# LR2021-SDR turns Semtech LoRa chip into 100 MHz–2.74 GHz software-defined radio

> **Key takeaway:** An open-source project by Samuel Reynolds uses an undocumented ROM command to expose raw I/Q samples from the Semtech LR2021 LoRa transceiver, turning it into a wideband SDR without external hardware.

**Published:** 2026-10-20T07:00:17+00:00 
**Source:** CNX Software 
**Category:** open-hardware 
**Canonical URL:** https://fosswire.org/news/lr2021-sdr-turns-semtech-lora-chip-into-100-mhz274-ghz-softw.html 

## Summary
The LR2021-SDR project unlocks raw baseband access on the Semtech LR2021 LoRa transceiver, enabling reception and transmission across 100 MHz to 2.74 GHz—well beyond the chip's documented bands. The GPL-3.0-licensed firmware captures 16-bit I/Q samples over SPI at up to 250,000 complex samples per second, allowing software decoding of P25 digital voice, POCSAG pager traffic, analog FM, and Bluetooth LE advertising. The project includes ESP32-P4 standalone firmware, Python tools, and integration with the developer's LakeShark handheld scanner firmware.

## How the LR2021-SDR bypass works
- **Undocumented ROM command**: The project uses a command in ROM version 1.24 to bypass the LR2021's normal packet-processing pipeline and expose raw 16-bit I/Q samples directly from the baseband
- **SPI bottleneck**: 16 MHz SPI limits continuous capture to 125,000 samples/s; 250,000 samples/s works for short bursts, but 500,000+ causes FIFO overflows
- **Hardware limitation**: Only LR2021 with ROM 1.24 is supported; the SX1262 variant lacks raw I/Q access capability
- **Verification method**: Reception confirmed at 100 MHz, 1.3 GHz, 2.6 GHz, and 2.74 GHz using clock harmonics and HackRF One signals in a shielded enclosure
- **Transmission status**: Experimental burst transmission works (P25 test tones, OOK/FSK remote control, temperature sensors); continuous TX and live voice remain under development

## Why it matters
The project eliminates the need for an external RTL-SDR dongle in embedded devices already carrying an LR2021, potentially lowering cost and power consumption for handheld scanners and IoT gateways. However, results are from a single tested board and lack calibrated sensitivity measurements, limiting immediate production use.