RTL SDR dongle

board ID radio OS support deployment
rtl-sdr Saclay 3

RTL-SDR is cheap USB dongle that allows to perform software defined radio (SDR) on frequences between 500kHZ to 1.75GHz. This kind of device can only be used in reception mode.

You can find useful information on the rtl-sdr.com website.

Usage on IoT-LAB

In IoT-LAB, we provide remote access to the rtl-sdr data using the rtl_tcp daemon running on the gateway on which the dongle is plugged. The rtl_tcp daemon is configured to listen on port TCP:50000 and you can access it once an experiment is running on a rtl-sdr device.

Access can be done by opening an SSH tunnel on port 50000 between your computer and the rtl-sdr in IoT-LAB. Just use the following command:

$ ssh -L 50000:rtl-sdr-<id>:50000 <login>@saclay.iot-lab.info

You have to keep the SSH session opened during the experiment.

Connect to the RTL-SDR dongle using GNU radio

To retrieve the radio signal, the easiest way is to use GNU Radio.

Install GNU radio

GNU Radio can be installed by following the official documentation.

To retrieve the radio signal from the RTL SDR dongles, you will also have to install the osmosdr plugin.

On a Debian-like system like Ubuntu, you can install both GNU Radio and osmosdr with the following commands:

$ sudo apt install gnuradio gr-osmosdr

Example of GNU radio setup

Here we provide an example of GNU radio workflow that allows to retrieve and display the RTL-SDR radio signal.

  1. Download this sample GNU radio project
$ wget https://iot-lab.github.io/assets/misc/docs/rtl-sdr/rtl_tcp.grc
  1. Start gnuradio-companion and open the project file you just downloaded:
$ gnuradio-companion rtl_tcp.grc

You should end up with the following user interface:

Note: See the Device Arguments field in the RTL-SDR source box: it points to rtl_tcp=127.0.0.1:50000. This is how the signal is retrieved from the RTL SDR dongle in IoT-LAB via the SSH tunnel that you have to open before.

Test this setup

Let’s submit an experiment with one rtl-sdr and one LoRa board in the Saclay site.

To send LoRa radio messages with the LoRa board, we will a prebuilt firmware that can be downloaded from here:

$ wget https://iot-lab.github.io/assets/firmwares/rtl-sdr-lora.elf

The experiment can be submitted as follows:

$ iotlab-experiment submit -d 120 -l 1,site=saclay+archi=rtl-sdr:none -l 1,site=saclay+archi=st-lrwan1:sx1276,rtl-sdr-lora.elf
$ iotlab-experiment wait

You can print the information about your experiment to get the <id> of your devices (lora board and rtl-sdr dongle):

iotlab-experiment get --print
{
    "effective_duration": 3,
    "firmwareassociations": [
        {
            "firmwarename": "eae328082baa20476a32251f1f963e8d_rtl-sdr-lora.elf",
            "nodes": [
                "st-lrwan1-<id>.saclay.iot-lab.info"
            ]
        }
    ],
    "id": <experiment id>,
    "name": "",
    "nb_nodes": 2,
    "nodes": [
        "rtl-sdr-<id>.saclay.iot-lab.info",
        "st-lrwan1-<id>.saclay.iot-lab.info"
    ],
    ...
}

Open the SSH tunnel between your computer and the RTL-SDR dongle:

$ ssh -L 50000:rtl-sdr-<id>:50000 <login>@saclay.iot-lab.info

Start GNU radio and launch the workflow with the icon:

$ gnuradio-companion rtl_tcp.grc

The following window with the waterfall and spectrogram windows should appear:

Now, let’s connect to the lora board serial port from the terminal running the SSH tunnel:

<login>@saclay:~$ nc st-lrwan1-<id> 20000
main(): This is RIOT! (Version: 2020.04)
Welcome to RIOT!
>

Using ifconfig command of the RIOT shell, check the radio configuration of the LoRa interface on the board:

> ifconfig
ifconfig
Iface  4  Frequency: 868299987Hz  BW: 125kHz  SF: 12  CR: 4/8
           TX-Power: 14dBm  State: SLEEP
          L2-PDU:6911

The frequency is 868299987Hz so it should be adapted to be within the GNU radio listen window:

> ifconfig 4 set freq 868200000
ifconfig 4 set freq 868200000
success: set frequency [in Hz] on interface 4 to 868200000
> ifconfig
ifconfig
Iface  4  Frequency: 868199951Hz  BW: 125kHz  SF: 12  CR: 4/8
           TX-Power: 14dBm  State: SLEEP
          L2-PDU:6911

Using the txtsnd command, you can send raw LoRa radio packets and see them appear in the GNU Radio interface:

> txtsnd 4 bcast "Hello RTL SDR!"