QuadRF, the $499 gadget that reads your neighbor's WiFi through walls and tracks drones in real-time
QuadRF
QuadRF is a radio phased-array device that uses a Raspberry Pi 5 paired with a time-level picosecond FPGA board. The result is a device capable of applying advanced beamforming to radio signals, identifying hidden WiFi networks behind walls and tracking flying drones in real-time. It is not a military lab prototype but a kit that anyone can order online.
The operation utilizes four coherent antennas that measure the differences in signal arrival times, providing a live RF overlay at 30 frames per second on smartphones or laptops. WiFi devices, wireless cameras, drones, and beacons thus become color-coded radio sources based on frequency, within an operating range of 4.9 to 6 GHz.
The base kit costs $499 on Crowd Supply and includes four interchangeable dual-polarization antennas, a preloaded 32 GB microSD card, and a 27W power supply. A mobile expansion package adds a battery and a smartphone holder, allowing users to carry the device and analyze the RF environment on the go.
Behind the project lies the ambition for a radio array scalable to the Moon. QuadRF is developed by Martin McCormick, who previously worked at SpaceX on the team that created Dishy, the first Starlink terminal. The inspiration is clear: the stated goal of the project is to create a lunar-scale antenna array for Earth-Moon-Earth radio experiments and radio astronomy, chaining multiple QuadRF modules to achieve an EIRP of 1.15 MW in the most extreme configuration of 240 antennas.
In its current form, however, QuadRF remains a handheld device intended for local SDR applications. The transmission of I/Q data between the RF board and the Raspberry Pi 5 passes through the camera and display MIPI connectors, typically used for video peripherals, utilized here for over 5 Gbps of low-latency bandwidth. The team had to independently decode the MIPI protocol of the Pi 5's RP1 chip, leaving the PCIe connector free for high-speed storage or networking.
In practical tests, powering it on activates a WiFi hotspot to connect to for accessing a VNC interface via a browser, from which GNU Radio, SDR software, and an augmented reality viewer are launched. With the latter, a 5 GHz WiFi network on channel 100 appeared as a blue spot, while nearby networks showed up in red and green: however, the numerical scale of the values, in this still immature version, is not displayed on the screen.
The test with a DJI Mini Pro 4 drone flown behind the studio confirmed the tracking capability, although the lack of automatic gain control forced manual adjustment of sensitivity as the aircraft moved away. The crowdfunding campaign has already surpassed its expected goals, to the point that the team is transitioning from a 3D-printed shell to injection molding for mass production.
It should be noted that this is still pre-production hardware: like any crowdfunding campaign, promised delivery times are not a guarantee of adherence to deadlines.