These days, we are spoiled for choice with regard to SDRs for RF analysis, but sometimes we’re more interested in the source of RF than the contents of the transmission. For this role, [Drew] created the RFListener, a wideband directional RF receiver that converts electromagnetic signal to audio.
The RF Listener is built around a AD8318 demodulator breakout board, which receives signals using a directional broadband (900 Mhz – 12 Ghz) PCB antenna, and outputs an analog signal. This signal is fed through a series of amplifiers and filters to create audio that can be fed to the onboard speaker. Everything is housed in a vaguely handgun shaped enclosure, with some switches on the back and a LED amplitude indicator. [Drew] demonstrates the RFListener around his house, pointing it at various devices like his router, baby monitor and microwave. In some cases, like with a toy drone, the modulation is too high frequency to generate audio, so the RF listener can also be switched to “tone mode”, which outputs audio tone proportional to the signal amplitude.
The circuit is completely analog, and the design was first done in Falstad Circuit Simulator, followed by some breadboard prototyping, and a custom PCB for the final version. As is, it’s already an interesting exploration device, but it would be even more so if it was possible to adjust the receiver bandwidth and frequency to turn it into a wideband foxhunting tool.