Tagged: raspberry pi

A Homemade Boat Computer with RTL-SDR for Weather Fax, NavTex and more

Over on Hackaday we've seen a post about [mgrouch]'s "boat computer" which consists of a Raspberry Pi 4, HDMI display, and a whole slew of sensors and receivers useful for a marine environment including an RTL-SDR.

The built in equipment includes a GNSS receiver, orientation sensors, AIS receiver, 4G and WiFi, lightning EMI sensor and alarm, optional autopilot integration, rudder angle sensor, connections to boat instruments like wind, depth, speed, temperature, barometric and humidity sensors, an Iridium receiver, and finally an RTL-SDR for receiving weather fax, NavTex, satellite weather, AIS, RTL 433, morse code and more. It really is an "all-in-one" device.

His blog post explains in detail how each of the components work in the system, and in particular for the RTL-SDR he shows how you can use the boat computer to receive FM via GQRX, and NavTex via the Java based Frisnit Navtex decoder. Navtex is a marine radio service that transmits at 518 kHz or 490 kHz. It provides text data regarding weather forecasts, weather warnings, navigational information, and urgent maritime safety messages. For his antenna he writes that he uses a 10 kHz - 30 MHz Mini Whip antenna that he purchased on Aliexpress.

mgrouch's Boat Computer with RTL-SDR
mgrouch's Boat Computer with RTL-SDR

Remote Spectrum Monitoring with OpenWebRX, RTL-SDR and the Balena Cloud Service

Thanks to Alan Boris of Balena.io for submitting their new blog post titled "Running OpenWebRX on balena to remotely monitor local radio spectrum". Balena.io is an IoT cloud service that is used for "building, deploying, and managing fleets of connected Linux devices".

In the blog post, they show how it's possible to use a RTL-SDR and Raspberry Pi running OpenWebRX to remotely monitor the radio spectrum over the internet. This of course has been done many times before, however, the novel thing here is the use of the Balena cloud platform which makes installing and managing the Raspberry Pi running OpenWebRX much easier.

Balena has a has a special balenaOS image that is first burned on the Raspberry Pi's SD card. The OS image is pre-generated with your home WiFi details, so upon boot it automatically connects to the internet and can be accessed on the balenaCloud dashboard. At that point you can easily remotely push the pre-made Balena "sdr-spectrum-monitor" docker image to the Pi from the Balena online dashboard. This docker image has OpenWebRX and the RTL-SDR drivers already installed on it. It's then a simple matter of connecting to OpenWebRX via the local IP address as you would normally.

This is quite a nice system as it avoids needing to perform the "fiddly" steps of setting up WiFi, connecting to the Pi, determining the Pi's IP address, and installing the RTL-SDR drivers and OpenWebRX software manually.

Balena also has a very simple way to make the OpenWebRX server accessible from outside your network. The only steps required are to set a port variable in the Balena cloud dashboard, and enable the "public device URL" option. No need to fiddle around with unblocking ports or dynamic DNS services.

Balena.io appears to be free for personal use, allowing you to add and manage up to 10 devices before needing to pay.

RTL-SDR & OpenWebRX Installed and Managed via Balena Cloud.
RTL-SDR & OpenWebRX Installed and Managed via Balena Cloud.

PyPacket: An APRS iGate For Your RTL-SDR

[Pypacket] was developed by GitHub user [cceremuga] and allows you to take advantage of a Linux computer (such as a Raspberry Pi) and an RTL-SDR to quickly and easily build your own APRS iGate.

For those not familiar with APRS, it stands for the [Automatic Packet Reporting System] and is used by amateur radio operators for applications like transferring messages and location data over RF networks and the internet. The internet connection is where an iGate comes into play. An iGate is used to connect an APRS RF network to the internet, so that many isolated RF APRS networks can communicate worldwide. Furthermore this software can be configured as a “SatGate”, which like an APRS iGate will take messages from APRS satellite’s and route them over the internet.

For example, you could have an amateur radio vehicle continually transmitting it’s location via RF to an APRS iGate. The vehicles position can then be viewed online on an APRS aggregation site like aprs.fi, or it could be re-transmitted over RF elsewhere in the world.

An iGate is usually accomplished by using a ham radio tuned to the local APRS frequency (or sat frequency) and then special PC software is configured to gate the messages.  However, with the release of PyPacket the amount of work and cost required to setup an iGate has been cut drastically. 

Raspberry Pi 4 Released: Improvements to CPU, Networking, USB, RAM and more

The Raspberry Pi is the most popular credit sized computing board in the world. It is commonly used as a low cost and portable computing platform for SDRs like the RTL-SDR. Today the Raspberry Pi 4 was released, bringing us a new US$35 single board computer with many improvements. Some of the main improvements that make the Pi 4 great for software defined radios are listed below:

CPU: The Pi 4 uses a Quad-Core Broadcom ARM A72 clocked at 1.5 GHz. This chip should be significantly faster compared to the older chip used on the Pi3B+ with performance now being similar to that of the Tinkerboard. This will be especially useful for CPU intensive SDR applications like the direction finding and passive radar software for our coherent 4-tuner RTL-SDR known as the KerberosSDR. It should also help allow OpenWebRX servers to serve more simultaneous users, allow graphical programs like GQRX to run smoother, and allow for higher sample rates on higher end SDRs.

GPU: The new faster GPU should help graphical SDR programs run smoother.

RAM: The Pi 4 comes with three RAM options, either 1GB, 2GB or 4GB of RAM. The versions with more RAM will be great for memory intensive applications such as GNU Radio (and compiling GNU Radio). It will also allow more programs to run in the background, and perhaps combined with the improved CPU speed allow for multiple SDRs to be used on demanding tasks.

