Recapping Part 1
Welcome to Part 2 of our guide for setting up the Raspberry Pi 3B+ for Software Defined Radio (SDR).
When we left off in Part 1, we had just successfully booted the Raspbian Buster operating system on the Raspberry Pi 3B+. We did not yet use the radio receiver: the RTL-SDR dongle. But by now, I’m assuming you already have a microSD card running the appropriate version of the Raspbian Operating system, and that your own Raspberry Pi will boot successfully to the graphical desktop.
Objective
Here in part 2, we will:
- Configure the Raspberry Pi so we can get the most out of it and its peripherals
- Update the system to get the latest software packages
- Install dependencies (prerequisite software) for running rtl-sdr
- Install the rtl-sdr application from source. This is the suite of applications that will receive radio broadcasts from the RTL-SDR dongle and then pipe the audio out to the amplified speakers
If you are new to Linux operating systems, note that the text-only console environment is case-sensitive. So be prepared to copy text commands verbatim, and double-check your use of uppercase and lowercase.
When it’s all said and done, we will have a functioning SDR that can tune into wideband frequency modulation (FM or WBFM) broadcasts.
Configuring Raspbian
The first thing we need to do is configure the Raspbian operating system. Most of the settings we deal with can be adjusted later if needed, but its best to get them right the first time and set the stage for an easy setup experience.
If you plan to connect your Raspberry Pi to the Ethernet with a wired cable to your router, you should do so now.
Go ahead and power on the Raspberry Pi if you haven’t already.
Set Country
Here, you should configure your time zone, language, and your preferred keyboard type.
If you are used to the American style keyboard (which lacks the £ symbol), then this is something you don’t want to answer incorrectly. You need the correct keyboard setting to use the text-only console in future steps.
Change Password
Here, you need to create and confirm a strong and memorable password. This is something you don’t want to forget.
Set Up Screen
Here is where your situation may be very different from mine. In my build, I am using a Newhaven Display International HDMI display with an 800 x 480-pixel resolution. Raspbian did not detect this automatically, and until I configure it in a later step, the right-hand side of my display will be undrawn.
Normally, I would follow instructions and fix this by checking the “This screen shows a black border…” option. But my monitor came with some special setup instructions from the manufacturer’s website that I will have to configure later in the console.
Select Wi-Fi Network
If you aren’t using a wired Ethernet connection, then select your Wireless network. Then prepare to enter your login credentials for the wireless network. I should note that having metal in the proximity of the Raspberry Pi may hurt your reception, so take this into consideration.
Update Software
Within a minute or so, your Raspberry Pi should have access to your wireless network and the internet.
Next, Raspbian will offer to automatically update its software packages and language support.
This updating step can be a lengthy process. I would allocate around 30 minutes to this in your schedule. So it may be a good time to take a short break, move around a bit or otherwise let the system run its course.
Reboot
When the system completes its updates, you should be able to reboot. You can do this by clicking the raspberry icon in the top-left corner of the desktop. Then navigate to the very bottom of the menu, and tap or click: Shutdown –> Shutdown.
Reboot the Raspberry Pi 3B+.
Raspi Configuration
After the system reboots and the desktop is restored, click the Console icon near the top of the desktop as shown in the figure below.
While the console opens, start the Rasbpian configuration tool by typing the following into the console:
sudo raspi-config
This should open the configuration tool.
Use the arrow keys to navigate this application in the following steps…
Expand the File System
To get the most out of the microSD card, expand the file system. Navigate to Advanced Options –> Expand File System. This change will take effect after the next reboot.
Set Audio Output
Next, navigate to: Advanced Options –> Audio
This is where you should select the appropriate audio output method for your setup. In my case, I want all of my audio directed to the 3.5 mm stereo audio jack, but Raspbian has the option to send audio over HDMI if that suits you.
You can change this setting later if needed, so select your preference accordingly.
Video Configuration
Finally, there’s the issue of my screen resolution. By default, Raspbian selected a 640 x 480 format for me. This was intended for a screen with a different aspect ratio.
Navigate to: Advanced Options –> Resolution
For me, there was no option to use 800 x 480. This is fine for now because I can add a special configuration for my display in a later step. So for now, I will not make changes here. If you see an option that works better for your display, you may want to select it here and now.
Reboot
Return to the raspi-config main menu, and then select “Finish” and select “Yes” under “Reboot Now?”
Let the Pi reboot again.
Special Video Configuration
Let the system boot back to the desktop. If your display looks okay, you can skip this step and proceed to the Audio Test section below.
As I mentioned, I am using the Newhaven Display NHD-7.0-HDMI-N-RTXL-CTU and I want to expand the desktop to use the entire width and height of this display. The official user guide says I need to open a boot configuration file and make some adjustments.
Open the console, and then enter:
sudo nano /boot/config.txt
This will open a text editor called nano. If you’re not familiar with Linux or Nano, I will warn you right now not to use CTRL+C, CTRL+X, or CTRL+V for copying, cutting, or pasting in this environment. Those key combinations will have other results. Instead, cut and paste by right-clicking to bring up the menu.
