Building a Receive-Only APRS iGate with Raspberry Pi and SDR

624 words, 3 minutes read time.

In the world of amateur radio, APRS (Automatic Packet Reporting System) offers a fascinating glimpse into real-time data transmission, ranging from location reports to weather updates. For those interested in receiving APRS data without transmitting, building a receive-only APRS iGate is a rewarding project. In this blog, we’ll walk through creating a receive-only APRS iGate using a Raspberry Pi, an SDR receiver, and a few essential components. This project allows you to capture APRS packets and forward them to the internet, contributing to the broader APRS network. Let’s dive into the process!

What You’ll Need

To start, you’ll need a few key components:

1. Raspberry Pi with Headers: This is the heart of your project, running the software and processing the APRS data.
2. USB Adapter Cable: For connecting the SDR receiver to the Raspberry Pi.
3. RTL-SDR Receiver: A software-defined radio (SDR) that captures the APRS frequencies.
4. Antenna: To receive the APRS signals effectively.
5. Display: A small screen to show the APRS data.

Preparing Your Raspberry Pi

1. Install Raspberry Pi OS: Download and install Raspberry Pi OS onto your SD card. You can use the official Raspberry Pi Imager for this purpose. Ensure that the OS is up-to-date by running:

sudo apt-get update

Install Required Software: Open a terminal and execute the following commands to install necessary packages and software:

sudo apt-get install direwolf rtl-sdr git python3-pip fonts-dejavu python3-pil python3-pyinotify python3-numpy
sudo pip3 install --break-system-packages adafruit-circuitpython-rgb-display
sudo pip3 install --break-system-packages aprslib

Enable SPI Interface: Edit the Raspberry Pi configuration file to enable SPI, which is necessary for the display and communication with the SDR. Open the configuration file with:

sudo vi /boot/firmware/config.txt

Find the line that starts with #dtparam=spi=on and uncomment it by removing the #. It should look like this:

dtparam=spi=on

Save and exit the file by pressing CTRL+X, then Y, and Enter. Reboot the Raspberry Pi to apply the changes:

sudo reboot

Setting Up the APRS Software

1. Clone the Direwatch Repository: Direwatch is a tool that will help you visualize the APRS data on your display. Clone the repository from GitHub using:

git clone https://github.com/craigerl/direwatch.git

Configure Direwolf: Direwolf is a software TNC (Terminal Node Controller) that decodes APRS packets. Create and edit the Direwolf configuration file with:

sudo vi /etc/direwolf.conf

Add the following configuration, replacing NOCALL with your callsign (if you have one) and providing a valid login for APRS-IS:

MYCALL NOCALL
IGSERVER noam.aprs2.net
IGLOGIN NOCALL 12345
PBEACON sendto=IG compress=1 delay=00:15 every=30:00 symbol="igate" overlay=X lat=40.911 long=-122.935 comment="Direwatch Rx-only igate"
AGWPORT 8000
KISSPORT 8001
ADEVICE null

Start Receiving and Displaying APRS Data: With the hardware set up and software configured, you’re ready to start capturing APRS packets. Connect the SDR receiver to your Raspberry Pi and attach the antenna. Then run the following commands to start the process:

rtl_fm -s 22050 -g 49 -f 144.39M 2> /dev/null | direwolf -t 0 -r 22050 - > direwolf.log &

./direwatch.py -o -l direwolf.log -t "APRS"

1. These commands will start the SDR receiver, feed the data into Direwolf, and display the APRS information on your screen.

Additional Notes

• Display Configuration: Ensure that the display is correctly connected and configured. If you encounter issues, check the connections and refer to the display’s documentation.
• Older Raspberry Pi Models: For older models of Raspberry Pi, you might need to build Direwolf from the source rather than using the precompiled package.

Resources

For additional support and updates, you can visit the Direwatch GitHub repository. Special thanks to Hessu for providing the SVG APRS symbols used in this project.

By following these steps, you’ll have a functional receive-only APRS iGate up and running in no time. This project is a great way to dive into the world of APRS and contribute to the amateur radio community. Enjoy your new APRS receiver and the insights it provides!