An undocumented command buried in the Semtech LR2021's ROM is the key to LR2021-SDR, a new open-source project by developer Samuel Reynolds that converts the LoRa transceiver into a wideband software-defined radio. By exploiting this hidden instruction on chips running ROM 1.24, the firmware exposes raw 16-bit I/Q samples over SPI, letting software decode signal types the chip was never designed to handle: P25 Phase 1 digital voice, POCSAG pager messages, and analog FM. The experimentally verified receive range spans 100 MHz to 2.74 GHz, well beyond the datasheet's specified 150 to 960 MHz and 1.5 to 2.5 GHz bands.
Continuous I/Q capture runs reliably at 125,000 complex samples per second for up to 391 seconds with no reported FIFO loss, and short bursts can hit 250,000 samples per second. Pushing beyond that to 500,000 or 1,000,000 samples per second causes overflows because the 16 MHz SPI bus can't keep up. The project also includes experimental transmit support, with successful tests sending P25 voice frames, temperature sensor data picked up by rtl_433, and OOK/FSK remote control signals that a Flipper Zero decoded on the other end. Continuous transmission and live voice TX remain under development.
The practical payoff comes through LakeShark, Reynolds' companion firmware that turns the LilyGO T-Display P4 into a handheld SDR scanner. The T-Display P4 pairs an ESP32-P4 RISC-V dual-core processor with a 10.4 cm (4.1 inch) AMOLED touchscreen, GPS, and an onboard LR2021 transceiver. Previously, LakeShark required an external RTL-SDR dongle for signal reception. With LR2021-SDR integrated, the board can now receive and decode P25, POCSAG, and FM signals using nothing but its built-in radio hardware.
This is the third open-source SDR hack to surface in October 2026 alone, following projects that repurposed an ESP32-S3 as a 2.4/5 GHz SDR transmitter and a Gemtek Wi-Fi 7 router as a 320 Msps wideband receiver. The LR2021-SDR source code is available under the GPL-3.0 license and includes a C library, standalone ESP32-P4 capture firmware, and Python analysis tools. The T-Display P4 with the LR2021 LoRa module starts at around $100 (€92) for the TFT variant and $125 (€115) for the AMOLED version. The project requires an LR2021-equipped board with an appropriate antenna, and results may vary across individual hardware units since testing has only been performed on a single board so far.
