain FM deviation and modulation frequency using the phasor method? I know the Bessel function can describe it, is there an intuitive way to explain it using the phasor method?
Probably the most obvious thing is that the average I and Q values over time would be equal to zero when there is a carrier null.
great video!
How long did it take you to produce that video? There is so much information at any given point, it is really well structured. Setting up those demos, drawing diagrams and later edit/cut all the footage... I bet it would take me 3 days to shoot that video, even if I had all the instruments and tools!
This one took the better part of 3 hours. You're right, some of them take days to do, including setup, drawings, building, testing, shooting and editing.
Спасибо огромное!
It's so logical.
I love your presentations and I am really thankful for what you shared.
Angle increment is uniform in AM so the phase is actually constantly incrementing. This is what makes unmodulated carrier. Am I right? :)
Continuously rotating phase indicates an off-center carrier. AM is the modulation of the length of the vector formed by the IQ components. If they don't rotate, that means the carrier is at the center frequency.
For a vector with constant amplitude and no phase (angle) increment the I and Q would be constant and therefore just make a DC signal. The vector must rotate at constant angular velocity to create carrier. Therefore phase increments. Or do you assume here that IQ plane rotates while vector may stay in place as some authors do?
In 6:26 it should be said that how fast this vector spins around equals to signal (carrier) frequency. Change in speed of spinning makes change of instantaneous value of signal frequency/phase. "Pushing" this ever-rotating vector forward is adding phase so temporary increment of frequency. "Holding" it back works otherwise. It is easy to observe with typical generator when FM signal at low carrier frequency has huge deviation - modulated signal "stops" for a moment at some DC value, when carrier frequency and "holding" back are equal for that moment. What is your opinion of such interpretation of I-Q plane?
I am just playing smart ;) and you are the boss in practice. I haven't seen better explanation of I-Q plane on YT. Thank you for sharing your great videos!
The carrier comes from the quadrature LOs (local oscillators). When the I and Q values are DC, that means that the two LO amplitudes are constant, so when they are added up, you get an unmodulated CW carrier at the LO frequency. When the IQ vector rotates, you *move* the carrier frequency from the LO frequency - either up or down (depending on direction of rotation) by an amount equal to the rotational frequency.
In the video, the resultant of quadrature signals ( Sin and Cos waves having equal frequency and magnitude) is shown as a diagonal line at 45 degrees to the X-axis when plotted on paper and drawn on the Oscilloscope. I presume that plots/drawings are not done considering Sin values on X-Axis and Cos values on Y-Axis (as in the case of Lissajous figures) otherwise the plot/drawing would be a circle. Is there any other mode on the Oscilloscope for drawing phasors in a vectorial form?
Thanks for this great videos. I liked these IQ signal videos and the PLL one. I just have a question, Lets say I have this one hz frequency offset. Is it possible to convert that vector rotation to a DC value that corresponds to my frequency offset? What is the simplest way to do it? either by circuit or by simulink block.
thanks again
As shown in the PLL video, a phase/frequency detector can be used to give a DC output (when filtered) that is proportional to the phase or frequency difference.
great videos man..
In the 40's and 50's they didn't have frequency counters so they used Lissajous patterns as a frequency counter but i don't know how to use lissajous patterns as a frequency counter. Try to make a video lesson on how to show using the Oscilloscope Lissajous Patterns as a Frequency Counter because you have to counter the number of LOBES.
Yes, search my channel and you will find a video on Lissajous Patterns.
@@w2aew I did but it doesn't teach how to use Lissajous patterns as a frequency counter by counting the number of lobes and convert it to a frequency
In SSB generation, it should be '-' for USB and '+' for LSB.
Could you please explain as to why the two signal generators have to be phase locked? If they were not phase locked, what would happen? Thanks a lot.
If they aren't locked, then it would be virtually impossible to make the two signals identical in frequency and control the phase. In other words, the resulting phasor will always rotate one way or the other.
hey, thanks so much!
I wonder how you made the two generators phase locked ? I did'nt saw a connection between the generators.
I used a two-channel function generator - both channels are inherently locked because the operate from the same reference.
