Requirements
You need a hardware ADS-B radio receiver
The good thing is that these are readily available for purchase!
Either as a complete receiver dedicated to ADS-B, with a price range between $200 to $1000, or as a RTL-SDR USB Dongle for a DIY project, with a price range between $40 to $200 (available from various sources*).
If you opt to buy a complete receiver setup, ensure to pick a receiver that supports the generation of a JSON file with decoded ADS-B data that follows the Dump1090/Jetvision JSON format.
However, the most commonly used option is to build the receiver yourself using a single-board computer such as a Raspberry Pi. From $10 you can get a Pi Zero W, which is sufficient to run Linux and decode the ADS-B radio signals to generate a JSON file.
The macOS App ADS-B Radar needs this JSON file to display the aircaft & all other details on a map.
*) Ensure you get a dongle that supports ADS-B 1090MHz radio, usually with RTL2832 and R820T2 circuitry.
