Category: RTL-SDR

SDROxide: A New SDR Client for HAMs and SWLs written in Rust

Thank you to Josef (OE3JJS) for writing in and sharing with us the release of his new open-source software called SDROxide, an SDR client designed for HAMs and SWLs (short-wave listeners), written in Rust. The software supports Linux, Windows, macOS, and also has a web client. As it supports SoapySDR, RTL-SDR dongles are supported for RX. Josef writes about SDROxide:

It's a completely new project written in Rust, supporting many SDR interfaces (CAT/Audio, CAT/IQ, SoapySDR, HPSDR, TCI) and with loads of features built in that used to require extra programs: FT8/FT4, SSTV, RTTY, PSK, OLIVIA, THOR, FSQ, a CW/RTTY/PSK skimmer, there's dx cluster and sota/pota spotting, a logbook with integrations for QRZ.com, HamQTH, eQSL, LoTW, there's neural-network noise reduction, a 3D "hamclock" that visualizes QSOs, satellites, Aurora, CME cones, with up-to-date images of the sun's surface, and you can run the client locally, remote with native binary, or remote via the web (WASM).

Josef notes that the project is fully open-source and available on GitHub.

SDROxide: SSB Workspace
SDROxide: SSB Workspace
SDROxide: FT8 Workspace
SDROxide: FT8 Workspace

AI-Disclaimer: The author notes the use of local and hosted LLMs in the development of this software.

isTRAIN: Detecting if a Train is Blocking a Local Crossing By Listening to Railroad Frequencies

Jhestyr takes pride in being punctual, but a local railroad crossing keeps getting in the way. Trains sometimes park across it for hours at a time, and there is no way to know one is sitting there until you have already driven out to it. Every wasted trip to the crossing and back out to an alternative route costs him a significant chunk of time and fuel.

This is why Jhestyr used two RTL-SDR dongles to build isTrain, an open source program that decodes End-of-Train brake pressure and motion telemetry on 457.9375 and 452.9375 MHz, transcribes railroad voice traffic in the 160 to 162 MHz band via Whisper, and fuses both sources into a single live verdict on whether the crossing is blocked.

The program generates a webpage that can be accessed, providing a YES/NO verdict on whether there is a train blocking the crossing. A live public instance of Jhestyr's isTrain webpage is available here https://istrain.jhestyr.net.

AI-Disclaimer: Jhestyr notes that the code was developed with a 60/40 agentic/human split.

The isTrain Web Interface
The isTrain Web Interface

VibeSDR Now Available on the Apple App Store + Running on an Apple Watch

Back in June, we posted about VibeSDR, an AI vibecoded free and open-source mobile SDR client for rtl_tcp and UberSDR/KiwiSDR/OpenWebRX servers developed for iOS and Android. Recently, Stuart Carr (Stuey3D) wrote in again to let us know that VibeSDR is now available on the Apple App Store for £2.99 and is soon to be available on the Android Play Store too.

In terms of updates, Stuart also notes that he's now developed VibeServer, which provides a more network-efficient way to share RTL-SDRs remotely via an Android phone. VibeServer compresses the data and transfers it at 120KB/s instead of the full 4.8MB/s required by rtl_tcp. 

Stuart has also developed an Apple Watch Buddy app version of VibeSDR which runs directly on an Apple Watch, allowing you to view and listen to the spectrum on your wrist. The watch version is still in beta, but Stuart notes that you can join the free beta on TestFlight.

As before, the latest open source code can be found on the VibeSDR GitHub https://github.com/stuey3d/vibesdr.

Finally, Stuart has provided us with 20 free promo codes to give away for the Apple App Store version of VibeSDR. To win a promo code, simply comment on this post (making sure to enter an email in the email field), reply to the X post, or comment on the Facebook Post (note that for Facebook you must montior your comment for a reply as Facebook does not allow private messages). 

Update: All promo codes have now been allocated, thanks!

AI-Disclaimer: This software was vibecoded with Claude.

VibeSDR Running on an Apple Watch
VibeSDR Running on an Apple Watch
Introducing VibeSDR Jr: A full SDR Client on your wrist.

DeepSDR: Building a Live Public Safety Incident Map with an RTL-SDR, Whisper and an LLM

Over on Reddit and YouTube, user Hubquhq has shown how he created a live incident map using an RTL-SDR, Whisper and an LLM. The idea behind the system is to monitor multiple public safety voice communication channels with an RTL-SDR, transcribe everything into text using Whisper, and then use an LLM to categorize events and extract details such as addresses. Categorized incidents are then plotted on a map, allowing the user to visualize patterns. 

