REQ: simplified explanation of SDR demodulation

[KN4UJW]

I am relatively new ham - Tech in 2019. I am retired Software Engineer - many years as contractor at Robins AFB.
I am looking for simplified ("6th grade level") description of SDR demodulation. I am not a math person.
Many articles, videos, books, etc I've looked at start throwing up calculus formulas which I don't understand.
Looking for description of what formulas are trying to illustrate. Once I have general understanding of how
time-series points generated by ADC from radio spectrum signal become audio, I might be able to
understand what the equations are trying to say.

Please provide any references (articles, videos, books, etc) you feel may be appropriate.
Thank you.

 

[NebraskaCoder]

This is a very low effort response post from ChatGPT. Maybe it will help you?

For a simplified understanding of SDR (Software-Defined Radio) demodulation, I found several resources that explain the concept without delving into complex mathematics.

1. **Radio-Hobbyist**: They offer a beginner's guide to SDR, focusing on the basics of replacing traditional analog radio components with digital signal processing algorithms. This guide explains how SDR provides a more flexible approach to radio communication, allowing advanced signal processing and modulation techniques that aren't possible with traditional hardware-based approaches [[❞]](https://radio-hobbyist.com/beginners-guide-to-software-defined-radio/).

2. **RTL-SDR.com**: They have a short document by the RSGB (Radio Society of Great Britain) that explains core DSP (Digital Signal Processing) concepts without any math. This includes terms like sampling, nyquist, aliasing, and others, offering a basic understanding of SDR relevant for amateur radio exam tutors and beginners [[❞]](https://www.rtl-sdr.com/short-article-explaining-dsp-basics-without-math/).

3. **DH1TW.de**: This website provides an explanation of the SDR concept from a non-mathematical perspective. It outlines how the baseband signal in SDR is processed/generated in the Signal Processing component, which handles modulation, demodulation, filtering, and noise reduction. The site also explains the physical and logical independence of the three fundamental components of SDR: RF, Signal Processing, and User Interface. It describes common SDR setups, such as the Quadrature Sampling Detector (QSD) and WebSDR with various web clients, offering practical examples of how SDR works [[❞]](https://dh1tw.de/understanding-the-sdr-concept/) [[❞]](https://dh1tw.de/understanding-the-sdr-concept/) [[❞]](https://dh1tw.de/understanding-the-sdr-concept/) [[❞]](https://dh1tw.de/understanding-the-sdr-concept/) [[❞]](https://dh1tw.de/understanding-the-sdr-concept/) [[❞]](https://dh1tw.de/understanding-the-sdr-concept/).

These resources should provide a good starting point for understanding SDR demodulation at a basic level, suitable for someone with your background in software engineering but not in advanced mathematics.

 

[Unitrunker2]

I am relatively new ham - Tech in 2019. I am retired Software Engineer - many years as contractor at Robins AFB.
I am looking for simplified ("6th grade level") description of SDR demodulation.

Instead of calculus, how about trigonometry?

Each complex sample represents a phase angle and an amplitude. For FM, you care more about the angle than the amplitude. You can compute the angle with the arctan function. If you subtract the angles of two successive samples, you get a relative angle - that could be positive or negative. This relative angle is essentially the frequency deviation at that moment in time. These relative angles could be in degrees or radians (depends on which arctan function you use). Scale those to something suitable for your speakers and you have audio.

Above is greatly simplified by assuming the samples are already translated and pre-decimated before the demodulation. Hope you found it helpful.

 

[boatbod]

Unfortunately SDR is all about math, so although the formulas might make your eyes glaze over (they certainly do for me) you really need to take the time to study at least the basic concepts. Conversions between time and frequency domain, finite impulse response filters and convolutions performed on the sample streams are the basic sdr building blocks.