tl;dr: QuadRF is an open-source handheld phased-array SDR built on a Raspberry Pi 5 and FPGA, covering 4.9–6 GHz and using the Pi's MIPI lanes for >5 Gbps I/Q streaming. It can visualize WiFi signals through walls in AR, track drones in flight, and daisy-chain with other modules—part of a larger project aiming at a Moon-scale antenna array for EME experiments. Available on Crowd Supply starting at $499; the UI is rough but the hardware reportedly works impressively well.