| ▲ | Two Birds with One Tone: I/Q Signals and Fourier Transform(wirelesspi.com) |
| 104 points by teleforce 4 days ago | 28 comments |
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| ▲ | KeplerBoy 4 days ago | parent | next [-] |
| The liberal use of AI generated images really cheapens the entire article. Please don't do it. At that point I suspect most of the text is also AI generated. |
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| ▲ | dsp_man 3 days ago | parent [-] | | Only two images are AI generated where horses as carriers needed to be shown. Can you please explain why this is a problem? Thank you (Also, all text is written by me :) | | |
| ▲ | CamperBob2 3 days ago | parent | next [-] | | Safe to say that 150 years ago, his great-great-grandpa was ranting about photography putting painters out of work. | |
| ▲ | KeplerBoy 3 days ago | parent | prev [-] | | I guess I just don't like the style of the images, they just scream "AI slop ahead!". Also I don't think they add anything of value to your article, which is indeed well written. So kudos from someone working on radar signal processing! |
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| ▲ | MrBuddyCasino 4 days ago | parent | prev | next [-] |
| This reads like someone proficient in signal processing is explaining the core concepts to another person who is already proficient in signal processing. |
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| ▲ | sevensor 3 days ago | parent | next [-] | | Exactly right! As somebody who’s spent a great deal of time with the discrete Fourier transform, I thought, “this article reads like it was written specifically for me.” I/Q modulation is new to me though. | |
| ▲ | 4 days ago | parent | prev [-] | | [deleted] |
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| ▲ | yodon 4 days ago | parent | prev | next [-] |
| Pro tip: If you're writing an article on the significance of something called I/Q, it's cool to somewhere in the first couple pages say something about what I/Q is. |
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| ▲ | gsf_emergency_2 4 days ago | parent | next [-] | | Q=Quadrature, I=In-phase (As you point out not in the first couple pages, but waaay down) he "explains" those https://wirelesspi.com/two-birds-with-one-tone-i-q-signals-a... Not trying to be charitable like furgot ... The wikipedia page is the first time I've seen authors go pro on the topic | |
| ▲ | wucke13 4 days ago | parent | prev | next [-] | | https://www.pe0sat.vgnet.nl/sdr/iq-data-explained/ This is an excellent introduction to the concept and also to the why complex numbers are used to represent signal samples. | | |
| ▲ | msravi 4 days ago | parent [-] | | I prefer a more "physical" explanation - you have two carriers: sin(wt) and cos(wt), and you're modulating bits I and Q onto the two carriers and adding them up before transmitting. Now, mathematically, that's the same as representing the two bits as I+jQ and multiplying it with cos(wt)+jsin(wt). Demodulation is simply multiplying that output with the complex conjugate cos(wt)-jsin(wt), which in physical terms translates to mixing with a local oscillator output and low pass filtering. | | |
| ▲ | exe34 4 days ago | parent [-] | | Why would you want two carriers? | | |
| ▲ | Sesse__ 4 days ago | parent [-] | | Twice as much information. My go-to for I/Q is: Having two allows you to represent negative frequencies. With a normal, real signal, this is of course impossible (negative frequencies will automatically mirror the positive ones), but if you have a signal centered around e.g. 1 MHz, there's room for above-1MHz and below-1MHz to be meaningfully different. And _that_ allows you to get a complex signal (I/Q), once you pull the center down to 0 Hz for convenience of calculation. |
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| ▲ | dsp_man 3 days ago | parent | prev | next [-] | | Thank you for the suggestion. That's the point. I/Q introduced early gets too complicated. This foundation needs to be built up. | |
| ▲ | ykonstant 4 days ago | parent | prev | next [-] | | Only people with a low I/Q would misunderstand this notation! | |
| ▲ | furgot 4 days ago | parent | prev [-] | | Most technical writing is going to assume some familiarity with the discipline. If a reader encounters unfamiliar vocabulary in a technical article, they'd be well advised to look it up. https://en.wikipedia.org/wiki/In-phase_and_quadrature_compon... |
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| ▲ | mikewarot 4 days ago | parent | prev | next [-] |
| Yikes - why even mention the E and B fields? They aren't relevant to the rest of the article. A few hours playing with Sine and Cosine generators in GNU radio can take you from book knowledge of I/Q complex signals into fully grokking it. You don't even need a radio, just your existing audio I/O. |
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| ▲ | dsp_man 3 days ago | parent | next [-] | | I mentioned E and B fields so that the reader knows why we focus exclusively on sinusoids. Plus, linking the sinusoid to something we see in physics makes it more real. | |
| ▲ | ygritte 3 days ago | parent | prev [-] | | > existing audio I/O I never knew there even is such a thing. Where can I find it? | | |
| ▲ | galangalalgol 3 days ago | parent [-] | | There is a source block for your mic and or audio in. That was one of the first things I played with to understand sdr. I remember seeing a strong tone on a waterfall plot that I could not hear, thinking it was an articfact, then looking at the frequency and realizing I wouldn't be able to hear it. Turned out it was a crt TV. That kind of dates the story. Fun to be had. | | |
| ▲ | ygritte 3 days ago | parent [-] | | Dang, I just realized that I misread it. I was seeing "I/Q" where it says "I/O". My bad. |
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| ▲ | myahio 4 days ago | parent | prev | next [-] |
| Are there any other high-quality sources for articles about signal processing and its actual application in hardware/software?
I've taken signal processing classes at my college and while I have a good grasp of the theory I struggle with actual use case ideas, beyond implementing a simple fir filter on a stm32. |
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| ▲ | esafak 4 days ago | parent | prev [-] |
| Yet another thing from school I've never used in the software world. By the way, QAM is (still) used in 4G and 5G. |
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| ▲ | pythonguython 4 days ago | parent | next [-] | | Come be a DSP engineer. I take FFTs of IQ data almost every single day | |
| ▲ | cycomanic 4 days ago | parent | prev | next [-] | | Some variation of QAM will always be used in communication. As soon as you deal in with EM-waves, be it physics, engineering or even biomedical stuff you will have to deal with complex numbers, which by extension is dealing with I/Q signals. You probably don't need this for programming a server or a website, but it's indispensable for signal processing. | |
| ▲ | userbinator 4 days ago | parent | prev [-] | | Work on low-level software for communications, especially RF, and you will see plenty of this stuff. | | |
| ▲ | cycomanic 4 days ago | parent [-] | | Not just RF, also optical communications. Really, the only domain left where PAM transmission is used is baseband communication for electronics, and datacom for optics. |
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