QuadRF: $499 Raspberry Pi SDR Sees WiFi Through Walls

Jeff Geerling’s hands-on review of the QuadRF landed at #2 on Hacker News this week with 507 points — because it does something that sounds implausible: a $499 device powered by a Raspberry Pi 5 that visualizes WiFi signals spatially, tracks drones in flight, and locates hidden wireless cameras, all as a live 30fps overlay you view from a phone or laptop. ScaleRF’s Crowd Supply campaign launched June 23, 2026, and ships September 30. This is not a toy SDR dongle. It’s a 4×4 MIMO phased-array radio platform with a fully open-source developer stack — and it’s gunning for equipment that costs 20 times as much.

How QuadRF Actually Sees Through Walls

The hardware is a Lattice ECP5 FPGA board with four patch antennas, connected to a Raspberry Pi 5 via two MIPI cables running at 5.6 Gbit/s. Those four antennas are phase-coherent: by measuring picosecond-level differences in signal arrival time across all four channels, the system calculates the direction of any RF source in its operating range. The result is rendered as a color-coded spatial overlay at 30fps — Wi-Fi access points, drones, wireless cameras, and beacons all show up as located objects, not just frequencies.

Geerling tested it with a DJI Mini Pro 4 flown behind his studio. QuadRF tracked the drone’s 5.8 GHz control link without difficulty, direction-finding it from inside the building. His father, a retired broadcast radio engineer, called the result “something we couldn’t do in professional labs without six figures of equipment.” One Hacker News commenter put it more bluntly: “It’s crazy to see super secret military tech from 30 years ago commoditized to a system cheaper than a gaming console.” That’s the story. ScaleRF has collapsed rack-mounted phased-array lab hardware into a single Raspberry Pi 5 board at $499.

The Developer Stack Is the Real Sell

The entire software stack ships under GPLv2/GPLv3: Linux drivers, SoapySDR support, calibration utilities, the browser-based RF camera interface, and example applications. The primary developer API is SoapySDR — the de facto standard for SDR hardware abstraction — with full Python and C++ support. Existing GNU Radio flow graphs, SDRangel setups, and SDR# pipelines connect to QuadRF without rewriting anything. The official documentation walks through complete working examples for both languages out of the box.

import SoapySDR
from SoapySDR import SOAPY_SDR_RX, SOAPY_SDR_CF32

sdr = SoapySDR.Device({"driver": "QuadRF"})
sdr.setSampleRate(SOAPY_SDR_RX, 0, 20e6)   # 20 MSPS, range: 1–80 MSPS
sdr.setFrequency(SOAPY_SDR_RX, 0, 5.8e9)   # 5.8 GHz
rxStream = sdr.setupStream(SOAPY_SDR_RX, SOAPY_SDR_CF32, [0, 1, 2, 3])
sdr.activateStream(rxStream)
# All 4 antenna channels streaming — de-interleave for beamforming

For headless or remote deployments, I/Q data streams over the network via SoapySDRServer, so you can run the QuadRF in the field and process signals on a workstation. Multiple boards tile together for square-meter scale phased arrays — useful for larger counter-UAS installations or research environments. The creator has an Analog Devices background (I/Q calibration for the AD93x series), and the hardware design reflects that: a 1-bit sigma-delta oversampling ADC achieves effective 8.5–9.5 ENOB across all eight ADC channels.

The Caveats Worth Knowing Before You Order

QuadRF operates from 4.9 to 6.0 GHz. That covers 5 GHz WiFi, drones, and most wireless cameras — but it does not cover 2.4 GHz WiFi, Bluetooth, LoRa (868 MHz / 915 MHz), Zigbee, or any other sub-5 GHz protocol. The Hacker News thread had a predictable refrain: “Please wake me up when they launch their LoRa version.” If your target protocol lives below 5 GHz, this isn’t your hardware today. ScaleRF hasn’t announced a lower-frequency variant.

The second caveat is actually a design feature. Passive radar — which uses ambient broadcast signals to track objects without emitting anything — is specifically controlled under ITAR at operating frequencies below 2 GHz. KrakenSDR had to remove its passive radar code after running into exactly this. ScaleRF took a different approach: proactively filed a detailed report with the State Department confirming QuadRF doesn’t exceed USML criteria, and deliberately omitted passive radar functionality. QuadRF does beamforming, which is what every 5 GHz WiFi router does. That’s a deliberate regulatory choice, not a missing feature.

Pricing and What You Get

The $499 main kit includes the QuadRF board, a Raspberry Pi 5, tripod, 32GB microSD, and power supply — everything needed to run out of the box. The $149 Mobile Expansion Pack adds field-deployable hardware. For researchers building larger arrays, the $594 Six-Pack includes six bare RF tiles without enclosure, antennas, or Pi 5 — but ships January 14, 2027. Comparable alternatives: KrakenSDR at $250 (direction finding only, no TX, no spatial visualization), ADALM-PHASER at $2,000+ (similar capability, narrower ecosystem). The $499 all-in price is competitive.

Key Takeaways

• QuadRF is a 4×4 MIMO phased-array SDR on a Raspberry Pi 5 that can visualize WiFi devices and drones spatially — in real time, through walls — for $499 including the Pi. Ships September 30, 2026.
• The developer stack is fully open source (GPLv2/GPLv3) with SoapySDR and GNU Radio integration. Existing Python and C++ SDR code works immediately with no SDK changes.
• The 4.9–6.0 GHz frequency range is the device’s hard limitation: no 2.4 GHz WiFi, no Bluetooth, no LoRa. Evaluate before ordering.
• ScaleRF proactively filed with the State Department to confirm USML compliance — avoiding the regulatory trap that caught KrakenSDR. Passive radar is excluded by design.