Re:Two Birds with One Tone: I/Q Signals and Fourier Transform
by cycomanic on Wednesday July 30, 2025 @05:26AM
(#44732328)
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.
Re:Two Birds with One Tone: I/Q Signals and Fourier Transform
by cycomanic on Wednesday July 30, 2025 @05:29AM
(#44732341)
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.
Re:Two Birds with One Tone: I/Q Signals and Fourier Transform
by yodon on Wednesday July 30, 2025 @12:48AM
(#44730975)
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.
Re:Two Birds with One Tone: I/Q Signals and Fourier Transform
by msravi on Wednesday July 30, 2025 @03:11AM
(#44731594)
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.
Re:Two Birds with One Tone: I/Q Signals and Fourier Transform
by Sesse__ on Wednesday July 30, 2025 @04:57AM
(#44732145)
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.
Re:Two Birds with One Tone: I/Q Signals and Fourier Transform
by furgot on Wednesday July 30, 2025 @01:46AM
(#44731179)
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.
Re:Two Birds with One Tone: I/Q Signals and Fourier Transform
by MrBuddyCasino on Wednesday July 30, 2025 @02:01AM
(#44731244)
This reads like someone proficient in signal processing is explaining the core concepts to another person who is already proficient in signal processing.
Re:Two Birds with One Tone: I/Q Signals and Fourier Transform
by sevensor on Wednesday July 30, 2025 @08:14AM
(#44733182)
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.
Re:Two Birds with One Tone: I/Q Signals and Fourier Transform
by mikewarot on Wednesday July 30, 2025 @03:17AM
(#44731630)
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.
Re:Two Birds with One Tone: I/Q Signals and Fourier Transform
by galangalalgol on Wednesday July 30, 2025 @08:45AM
(#44733510)
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.
Re:Two Birds with One Tone: I/Q Signals and Fourier Transform
by dsp_man on Wednesday July 30, 2025 @12:02PM
(#44735956)
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.
Re:Two Birds with One Tone: I/Q Signals and Fourier Transform
by KeplerBoy on Wednesday July 30, 2025 @04:58AM
(#44732149)
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.
Re:Two Birds with One Tone: I/Q Signals and Fourier Transform
by dsp_man on Wednesday July 30, 2025 @11:58AM
(#44735902)
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 :)
Re:Two Birds with One Tone: I/Q Signals and Fourier Transform
by KeplerBoy on Thursday July 31, 2025 @04:35AM
(#44743628)
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!
Re:Two Birds with One Tone: I/Q Signals and Fourier Transform
by myahio on Wednesday July 30, 2025 @07:28AM
(#44732883)
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.
By the way, QAM is (still) used in 4G and 5G.
This is an excellent introduction to the concept and also to the why complex numbers are used to represent signal samples.
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.
(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
https://en.wikipedia.org/wiki/In-phase_and_quadrature_compon...
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.
I never knew there even is such a thing. Where can I find it?
So kudos from someone working on radar signal processing!
https://www.greatscottgadgets.com/sdr/