Category: Applications

GNU Radio World: Browser-Based GNU Radio Flowgraphs

Thank you to Marc Lictman, vice president of GNU Radio, for writing in and sharing with us his new project called "GNU Radio World," which is essentially GNU Radio Companion in a web browser, written in WebAssembly.

If you're not familiar with it, GNU Radio is a very popular free and open-source toolkit for implementing digital signal processing algorithms and applications. It lets you experiment with and build radio receivers, transmitters, and DSP chains through a graphical block-based flowgraph.

Marc Lictman writes:

I thought your readers might be interested in the relatively new website that I put together, https://gnuradioworld.com, as it is starting to have some nice RTL-SDR support, e.g. there is a basic spectrum analyzer and a full ADS-B application with map, but the best part is that it's really just GNU Radio in the browser so you can assemble your own flowgraphs and play around without installing anything, either with live USB SDRs, signal recordings, or simulated signals. It runs entirely client-side and comes with several out-of-free modules (OOTs), including gr-adsb by Matt Hostetter.

The other nice part about GNU Radio World is it comes with dozens of example flowgraphs (see tab on the left) as well as a bunch of example IQ recordings that can be used in place of the typical File Source block, and when you run the flowgraph it streams the IQ to your browser, a lot of the IQ recordings are used in the example flowgraphs to show off various OOTs functionality.

The whole project is free and open source (GPLv3), I think that it will be especially valuable for those learning RF signal processing, and those without a Linux background who want to jump straight into learning GNU Radio. Here are some specific example flowgraphs that may be of interest to RTL-SDR enthusiasts:

If anyone wants to reach out, they can email [email protected] or join the Discord server linked at the top of the site.

We test-drove GNU Radio World with both RTL-SDR Blog V3 and V4 dongles and found it to work well. However, it seems that V4L support has not been added yet. We have forwarded this feedback to Marc, so hopefully it will be supported soon.

GNU Radio World Browser Flow Graph
GNU Radio World Browser Flow Graph
GNU Radio World Running an RTL-SDR Blog V3
GNU Radio World: Running an RTL-SDR Blog V3

GridDown Secure Messenger: Using an SX1262 LoRa Radio as a Drone Scanner and Secure Messenger

Back in March, we posted about GridDown, an open-source Android tablet-based situational awareness system designed to operate without an internet connection, which uses sensors such as an RTL-SDR, a SARSAT receiver and an ESP32-S3/SX1262 LoRa radio.

Recently, GridDown developer Cameron wrote in again and shared with us that the LoRa firmware for GridDown has now been released as an open-source project called "GridDown Secure Messenger" (main website).

The project uses a LILYGO T-Deck CYPHER-M8K (an ESP32-S3 with SX1262, 2.8" display, keyboard, and GPS) to implement secure, encrypted off-grid text messaging, and it also doubles as a 900 MHz drone scanner, with the ability to decode drone Remote ID.

Cameron has also provided two YouTube shorts [1] [2], showing the firmware in action.

Example Renders of the GridDown Secure Messenger Running on a LILYGO T-Deck CYPHER-M8K.
Example Renders of the GridDown Secure Messenger Running on a LILYGO T-Deck CYPHER-M8K.

AI Disclaimer: The renders appear to have been AI-generated.

IC-SDR: A New Multimode SDR Software for Windows Written in Go

Thank you to Luis Lopez Martinez for writing in and sharing the release of his open-source software, IC-SDR, a new multi-mode SDR application for Windows written in Gowith a focus on performance and efficiency. Luis writes:

IC-SDR supports AM, NFM, WFM, LSB and USB demodulation, along with several integrated digital decoders:

  • AIS
  • ADS-B (1090 MHz and UAT 978 MHz)
  • Radiosondes
  • APRS
  • RTL_433
  • DMR
  • SSTV
  • TETRA

It also includes a memory bank, real-time spectrum and waterfall displays, an audio recorder with automatic silence removal, and a frequency-segment scanner with instant triggering.

The Windows release can be found on the project's GitHub Releases page.

Instro: Python Hardware Instrumentation Library Adds RTL-SDR Support

Instro is an open-source Python library designed to talk to test instrumentation such as power supplies, multimeters, electronic loads, DAQs, oscilloscopes, and PLCs from a unified, typed API.  The maintainers describe the goal as follows:  "Code against an instrument category once, then swap vendors with a single configuration change. When you want to capture the data, attach a publisher to stream it to a file, Nominal, or a destination of your own." A library like this saves engineers from having to write custom drivers for each piece of equipment.

Recently, Alexander Arsenovic, the original author of the excellent scikit-rf RF engineering Python library, wrote and wanted to share that he has added RTL-SDR support to Instro. He has uploaded a video showing it in action with an RTL-SDR Blog V3.

The code is open-source and available on GitHub.

rtl-sdr in nominal.instro

SDR++ IAK: A Modified Version of SDR++ Available on the Google Play Store

SDR++ is a popular general-purpose SDR receiver program, commonly used by RTL-SDR enthusiasts. It works on all platforms, including Android; however, the original author has not expressed interest in officially publishing it on the Google Play Store, so sideloading the APK has been the only way to get it on Android.

Recently, we've learned of an unofficial SDR++ fork called "SDR++ iak" that is now on the Google Play Store. The iak fork by OK1IAK includes several improvements, notably a touch-friendly UI overhaul, various crash fixes, KiwiSDR world-map directory, radiosonde decoder, and support for the QRP Labs QMX transceiver.

