Indeed very simple and within reach of a beginner.
Another illustration how RPi 2040 PIO is an exceedingly helpful thing. Without it, the RF-related circuits would have to use either bit-banging, or a bunch of small discrete components.
Certainly within reach of a beginner to build, but I wonder how many beginners would struggle to understand the details of a SDR. Knowledge of processors, memory, IQ sampling, DSP, etc. are not typical subject matter for beginners.
The original crystal radios were very simple, with a crystal (or later, a 1N34 diode), an optional (low Q) bandpass filter, and a piezoelectric earphone -- no batteries required. The principles of operation could be explained to a beginner in just a few minutes.
When I was a kid, I optimized my first "crystal" radio down to four components:
1) 1N34 diode.
2) 22k Ohm resistor (impedance matches the earphone).
3) Piezoelectric earphone.
4) Antenna wire (with alligator clip).
It worked well because there was only one radio station nearby. (KNX 1070, 50KW was about a mile away.)
By this token, the physics of semiconductors, which is required to explain how the crystal detector receiver works, is also uncommon knowledge among beginners!
Both computers and semiconductors can be explained qualitatively, bringing in the ideas like a one-way valve, or following written instructions. This, of course, would gloss over a ton of things, much like the optimized crystal radio blissfully lacks the RF filter in the audio frequency circuit: the mechanical properties of the earphone suffice.
"All models are wrong, but some are useful", as they say.
Another illustration how RPi 2040 PIO is an exceedingly helpful thing. Without it, the RF-related circuits would have to use either bit-banging, or a bunch of small discrete components.