Networking: The Pi 4 finally support Gigabit Ethernet which will be very useful to people using the board as an SDR server over the internet.

USB: There are now two USB 3.0 ports available which means that USB 3.0 SDRs like the LimeSDR could in theory be used at higher sample rates on the Pi 4.

There are also many other improvements such as dual 4K HDMI ports, a USB-C power supply port and faster SD card transfers.

Raspberry Pi 4 Improvements
Raspberry Pi 4 Improvements

It is not yet known if the very useful Raspberry Pi specific software known as RPiTX will continue to function on the new Pi 4. RPiTX is software that turns Raspberry Pi units into fully functional RF transmitters without the need for any additional transmitting hardware - just attach an antenna wire to a GPIO pin. It works by modulating the GPIO pin in such a way to create almost any type of RF transmission. RPiTX only functions on the specific proprietary Broadcom CPU chips that the Raspberry Pi's use. The Pi 4 does continue to use a Broadcom CPU, so we are hopeful.

The new changes bring the Raspberry Pi up to speed with rivals like the Tinkerboard, but at a lower price and with a much better amount of software and OS support provided. The boards currently cost $35 for the 1GB version, $45 for the 2GB version and $55 for the 4GB version. They are sold via local resellers which can be found on the official Pi 4 product page.

An RTL-SDR and Pi 3 Based Ground Station for Simulated CubeSats

CubeSats are small and light satellites that can these days be built and launched into orbit by almost anyone with a small budget of roughly $40,000. They are a great way for schools and other organizations to get into a space based technology project. A "simulated" CubeSat is one that is not designed to be really launched into space, and is made from low cost hardware. The idea is that simulated CubeSats can be used as tools to help demystify the inner workings of satellites to the public and help CubeSat builders get experience and competence before building the real thing.

A Simulated CubeSat made from a Solar Panel board, Pi Zero, UPS and Tranceiver.
A Simulated CubeSat made from a Solar Panel board, Pi Zero, UPS and Transceiver.

A team from AMSAT have been working on creating open source CubeSat simulator hardware and software. In order to demonstrate the RF capabilities of the simulator a ground station simulator is also required. Recently the team have uploaded instructions on creating a Raspberry Pi and RTL-SDR based ground station.

If you're interested in the CubeSat simulator hardware itself, there was a presentation held back in 2018 that may be of interest to you. According to the presentation somewhere between 30% - 50% of CubeSats fail as soon as they're deployed, so building competence with simulated hardware is a good goal.

2018 AMSAT William A. Tynan W3XO Memorial Space Symposium - Saturday Sessions

A Raspberry Pi and RTL-SDR Based Boombox

Thank you to Walter P. for writing in and sharing with us his conversion of an old analog boombox into a fully functional wideband software defined radio based on an RTL-SDR dongle and upconverter.

Walters Ghettoblaster RTL-SDR Radio
Walters Boombox RTL-SDR Radio

Inside the boombox Walter stripped away the analog circuitry and replaced it with a new LCD screen, Raspberry Pi, RTL-SDR, upconverter and an audio amplifier. Four rotary switches on top of the radio are used to control the frequency, demod mode and volume, and there is also a numerical keypad which can be used to enter the frequency directly. 5V and HF antenna connectors have been added to the side, as well as an upconverter enable switch on top. Walter also added a Spyserver mode to the software, which allows you to connect to the radio over WiFi with SDR#, although he notes that using the integrated Pi WiFi module seems to introduce noise on the speakers.

If you're interested in building a similar device, Walter has provided the full Python code and installation instructions for his build.

Edit 09 May 19: It was pointed out that the word "ghettoblaster" could be considered offensive in some cultures. We have changed the word in our article to "boombox" and apologize for any unintended offence.

RaspBRadio - ghettoblaster with sdr radio scanner inside

Reaching Across Europe with a Raspberry Pi Zero and WsprryPi

Over on YouTube user Techminds has uploaded a video that shows how he is using a Raspberry Pi Zero to transmit WSPR. To do this he uses the WsprryPi software which allows you to transmit WSPR by connecting an antenna directly to a GPIO pin on the Pi Zero. With this no extra hardware is required, although a filter is highly recommended to reduce spurious emissions from harmonics.

In his test Tech Minds directly connected the Pi Zero to an unun and HF wire antenna and ran WsprryPi. His results showed that even with the tiny 10mW output power of the Pi Zero's GPIO port his WSPR messages were able to reach several receivers halfway across Europe, and even to Iceland and Morocco from his home in the UK.

WSPR is an amateur radio digital HF mode designed to be decodable even if the signal is transmitted with very low power and is very weak. It can be used to help determine HF radio propagation conditions as WSPR reception reports are typically automatically uploaded to wsprnet.

WSPR - Weak Signal Propagation Reporter - From A Pi Zero ?

A Portable RTL-SDR Based ADS-B Receiver with Display and 3D Printed Enclosure

Over on Hackaday.io user nathan.matsuda has written about his RTL-SDR based hand held ADS-B aircraft receiver with display and 3D printed enclosure.

His initial idea was to create a flexible and open portable SDR device, however keeping the device open and built for general use meant increased complexity which quickly slowed his progress. Instead [Nathan] decided to focus on just ADS-B for his portable device as living near an airport he’d been interested in aircraft tracking since his first SDR arrived.

The device consists of a Raspberry Zero, RTL-SDR, 3.5″ IPS LCD and a battery pack for portability. For software he uses dump1090 with some custom code for the map plotting. Together with a 3D printed case and some buttons, the result is a very professional looking portable aircraft tracking device.

Hopefully Nathan will continue updating his project page so that others may replicate it on their own.

Raspberry Pi Zero and RTL-SDR Portable ADS-B Receiver
Raspberry Pi Zero and RTL-SDR Portable ADS-B Receiver