Using Harmonics for Low-Cost Jamming
Vasilis Ieropoulos, Eirini Anthi
TL;DR
This paper demonstrates the feasibility of a low-cost, open-source RF attack using a Raspberry Pi to jam wireless conference microphones by exploiting harmonics of an unfiltered transmitter. Through identifying the target microphone's band (606–670 MHz), generating FM-modulated audio, and leveraging a 304 MHz carrier to produce a 2nd harmonic at the microphone frequency, the authors show successful interference across the 2nd–4th harmonics. They discuss mitigation strategies such as bandpass filtering and wired handshakes to counteract such attacks. The work highlights a practical security risk posed by inexpensive, readily available hardware and underscores the need for robust RF defenses in educational and organizational settings.
Abstract
The digitalisation of the modern schooling system has led to multiple schools and organisations buying similar hardware. Electronic equipment like wireless microphones, projectors, touchscreen displays etc., have been almost standardised with a few well-known brands leading the market. This has led to the adoption of common frequency ranges between brands with many sticking between 600-670 MHz. The popularity of low-cost computing devices like the Raspberry Pi which has been used in a plethora of applications has also taken the path of being used as low-cost transmitters. There have been many implementations where the Raspberry Pi has been used as the target device but few cases where the PI is the actual threat. In this paper, we explore the use of the Raspberry Pi as a stealth radio frequency jamming device to disable wireless conference microphones. Harmonics were used to achieve frequencies outside the Pi's transmission frequency by taking advantage of its unfiltered transmission.