Sorry, I thought that I have seen two generators.. Very stupid. Sincerly yours
super good !!!
It would have hit home even harder for me if you would have shown each signal on a multi trace scope so I could see the actual waveforms used to make the result.
Hey Alan, why is it that the phase jump in PSK or QAM does not cause any problems with unwanted frequency components in the spectrum? To me it always looks like the phase jumps must create all sorts of higher frequency components. Are they just all filtered out or what? Could be an interesting measurement with the MDO.
Yes, if the phase is changed very quickly, then it makes the occupied bandwidth wider. In most cases, the baseband (IQ) signals are filtered to restrict the bandwidth of the modulated signal.
You'll often see phase changes happen at zero crossing points to minimize high frequency discontinuities.
Seems as though you could make an analog clock that appears on your scope screen. Not sure if you could include all three angles needed ie hour, minutes, and second hands. Just a comical thought.
SSB via phasing method is as contemporary as it gets in SSB radios. The 90 degree phase shift over the entire audio passband is done in software via Hilbert transform. One can approximate a Hilbert transformer via FIR filter. Interesting stuff to play with.
I first remember hearing about phasing SSB rigs from the old Central Electronics 100V from the late 1950s. Lots easier to do today with the Hilbert transform filter in DSP.
***** Credit Wes Schum and Joe Batchelor for the CE 100v and 200BV. Two brilliant men, and the true fathers of SSB.
cny02253 Yes, absolutely. I had a friend (now silent key) that worked with those guys and was responsible for the broadband tuning circuit that was also used in those rigs.
Thanks for the video. As the combined phase shifts one way or another, what is the zero reference? The video said something about the clocks being linked at the sources, but is the output scope also clocked?
The scope is shown using XY mode - so it is just displaying the two inputs with respect to each other - one driving the vertical position and the other driving the horizontal position of the beam.
@@w2aew OK, thanks. In an actual non-lab signal processing situation, would the two signals need to be clocked somehow?
great video as always :)
this is really great, but is there a way to show this as a deformed sine wave that has the same look as a block-pulse?
+Common Freak I'm not sure what you're asking for...
+w2aew this video shows that the two sinewaves influence the vector shown on the oscilloscope, in school I learned that putting in multiple sinewaves at different frequencies will cause it to act like a block-pulse. We needed that given to come up with a way to calculate the THD ratio for the block-pulse, but I was curious as to how it would look like
+Common Freak With square waves input, the basic shape in XY will be square instead of circular.
I know how to make an oscillator to generate a sin signal with discrete transistors and( i don't know what is the little white cube that you use in your video because i searched on our local market i didn't found those mixers) if possible Can you make a video tutor to design a mixer and Quadrature signals (Sin and Cos) oscillator using easy to find components like regular transistors , IFT or capacitors.Thanks.
There are some good write-ups on this by Marki Microwave:
www.markimicrowave.com/blog/top-7-ways-to-create-a-quadrature-90-phase-shift/
www.markimicrowave.com/assets/appnotes/IQ_IR_SSB_Mixer_Primer.pdf
Why do we need I and Q signal?
Why we need to generate I n q in modulator
Any problem if we will not use I Q signal?
The concept of I,Q modulator is explained in great detail in:
ruclips.net/video/h_7d-m1ehoY/видео.html
#170: Basics of IQ Signals and IQ modulation & demodulation - A tutorial
Excellent....
👍👍👍
at 5:32 you probably meant to say "frequency difference" instead of "phase difference"
Yes, you are right. I caught that mistake earlier, and if you watch the video on a PC, you'll see a screen annotation that pops up to help correct my error in speaking. Thank you for paying attention!
Actually, I have annotations turned off, that's why I didn't see your correction. :) I love your videos anyway. And I'd love to see some detailed explanation of this QI demodulation, maybe even with some math, which would show how those Q and I are actually being extracted from the received RF signal using multipliers. Thank you for your very entertaining and highly educational work!
Thank you!
Is there a ham publication with experiments like these demos?
With all the receivers we routinely carry around, it should be possible to simulate some of the more advanced equipment with things at hand!