SDR++ IAK Screenshots
SDR++ IAK Screenshots

An HTML Browser Page that Uses Display Pixel Clock EMI Leakage to Transmit VHF Morse Code

Thank you to Efe (TA1EEI) for writing in and sharing an HTML web tool he created that uses a PC monitor to transmit Morse code. The tool works by modulating the monitor's pixel clocks to intentionally generate EMI leakage in the form of a Morse code signal. It transmits at 148.5 MHz.

Efe's work appears to be a much simpler version of TrojPix, a University research project that we posted about back in July. TrojPix is a more advanced system that introduces imperceptible pixel modulations into the screen, making high-bandwidth wireless data transfer possible via monitor EMI leakage.

The GitHub project page for Efe's VHF Monitor RF Transmitter explains exactly how the project works, including the video pixel clock and how it can be modulated and transmitted wirelessly. Efe has also provided a link to a Reddit post where there is a video, and discussion. 

VHF Morse Code Transmitted via an HTML Page
VHF Morse Code Transmitted via an HTML Page

VibeSDR Jr: Apple Watch RTL-SDR, KiwiSDR, UberSDR Client now Available

Back in July, we posted about VibeSDR, an AI vibecoded open-source mobile SDR client for rtl_tcp and UberSDR/KiwiSDR/OpenWebRX servers developed for iOS and Android. In that post, Stuart also mentioned that he was developing an Apple Watch app version of VibeSDR that runs directly on an Apple Watch, allowing you to view and listen to the spectrum on your wrist.

The Apple Watch version, called VibeSDR Jr, is now available as a full standalone Apple Watch App, meaning that no iPhone is required. The app costs £0.99 (~US$1.35). As before, Stuart has provided us with 20 free giveaway codes for the VibeSDR Jr App, so be sure to comment on either this post, the Facebook post, or the X post for a chance to win one of the codes.

Stuart has also noted that he now has a live VibeSDR demo running at demo.vibesdr.net, allowing users to see VibeSDR's DSP and server functionality in action. Stuart writes, "There is an RTL-SDR V4C, SDRPlay RSP1B, and AirSpy HF running on that demo server, all connected to the same AirSpy YouLoop with LNA antenna setup. The RSP1B is locked to 2.8MHz - 10.8MHz and can handle 10 users and the RTL-SDR & AirSpy are unlocked frequencies but 1 user at a time, each user gets a 30 minute time slot to play with. All the built in decoders are available and for the FM-DXers there is a full advanced RDS suite measured against a professional broadcast analyser too."

He also notes the following to avoid confusion with the software in the VibeSDR family:

VibeSDR + Buddy: The Main VibeSDR app and the Apple Watch Remote control companion app for that app.
VIbeSDR Jr: The full standalone Apple Watch SDR client no iPhone required
VibeServer: Built in to Android and standalone apps which allow you to quickly and easily share your SDR’s on a network

Use VibeServer to connect your radio and serve it and then use Jr to listen to it on your wrist, or if you don’t have your own radio Jr is compatible with almost all the same servers as the main VibeSDR app, the only thing it cannot do due to bandwidth/processing requirements is anything that is RAW IQ such as RTL-TCP or SpyServer.

Finally, Stuart notes that the Android version is coming soon and is currently just pending acceptance on the Google Play Store.

VibeSDR Jr - SDR Client for the Apple Watch
VibeSDR Jr - SDR Client for the Apple Watch

Carshepherd: An Android RTL-SDR App For the Early Awareness of Nearby Emergency-Service Vehicles

Thank you to Cees for writing in and sharing his Android app, "Carshepherd," which is currently in the pre-release stage. Carshepherd works with a connected RTL-SDR and TETRA antenna to give drivers early awareness of nearby emergency-service activity (such as police, ambulance, fire) by detecting the TETRA uplink signal.

Cees notes that this is essentially the same as what hardware devices like 'Target Blu Eye' do to detect emergency services. Laser/radar detectors are illegal in most European countries, and while not advertised as such for legal reasons, Carshepherd could be a legal alternative for detecting laser/radar speed traps, detecting ProViDa video-based pacing vehicles, or just for general awareness.

The app works by continuously sweeping the TETRA bands, looking for the signature of a TETRA carrier. Once it detects a confirmed uplink carrier, it estimates proximity, which then triggers a readout and audible alert. The TETRA uplink is not always active, but emergency service vehicles often send bursts of uplink data every few seconds with GPS position updates, and, of course, during voice PTT.

The algorithm is based on a large labeled dataset from dozens of real-world test drives. The dataset trains an AI classifier that can even tell you whether an emergency unit is keeping pace with you (e.g., traveling down the same stretch of motorway as you) or whether you are approaching a stationary unit.

Carshepherd currently only works in countries whose emergency services use the TETRA communications protocol, which includes most of Europe and various other countries, but notably not the USA. However, Cees notes that they are working on a US version that will listen to the P25 network.

While Carshepherd has not yet been released, the pricing is indicated as €3.99 per month. You can sign up for the waitlist at www.carshepherd.nl.

Sept 5 2026 Update: Carshepherd is now live on the Google Play Store.

Carshepherd Android UI
Carshepherd Android UI