Within this file, I need to add the following lines of text:
hdmi_group=2
hdmi_mode=87
hdmi_cvt=800 480 60 6 0 0 0
I have chosen to enter this directly below the line that says “#hdmi_mode=1.”
When you are done, save your changes by pressing CTRL+O. Then press CTRL+X to exit GNU Nano.
Reboot again, and the desktop should now span the entire display. Nice!
Test the Audio
Now is a good time to make certain the audio is working. Plug in your amplified speakers or turn up the volume on your HDMI device if it supports audio (depending on your audio preference from the previous steps).
The audio levels out of the 3.5 mm stereo port are intended for amplification and will not drive speakers or earbuds to useful levels of loudness. So instead, I am using a pair of PC speakers with a power supply and an audio amplifier built-in.
If you have installed the full version of Raspbian, then you should have no trouble accessing the web by clicking the blue globe icon on the top toolbar. This will open the Chromium browser, which you can use to test the audio.
Installing Dependencies
Now its time to start installing the applications to run the RTL-SDR dongle. Speaking of which, if you haven’t already plugged in your RTL-SDR receiver, shut down Raspbian and plug it in. Note that if your 5-volt supply to the Raspberry Pi 3B+ is under-sized, the Raspberry Pi may reboot suddenly when you plug in the RTL-SDR, which is why I shut it off first.
When the desktop launches again, open the console.
To be 100 % sure the update we did in earlier steps completed, do another round of updates with the following commands:
sudo apt-get update
sudo apt-get upgrade
Next, use GNU nano again to create a file called no-rtl.conf…
sudo nano /etc/modprobe.d/no-rtl.conf
Using the GNU Nano editor, add the following lines of text to the no-rtl.conf file…
blacklist dvb_usb_rtl28xxu
blacklist rtl2832
blacklist rtl2830
Now save it by pressing CTRL+O. Then exit the GNU Nano editor by pressing CTRL+X.
Reboot
Now reboot the system.
Install Dependencies
Now it’s time to install the software dependencies for rtl-sdr. Reopen the console and perform the following installations.
sudo apt-get install git-core
sudo apt-get install git
sudo apt-get install cmake
sudo apt-get install libusb-1.0-0-dev
sudo apt-get install build-essential
Now, copy the latest version of the rtl-sdr code from the Git repository:
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
cd ~
sudo cp ./rtl-sdr/rtl-sdr.rules /etc/udev/rules.d
sudo mv no-rtl.conf /etc/modprobe.d
Reboot
Reboot the system one last time.
Test and Use the RTL-SDR with Audio
When the desktop boots again, return to the console and enter the following…
rtl_test
This should yield something resembling the following…
Congratulations! You should now have a working RTL-SDR receiver.
Let’s take things one step further by piping a little audio to the speakers/display. Press CTRL+C to terminate the rtl_test application.
Then enter the line below into the console. The number “101500000” in this line should correspond to the frequency (in Hz) that you wish to receive. In my case, 101.5 MHz is the center frequency for a local, powerful WBFM station in my listening area. But your situation may be different…
rtl_fm -M wbfm -f 101500000 | aplay -r 32000 -f S16_LE -c 1
Entering this yields not only the following screen, but also plays the demodulated audio from the amplified speakers…
Coming Up in Part 3…
Congratulations on making it this far, and we hope you found this helpful. If you have feedback, feel free to reach us via our contact page, as we welcome constructive criticism.
Luckily, the hardest parts are now behind us. In the next part, we will install the graphical SDR program: GQRX.
References
| [1] | B. R. Mayes, “Software Defined Radio for Raspberry Pi 3B+ (Part 1),” 24 Nov. 2019. [Online]. Available: https://unboxing-tomorrow.com/software-defined-radio-for-raspberry-pi-3b-part-1/. [Accessed 1 Dec. 2019]. |
| [2] | Raspberry Pi Foundation, “Audio configuration,” Raspberry Pi Foundation, [Online]. Available: https://www.raspberrypi.org/documentation/configuration/audio-config.md. [Accessed 25 Nov. 2019]. |
| [3] | Newhaven Display International, “7.0” HDMI TFT Modules,” 2018. [Online]. Available: http://www.newhavendisplay.com/userguides/NHD-7.0-HDMI-N_User_Guide.pdf. [Accessed 30 Nov 2019]. |
| [4] | floehopper, “Install rtl-sdr on Raspian on Raspberry Pi,” GitHub Gist, [Online]. Available: https://gist.github.com/floehopper/99a0c8931f9d779b0998. [Accessed 1 Dec 2019]. |
| [5] | “Stack Exchange | File Manager instantly closes when opened,” Stack Exchange, 24 Dec. 2018. [Online]. Available: https://raspberrypi.stackexchange.com/questions/92213/file-manager-instantly-closes-when-opened. [Accessed 26 Nov. 2019]. |
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