Detecting Drones and Visualizing WiFi: An Overview of QuadRF

The QuadRF is a sophisticated phased-array radio system. At its core, it leverages a Raspberry Pi 5 paired with an FPGA board capable of timing precision at the picosecond level.

A sobering thought: If the open-source community can develop a tool with these capabilities, the tools available to national governments are likely far more advanced.

While software like Wireshark allows users to inspect hidden traffic on a wired network, WiFi packets travel through the air. This means snooping is possible without any physical connection to the hardware. The QuadRF provides the software necessary to stream and decode these RF signals, which can then be exported to high-performance computers for deep traffic analysis. Rather than banning such tools, it is more productive to expose security flaws and understand the current landscape of RF surveillance.

From Handhelds to the Moon

The project was conceived by Martin McCormick, a former SpaceX engineer who worked on "Dishy" (the original Starlink terminal). McCormick is envisioning a much larger application for this technology: a Moon-scale antenna array. This massive system would be used for radio astronomy and EME (Earth-Moon-Earth) experiments.

The Scaling Vision

While the handheld version is designed for local SDR (Software Defined Radio) applications, licensed operators could theoretically link multiple QuadRF modules to achieve a massive directional gain of up to $1.15 \text{ MW EIRP}$.

Hardware Specifications

Hands-On Testing

After pre-ordering a kit, I received a prototype to test alongside my father, a retired broadcast radio engineer. While the user interface is still 3D printed (moving toward injection molding) and a bit unpolished, the performance is impressive.

The User Experience

1. Boot Sequence: The Pi 5 starts and broadcasts a WiFi hotspot.
2. Access: Users connect via a browser-based VNC session.
3. Software Suite: Access to GNU Radio, various SDR tools, and a custom AR RF Visualizer.

The AR visualizer represents RF frequencies as colorful "blobs" overlaid on a camera feed. During my tests, my 5 GHz WiFi network (operating on Channel 100, $\approx 5.5\text{ GHz}$) appeared as a light blue mass.

Field Test: Drone Detection

Using the Mobile Expansion Pack (which adds a battery and phone mount), we tested the device against a DJI Mini Pro 4.

• Successfully spotted the drone in the sky.
• Tracked the drone as it flew away.
• Improvement needed: The manual gain control is clunky; an Automatic Gain Control (AGC) system would be a significant upgrade.

The Technical Edge: MIPI vs. USB

The most innovative part of the QuadRF is how it handles data. Instead of using USB, it utilizes the Raspberry Pi's MIPI lanes (typically used for cameras and displays) to stream I/Q (In-phase/Quadrature) data.

// Conceptual data flow for QuadRF
RF_Signal -> FPGA_Processing -> MIPI_Interface -> RP1_Chip -> Pi5_CPU

Why MIPI?

• Bandwidth: It supports data rates exceeding $5 \text{ Gbps}$.
• Latency: Extremely low latency, full-duplex transfer.
• Efficiency: It adds virtually no cost to the RF board and prevents sample loss.
• Flexibility: By using MIPI, the PCIe connector remains open for high-speed NVMe storage or advanced networking.

The team essentially reverse-engineered the MIPI protocol on the Pi 5 to allow for this high-bandwidth streaming. This architecture also enables the "daisy-chaining" of modules, where each unit calculates its own phase shift.

Final Thoughts

As with any crowdfunding project, buyers should manage their expectations regarding delivery timelines. However, despite the early-stage UI, the QuadRF is a powerhouse of a tool. It transforms the invisible RF environment into something visual and tangible, and I am eagerly awaiting the arrival of my production unit.