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Comment by IshKebab | Hacker News Reader

Coincidentally I was planning to write a blog post about what I/Q are, inspired by this very terrible explanation. I recently started playing around with SDR and went to look up what I & Q are, found this page (it is one of the very few explanations) and got completely confused. My main objections:

1. It's actually a fairly simple concept but this page jumps into pages of formulas and irrelevancies. It is also missing motivation for why I/Q exist. No way is this "for dummies"

2. This: "I'd say the true signal is complex, and the real signal is an incomplete projection of it" is factually incorrect. The signal coming down the antenna is real.

I feel like I could explain it better in 1/4 of the text. Would anyone be interested in that?

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Yes, there's many people who would be interested in another explanation of quadrature sampling and why it is essential in modern communications DSP.

A few that I think are useful or have interesting components are:

* https://pysdr.org/content/sampling.html#quadrature-sampling

* https://visual-dsp.switchb.org/

* Understanding Digital Signal Processing by Richard Lyons

Yeah, it doesn't even explain the image frequency problem in traditional superheterodyne receivers, which I'm sure is pretty fundamental to why I/Q exists. (Loosely speaking, a superheterodyne receiver transforms the input frequency to some fixed intermediate frequency by shifting everything by an adjustable local oscillator frequency. However, there are two different input frequencies that produce the same frequency on the output: one above the local oscillator by the same amount as that intermediate frequency, and one below it by the same amount. Those are basically the positive and negative frequencies the article talks about I/Q data being able to distinguish.)

Sure, if you can do that, why not? I was also searching for a good explanation on I/Q data when I found this. I posted it since I found the page interesting, but also, I did not dive into the details. I'm more interested in the conceptual explanation, and not the hands-on details.

If you could add another (potentially better explanation), that could be beneficial for future learners (not necessarily limited to the HN community).

> Would anyone be interested in that?

I would, as I read this article but I also think a clearer explanation could be made.

See what you think of

https://pysdr.org/content/sampling.html#

first.

It's definitely better, but still super long! And again it dives into complex numbers before motivating anything.

I really just wanted something that just explained what I and Q were and why they existed, without going into what Nyquist and Fourier transforms.

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