This document discusses software defined radio (SDR) and various low-cost SDR devices that can be used for experimenting with radio signals, including RTL-SDR USB dongles, HackRF, NooElec SDR sticks, and FUNcube Dongles. It provides information on software like GNU Radio, Gqrx, rtl-sdr library, ViewRF, and OpenBTS for processing radio signals on devices like the BeagleBone Black.