Two Birds with One Tone: I/Q Signals and Fourier Transform

https://wirelesspi.com/two-birds-with-one-tone-i-q-signals-and-fourier-transform-part-1/

by teleforce • 12 months ago

105 27 12 months ago

wirelesspi.com

esafak• 12 months ago

Yet another thing from school I've never used in the software world.

By the way, QAM is (still) used in 4G and 5G.

pythonguython• 12 months ago

Come be a DSP engineer. I take FFTs of IQ data almost every single day

userbinator• 12 months ago

Work on low-level software for communications, especially RF, and you will see plenty of this stuff.

cycomanic2• 12 months ago

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.

cycomanic2• 12 months ago

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.

yodon• 12 months ago

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.

furgot• 12 months ago

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...

gsf_emergency_2• 12 months ago

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• 12 months ago

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• 12 months ago

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.

ykonstant• 12 months ago

Only people with a low I/Q would misunderstand this notation!

dsp_man3• 12 months ago

Thank you for the suggestion. That's the point. I/Q introduced early gets too complicated. This foundation needs to be built up.

MrBuddyCasino• 12 months ago

This reads like someone proficient in signal processing is explaining the core concepts to another person who is already proficient in signal processing.

sevensor• 12 months ago

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.

mikewarot• 12 months ago

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.

ygritte2• 12 months ago

existing audio I/O

I never knew there even is such a thing. Where can I find it?

galangalalgol• 12 months ago

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.

dsp_man3• 12 months ago

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.

KeplerBoy2• 12 months ago

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.

dsp_man3• 12 months ago

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• 12 months ago

Safe to say that 150 years ago, his great-great-grandpa was ranting about photography putting painters out of work.

KeplerBoy2• 12 months ago

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!

myahio• 12 months ago

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.

drweevil• 12 months ago

Great Scott Gadgets has an excellent series of videos on the subject.

https://www.greatscottgadgets.com/sdr/

Two Birds with One Tone: I/Q Signals and Fourier Transform

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