Smaller radio systems can be covered using a Raspberry Pi. If you are interested in doing this, you should really get a Pi 4 or better yet, a Pi 5. It maybe possible to get things running on an older Pi, but you often get unexpected behavior and errors. A Pi 4 can handle 3-4 simultaneous recordings. Make sure you have a good power supply. Also pay attention to heat. If the Pi gets too hot, it will slow down. A good case or fan can help keep it going full tilt.

Trunk Recorder uses ffmpeg for concluded call audio processing, including WAV concatenation, optional filtering/normalization, and optional M4A creation.

RaspberryOS (aka Raspbian)

Setup Raspbian

This is a good guide on how to setup a Raspberry Pi in headless mode. This means that you do not have to attach a monitor, keyboard or mouse to it to get it working. The steps below are pulled from this guide.

Download and burn the image

The first step is to put the Raspberry Pi OS onto a MicroSD card. You will need to have a USB MicroSD card adaptor, so you can connect it to your computer. Either of these approaches should work:

• Download the Raspberry Pi OS Lite image.
• Install Raspberry Pi OS using Raspberry Pi Imager which can download and burn the image above.

Setup for headless boot

After the OS has been written to MicroSD card, we need to change a few files so that the Pi can get on Wifi and also allow for SSH connections. See the guide for how to do it using Windows.

• On a Mac touch /Volumes/boot/ssh
• Next, add the WiFi info
  • nano /Volumes/boot/wpa_supplicant.conf

country=US
ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1

network={
ssid="NETWORK-NAME"
psk="NETWORK-PASSWORD"
}

• Eject the MicroSD card (first in the OS and then physically from the reader)
• Put the MicroSD card in the Pi and power it on.

Remote Access

This is a good guide for how to find and connect to a Pi on your network.

These steps should work on a Mac and assume you only have one Pi on the Network

• Check to see if it is up: ping raspberrypi.local
• Clear old known hosts: ssh-keygen -R raspberrypi.local
• See if you can connect: ssh pi@raspberrypi.local *default password is: raspberry *
• Exit: exit
• Create your SSH keys if you don't have them yet: ssh-keygen
• Send over you keys: ssh-copy-id pi@raspberrypi.local

Setup

The following steps setup all of the libraries needed to build Trunk Recorder.

• Update the OS:

sudo apt update
sudo apt upgrade

• Add all of the libraries needed:

sudo apt -y install libssl-dev openssl curl git ffmpeg libcurl3-gnutls libcurl4 libcurl4-openssl-dev gnuradio gnuradio-dev gr-osmosdr libhackrf-dev libairspy-dev libairspyhf-dev libuhd-dev cmake make build-essential libboost-all-dev libusb-1.0-0-dev libsndfile1-dev

Configure RTL-SDRs to load correctly

wget https://raw.githubusercontent.com/osmocom/rtl-sdr/master/rtl-sdr.rules rtl-sdr.rules
sudo mv rtl-sdr.rules /etc/udev/rules.d/20.rtlsdr.rules

You will need to restart for the rules to take effect. Logging out and logging back in will not be enough.

sudo shutdown -r now

Configuring the UHD for Ettus SDRs (Optional)

You only need to do this step if you are going to be using an Ettus SDR

If you haven't setup UHD yet there are a few extra steps you need to take:

Install the UHD drivers:

sudo apt-get install libuhd-dev uhd-host

Download the firmware images. The location of the downloader is different than the error message:

dpkg -L uhd-host | grep "downloader"

Then run the downloader at the location identified, it should be something like this:

sudo python3 /usr/libexec/uhd/utils/uhd_images_downloader.py

Setup the udev rules so any user can access the USB, as documented here:

cd /usr/libexec/uhd/utils/
sudo cp uhd-usrp.rules /etc/udev/rules.d/
sudo udevadm control --reload-rules
sudo udevadm trigger

Building Trunk Recorder

In order to keep your copy of the Trunk Recorder source code free of build artifacts created by the build process, it is suggested to create a separate "out-of-tree" build directory. We will use trunk-build as our build directory. We by default do this in our home directory (~ - Is a shortcut back to home.).

Note: Depending on the amount of RAM in your Raspberry Pi, you may need to adjust the number of parallel compilation jobs to avoid running out of memory. If you run out of RAM, the compile process will fail completely, so it can be an acceptable tradeoff to use fewer parallel jobs. If it does fail, you can just restart the build from where it left off.

RAM Amount	Make Command	Notes
2GB or less	make -j1	Single-threaded compilation
4GB or less	make -j2	Two parallel jobs
8GB or more	make -j4	Four parallel jobs

cd ~
mkdir trunk-build
git clone https://github.com/TrunkRecorder/trunk-recorder.git
cd trunk-build
cmake ../trunk-recorder
make -j1
sudo make install

Configuring Trunk Recorder

The next step is to configure Trunk Recorder for the system you are trying to capture.

---

Ubuntu 22.04 Server (64-bit support!)

Ubuntu has a very good guide on setting up Ubuntu Server to run on a Raspberry Pi. Follow this to get started.

sudo apt update
sudo apt upgrade

sudo apt install -y apt-transport-https build-essential ca-certificates ffmpeg git gnupg gnuradio gnuradio-dev gr-osmosdr libboost-all-dev libcurl4-openssl-dev libgmp-dev libhackrf-dev liborc-0.4-dev libpthread-stubs0-dev libssl-dev libuhd-dev libusb-dev pkg-config software-properties-common cmake libsndfile1-dev

If you are using a HackRF:

sudo apt install -y hackrf libhackrf-dev libhackrf0

Configure RTL-SDRs to load correctly:

sudo wget https://raw.githubusercontent.com/osmocom/rtl-sdr/master/rtl-sdr.rules /etc/udev/rules.d/20.rtlsdr.rules

---

Building Trunk Recorder

In order to keep your copy of the Trunk Recorder source code free of build artifacts created by the build process, it is suggested to create a separate "out-of-tree" build directory. We will use trunk-build as our build directory.

Assuming you are in the desired directory to place both trunk-recorder and trunk-build folders to, perform the following...

cd ~
mkdir trunk-build
git clone https://github.com/TrunkRecorder/trunk-recorder.git
cd trunk-build
cmake ../trunk-recorder
make -j `nproc`
sudo make install

Note: If the Pi hangs during the make -j 'nproc' command, try make instead (it may take longer but may also prevent locking up the Pi due to all processor cores being 100% in use)

Profile

(It takes about 15 minutes for this section.)

Run the command volk_profile to ensure that VOLK (Vector-Optimized Library of Kernels) uses the best SIMD (Single instruction, multiple data) architecture for your processor.

Configuring Trunk Recorder

The next step is to configure Trunk Recorder for the system you are trying to capture.

Running trunk recorder

If all goes well you should now have the executable named trunk-recorder, and created the config.json configuration file as described in the Wiki and README.

From your build directory (e.g. trunk-build) you can now run ./trunk-recorder

Runtime options

Trunk Recorder will look for a config.json file in the same directory as it is being run in. You can point it to a different config file by using the --config argument on the command line, for example: ./trunk-recorder --config=examples/config-wmata-rtl.json.