...Oh! theres more, strangely enough this instruction will also help resolve some firmware issues Im having. Sir, I will subscribe, this is a good day. -By the way, did the renowned RF/A/MS circuit simulation guru Kenneth Kundert once work at Tektronix?
I believe he worked for HP at one time (prior to Agilent/Keysight)
Thanks for the info, yes he worked at Keysight (formerly Agilent) as he worked on the harmonic balance engine for RF circuit simulation. ...Then a few years later worked on a similar remit in developing the Flexible balance algorithm for the SpectreRF circuit simulator in Cadence.
Really cool!
I am struggling how ofdm is generated using iq modulation.
Why we don't use just sample of RF Signal without I and Q component? As i understood we use IQ component to only analyze the Signal. Am i right?
In some cases, you can use simple time-domain samples. IQ is often used when understanding the phase of the signal is needed.
THX THX THX!!! This I never fully understand :))) t.up!
Sorry, how do you get the picture on 4:24? If i send sine to channel X, and cosine to channel Y, i am obviously getting a circle, like here:
dood.al/oscilloscope/#0.0,0.0,0,0,0,0,0.0,2,1,sin(2*PI*a*t),cos(2*PI*a*t),3,1,0,1,302,0,0,0.
What is the connection schema?
Thanks!
I figured out how to recreate it: dood.al/oscilloscope/#0,0,0,0,0,0,0.01,4,1,a*cos(2*PI+t),b*cos(2*PI+t),0,0.0,0,0.76,125,0,0,0
I don't understand how his scope is showing this though because that would mean that both waves are in-phase, which obviously they aren't.
Wow
On demodulation it is not obvious to me how an incoming RF single would be broken down into I and Q signals.
Splitting the RF signal into two mixers, each fed with an LO (at the RF frequency) which are offset by 90 degrees, will result in I and Q outputs.
Would you please make a video of QPSK...please
Have you seen this video? QPSK is shown and discussed beginning about 13 minutes in.
ruclips.net/video/h_7d-m1ehoY/видео.html
How to synchronize tx and rx LO's?
You typically don't - receivers will generally have a way to account for LO offset.
@@w2aew so the way is a black box))
Why doesn't the phasor rotate all the time, with no modulation? When there's no modulation, you're just adding sine and cosine functions - shouldn't that cause constant rotation?
The I and Q represent the peak amplitude of the sine and cosine waves, not the instantaneous voltage. So, a constant I and a constant Q represents a continuous, unchanging, constant frequency tone at the frequency of the I and Q functions.
@w2aew I thought the scope in XY mode showed the instantaneous voltages of I and Q?
@@johnbyrne1022 In this case, the XY mode is plotting the varying sinusoids, not just the magnitude of I and Q.
@@w2aew I think I get it now, thanks...so both I and Q are modulated with the same AM envelope, and the scope is showing how much of that envelope each one is carrying. So the X and Y inputs have the same phase (because there's only one AM signal) and the angle depends on the difference in peak amplitude between I and Q - is that right?
would you plese describe 16 and 32 QPSK
I assume that you really mean 16QAM and 32QAM. There is no such thing as 16 QPSK...
👍
hello, ive been watching and enjoy your videos and was wondering if you could help me out. i dont know if youve heard about a space game called elite dangerous, but its fantastic. there is currently a spectrogram image projected by an object in the game that 10s of thousands of people have been trying to solve for over a month now. i believe the image has something to do with IQ modulations of waveforms. im an auto technician and dont get a lot of time with this area. i will post a link to the image.
i.imgur.com/t7qvIN2.jpg
there may be some missing info, the central part is the important part. id just like observations or analysis if you can.
Not familiar with the game. I looked at the image and I'm not sure it has to do with IQ modulation. Maybe a good perspective is to recognize that the colors in the spectrogram refer to amplitude (like a z-axis), so possibly visualizing the figure in 3D, and somehow using the four smaller figures surrounding the circular element as some kind of registration or rotation references... That's all I got...
Heh, well I appreciate the response. There are many theories and several leads, but this was the one I was kind of going with. If you don't see the relation though, I'm sure there is none.