A $40 Software-Defined Radio

Digital radio enthusiasts immediately began adapting open-source tools that can translate I/Q information into audio and data streams. The result is a low-cost SDR that can pick up a huge variety of transmissions with different modulation schemes, including stereo FM from broadcasters, digital data packets from aircraft transponders, and single-sideband modulation (SSB) dispatches from amateur radio operators. Of course, the system isn’t as sensitive as purpose-built SDRs and is incapable of transmitting a signal, but it’s enough to see what’s going on across a huge chunk of spectrum.

Different receiver dongles pair the RTL2832U with different radio tuners, so the exact range of frequencies that can be received varies. I purchased a Freeview P250 dongle from a Chinese supplier on Amazon.com for $20, which included shipping. The P250 combines the RTL2832U with an Elonics E4000 tuner, allowing it to pick up signals from about 52 megahertz to 2.2 gigahertz, with a gap from about 1.1 to 1.25 GHz.

A small antenna came with the receiver, but I replaced it with a set of $15 rabbit ears from RadioShack. An adapter to connect the rabbit ears’ U.S. coaxial cable to the dongle’s European socket cost a couple of dollars.

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