[jcims]

The challenge is that the raspberry pi doesn't have an analog to digital converter with enough bandwidth to sample the ADS-B data, or any way to downconvert the signal from 1090MHz to see it to begin with, so you are going to need hardware.

ADSB uses pulse amplitude modulation, so if you built or bought a downconverter and amplifier, you might be able to pick up the modulation by sending the downconverted/amplified signal to a GPIO pin and reading its state at say 5-10 MHz.

It'd be pretty messy and you'd have to write the demodulator from scratch, but might be able to pickup the frame decoding from one of the other products out there to actually read the content.

Would be a really fun project but not likely to save money and definitely not time.

[OrangeMango]

Excellent comment, thank you :)