Skip to content

Capturing LoRa signals using an RTL SDR device

Jump to bottom
rpp0 edited this page Nov 14, 2016 · 8 revisions

Capturing LoRa signals using an RTL-SDR device

This tutorial is intended for Software Defined Radio (SDR) beginners wishing to decode LoRa messages using gr-lora. We will be using a LoRa modem under our control in order to transmit messages, and an RTL-SDR to receive and display them back to the command line or Wireshark.

Prerequisites

Setup

As the first step we will build the GRC flow graph. Create a new flowgraph by selecting File > New > WX GUI. Since we're using an RTL-SDR, use drag the "RTL-SDR Source" block from the block tree panel to the grid view. Create a variable "freq" and set it to 868e6. Now configure the RTL-SDR block to use "freq" as its "Ch0 frequency", and set the "samp_rate" variable to 1 Msps. Finally, connect a "WX GUI FFT Sink" block to the "RTL-SDR Source" block for now, and set "Baseband freq" to "freq". The flowgraph now looks like this:

[Figure 1]

You can verify whether the LoRa modem is working correctly by transmitting a message at 868.1 MHz. If you have an RN2483 connected via serial over USB, you can do the following:

$ python
>>> from loranode import RN2483Controller
>>> c = RN2483Controller("/dev/ttyUSB0")
>>> c.set_sf(7)  # Set spreading factor 7
>>> c.set_cr("4/8")  # Set 4/8 coding
>>> c.send_p2p("00FF00FF")

A peak should appear centered at 868.1 MHz in the FFT plot during the transmission.

Configure gr-lora

Drag the "LoRa Receiver" block to the grid view. Configure it so that it matches the transmitter's configuration:

  • Spreading factor: 7
  • Sample rate: samp_rate
  • Frequency: freq
  • Offset: 868.1e6 - freq

Run the flowgraph

Finally, run the flowgraph and transmit a message with the LoRa device.

>>> c.send_p2p("FFFFFFFF")

The output should be printed to the terminal as shown below

[Figure 2]

Clone this wiki locally