In the quick start guide for Software Defined Radio (SDR) on Linux we will listen to some very common frequencies using a RTL-SDR. SDR is a radio communication system where traditional hardware components are instead implemented in software. Some common low-cost DVB-T USB dongles with the Realtek RTL2832U controller and tuner can be used as a wide-band SDR receiver.
Start by installing the required packages for downloading and compiling the
rtl-sdr package. The
libusb-1.0-0-dev package provides a C library used for accessing USB devices (e.g. the RTL-SDR).
sudo apt-get install git cmake build-essential libusb-1.0-0-dev
After retrieving the required packages you will be able to clone, build and compile the RTL-SDR Osmocom drivers from source.
git clone git://git.osmocom.org/rtl-sdr.git cd rtl-sdr/ mkdir build cd build cmake ../ -DINSTALL_UDEV_RULES=ON make sudo make install sudo ldconfig sudo cp ../rtl-sdr.rules /etc/udev/rules.d/
The RTL-SDR is normally used as a TV device and doesn’t work for SDR purposes if we don’t block the default drivers. Create a file called
/etc/modprobe.d/blacklist-rtl.conf using root privileges with the following content:
Save the file and reboot your system. You can test the RTL-SDR by running the following command
rtl_test -t. The output will look similar to this:
Found 1 device(s): 0: Realtek, RTL2838UHIDIR, SN: 00000001 Using device 0: Generic RTL2832U OEM Found Rafael Micro R820T tuner Supported gain values (29): 0.0 0.9 1.4 2.7 3.7 7.7 8.7 12.5 14.4 15.7 16.6 19.7 20.7 22.9 25.4 28.0 29.7 32.8 33.8 36.4 37.2 38.6 40.2 42.1 43.4 43.9 44.5 48.0 49.6 [R82XX] PLL not locked! Sampling at 2048000 S/s. No E4000 tuner found, aborting.
Gqrx is an open source software defined radio receiver. The package has been included in Ubuntu for many years, but you probably want to install a newer version using the official personal package archive (PPA).
sudo add-apt-repository -y ppa:bladerf/bladerf sudo add-apt-repository -y ppa:myriadrf/drivers sudo add-apt-repository -y ppa:myriadrf/gnuradio sudo add-apt-repository -y ppa:gqrx/gqrx-sdr sudo apt-get update sudo apt-get install gqrx-sdr
It is recommended that you also install the
libvolk1-bin package and run
volk_profile tool to optimize GNU Radio performance on your own computer.
sudo apt-get install libvolk1-bin volk_profile
On the first startup of Gqrx you will need to configure your device using the following settings:
Device: Realtek RTL2838xxx Device string: rtl=0 Input rate: 1800000 Decimation: None Bandwidth: 0 MHz LNB LO: 0 MHz
Note: you can always change your device configuration by clicking the circuit board icon in the menu.
Lookup the frequency of one of your local radio stations and update the frequency in the Receiver Options tab on the right side of Gqrx. Don’t forget to set the mode to WFM (mono) or WFM (stereo). You might need to change the gain in order to hear something.
P2000 is a one-way communications network for pagers based on the FLEX-protocol developed by Motorola. The P2000 network is used by the emergency services in the Netherlands. The FLEX-protocol does not provide encryption, so you can read the messages yourself using an RTL-SDR.
In order to receive and decode the FLEX messages we will be using
multimon-ng, which can be installed from source:
git clone https://github.com/EliasOenal/multimon-ng.git cd multimon-ng mkdir build cd build cmake .. make sudo make install
Connect your RTL-SDR and run the following command to receive the FLEX messages send on the P2000 network.
rtl_fm -f 169.65M -M fm -s 22050 | multimon-ng -a FLEX -t raw /dev/stdin
Note: it might take several minutes before you start receiving any message, you can always check an online P2000 feed for messages appearing in your local region.
Air traffic monitoring
You can monitor air traffic using an RTL SDR and the
dump1090 package. Start by downloading and compiling the
git clone https://github.com/MalcolmRobb/dump1090.git cd dump1090 make
To run dump1090 in interactive mode, with networking support, you will need to run the following command:
./dump1090 --interactive --net
Open your browser and open http://localhost:8080/ to see live air traffic:
Raspberry Pi as a RF transmitter
rpitx package you can turn your Raspberry Pi in a simple radio frequency transmitter. It will be able to handle frequencies between 5KHz and 1500MHz. This includes some common frequencies (e.g. 433MHz).
Note: it might not be legal to transmit on all available frequencies, check your local regulations before transmitting anything!
You will need to plug a wire on GPIO 4, which will act as the antenna. I’ve used a cheap breadboard cable (see the picture below). The optimal length of the wire depends on the frequency, but a few centimeters should be fine for local testing.
After installing Raspbian you can install the
rpitx package using the following commands.
git clone https://github.com/F5OEO/rpitx cd rpitx ./install.sh sudo reboot
After rebooting the Raspberry Pi you can go to your rpitx folder and launch
cd rpitx ./easytest.sh
Using your SDR receiver you will be able to monitor the transmitted signals. Try to send the some test signals on the 434 MHz, the rpitx default band.