In the world of radio waves, traditional systems rely on components like resistors, capacitors, and coils to build circuits that process signals.
For those of us who just want to explore radio without dealing with bulky, expensive components, and the technical know-how to modify them, digital technology comes to the rescue, letting us dive into the realm of radio frequencies for almost nothing 🎉.

The idea is to digitize the radio signal as early as possible so it can be processed by a CPU. This lets you apply more complex algorithms, especially using complex numbers, which can be a headache to implement with just analog components.
Yes, those famous complex numbers you thought were useless in high school turn out to be very useful for digitizing signals.

This simplifies many mathematical operations.
Not convinced? Consider multiplying two signals (you don't need to know all the details).
Without complex numbers, you’d have to perform some pretty twisted trigonometric calculations. With complex numbers, you simply multiply the amplitudes and add the phases, done easily with basic algebra.

Plus, digital systems update in real time, which is great for software and algorithms.
Another major advantage of digital is the ability to visualize the frequency spectrum and produce a spectrogram (often called a waterfall), which is very useful for understanding what's happening.

It's like using Wireshark to analyze network packets 🦈.

Radio signals are analog and contain an infinite range of values, something our CPUs don’t like. So we sample the signal at regular intervals, converting it into a finite series of numbers.
Essentially, we measure the signal's amplitude at regular points and record those values. This is called the sampling rate!
This process is enabled by an Analog-to-Digital Converter (ADC).
The more samples you take, the more accurately the digital signal represents the real one, but the data becomes larger and takes longer to process.

There's also the Nyquist–Shannon theorem which states that to faithfully reconstruct an analog signal, you must sample at least twice its maximum frequency.

Digitizing and processing signals via software is known as SDR (Software Defined Radio).
This is made possible by receivers like the one shown below:

These affordable receivers (check out this great starter kit) connect to a computer via USB and run SDR software (there are several options available).
They usually incorporate an MCX (Micro Coaxial eXtended) connector, a smaller coaxial plug, to connect your antenna.
Note that these receivers only support signal reception; for transmission, devices like the HackRF are required.

Once you have an SDR receiver, you just need SDR software. My personal favorite is SDR++ for general listening.
Other notable options include SatDump, which is essentially SDR++ but specialized for receiving and decoding satellite signals, and SDRAngel, which comes with plugins for displaying interactive maps, ideal for applications like ADS-B reception.

Also, there’s the DragonOS Linux distribution (DragonOS), which comes pre-installed and configured with all these SDR tools.