QuadRF phase-coherent – A new QuadRF project is building a phase-coherent four-channel SDR that pairs a dedicated RF board with a Raspberry Pi 5, enabling real-time “RF camera” scans across 4.9 GHz to 6.0 GHz. The software can visualize where signals are coming from, even overlaying
The breakthrough isn’t that radio direction finding is hard in theory. It’s that making the hardware behave well enough to do it in practice has always been a bottleneck—especially for anyone without lab-grade equipment.
QuadRF is trying to remove that friction. The project is building a phase-coherent four-channel SDR, designed to make direction mapping more accessible by letting its signals be measured across multiple antennas and processed coherently. The plan lives openly in a GitHub repository.
At the center of the build are two pieces of hardware: an RF board that handles reception and pre-processing. and a Raspberry Pi 5 that takes on additional processing. The RF board carries four patch antennas. Each patch antenna can operate across the 4.9 GHz to 6.0 GHz range. and each can be switched between right- or left-hand polarization.
For the on-device processing, QuadRF uses a Lattice ECP5 FPGA. It connects to the Raspberry Pi using two MIPI cables, linking directly to the camera and display interfaces. That setup is meant to support very high-speed data exchange. and once further processing is complete. the Pi can move data onward via Ethernet or Wi-Fi.
The hardware doesn’t stop at a single unit. Individual QuadRF boards can connect together in a lattice grid to form larger phased arrays, turning multiple four-channel systems into something bigger—at least in capability and scale—than one box on a desk.
But the project’s software is where the work starts to feel tangible. QuadRF is compatible with standard radio software such as GNU Radio, yet it also comes with programs of its own. The standout is an “RF camera.” Instead of working like a traditional scanner that produces readings you have to interpret. it scans the full frequency range at 30 fps. As signals are detected, it tracks their direction and renders them on a spatial plot.
Even more convincing is how that plot can be overlaid on a camera feed. When the visualization sits on top of a live image. it becomes easier to see radio signals emitted by nearby electronics. In the project’s own example. the creators tracked a drone in flight and went further—distinguishing the two radio transmitters on the drone.
This isn’t the first time multi-antenna SDR has appeared in the world of open hardware. QuadRF does add a twist though: it’s described as the first multi-antenna SDR that could transmit. That capability is also where caution comes in. The project notes that some uses of this kind of hardware run afoul of arms regulations. which is a reminder that “it can be built” doesn’t automatically mean “it can be used however you want.”.
The sequence from RF board to FPGA to Raspberry Pi to visualization is what makes the experience feel different. It turns phase-difference measurements into something you can look at—something that points back at the source rather than forcing you to do the math alone.
The QuadRF build is credited as being shared after a tip from [Swake], and its demonstration video is embedded as part of the project materials.
QuadRF SDR radio direction finding phased array Raspberry Pi 5 Lattice ECP5 FPGA RF camera GNU Radio 4.9 GHz to 6.0 GHz signal visualization drone tracking cybersecurity adjacent hardware