For example, in his YouTube video, he shows how he mapped cardiac, animal, drug overdose, vehicle collision, rescue, and hazmat events over time, building a powerful database of what is happening in his city.

The program and code does not seem to be available for download anywhere, but Hubquhq does provide a contact link for anyone interested. 

Systems that can monitor every RF voice and data channel on the spectrum and summarize them via an LLM are something we expect to see more of in the future as AI and LLMs improve.

Updates: Updated post with more information here.

DEEP SDR: How I Built an Incident Map

Exploring the Art and Science of Spectral Painting with SDR

Thank you to Paul Maine, who wrote in and wanted to share some experiments he and Gary Schafer have been doing with spectral painting. Spectral painting is the art of drawing pictures directly on the spectrum waterfall, which a software-defined radio makes visible. Paul has written the post below:

What happens when radio technology meets digital artwork? The result is something fascinating called Spectral Painting—the ability to create images that appear inside the radio frequency spectrum.

Gary Schafer (@signalgalaxiesunlimited) and Paul “The SDR Guy” Maine (@paulmaine6433) have teamed up to explore this unique combination of software-defined radio, signal processing, and creativity. Together, they have created companion videos on Spectral Painting and released them at the same time, each approaching the topic from a different perspective. For the best experience, it is recommended to watch Gary’s video first, followed by Paul’s practical demonstration.

Gary begins the journey by diving into the theory behind Spectral Painting. Using GNU Radio flowgraphs and GNU Octave scripts, he explains how images can be transformed into signals and displayed within the frequency spectrum.

Paul then takes Gary’s GNU Radio flowgraph and GNU Octave scripts from theory into practice. Using multiple SDR platforms, he demonstrates how to transmit spectral images using both the HackRF and TRX-DUO SDRs. He then completes the process by receiving and displaying the images using several different SDR receivers, including the RTL-SDR V3, RTL-SDR V4, and Airspy HF+.

Together, these videos provide a complete journey—from understanding the science behind Spectral Painting to seeing it come alive on real SDR hardware.

Below is an example screen capture of Spectral Painting in action.

Spectral Painting Example
Spectral Painting Example

Start with Gary’s video to learn the concepts and signal processing techniques:

Creating Spectral Paintings using Gnu Radio Companion (and other open source tools)

Then watch Paul’s video to see Spectral Painting transmitted and received using real SDR equipment:

E30 Spectral Painting

A Paper on Clock Distribution for Phase Coherent Operation of RTL-SDR Receivers

Modifying RTL-SDR dongles to run from the same clock source to create a phase-coherent receiver is something that has been done for many years. The original experiments from 2015 by Tatu Peltola and others are what inspired the creation of the KerberosSDR and KrakenSDR coherent RTL-SDR radio systems for radio direction finding.

Recently, Mykhailo Shumilov, an independent researcher in Ukraine, wrote a paper on running RTL-SDR dongles from the same clock, which may be of interest to those working on coherence experiments. In his experiments, he uses an Si5351A as the reference clock and two RTL-SDR dongles. While his paper doesn't cover any new ground, he presents concrete measurements confirming the phase coherence-stabilizing effect of running two RTL-SDR dongles from the same clock. 

AI-Disclaimer: The paper author notes that AI was used to aid in the writing of the paper.

Running two RTL-SDR dongles from a shared clock for phase coherence
Running two RTL-SDR dongles from a shared clock for phase coherence

Adding HD Radio Support to FM DX Webservers with an RTL-SDR

Thank you to Ivan (NO2CW) for submitting news about how he added HD Radio decoding capability to his FM DX Webserver receiver. The FM DX Webserver is a community of worldwide FM broadcast-band online receivers that mostly use SDRs based on the TEF6686 chip, with a few also using RTL-SDR receivers. HD Radio (aka nrsc5) is a proprietary digital audio standard used by FM broadcasters in North America. It's often observed by SDR users in a waterfall as the two rectangles flanking both sides of a broadcast FM signal. Ivan writes:

A major challenge has been that up until now none of the online receivers were HD Radio capable. I have now added this capability with the help of an RTL V3. The online receiver uses a combination of two receivers: a TEF6686 which is known to be highly sensitive and, when an FM HD Radio signal is present, an RTL V3 automatically kicks in to provide HD radio capability opening up HD1, HD etc audio streams together with bundled album art, traffic and weather. The program was initially conceived by discord user seehed and then further developed by me.

The core code for this plugin was developed by GitHub user seehed and can be found here: https://github.com/Seehed/NRSC5_HDRadio. I had to make a few tweaks to get it fully working.

How the Setup Works: The hardware setup requires both a TEF6686 receiver and an RTL dongle operating simultaneously.

I tested an RTL-SDR V4 first, but the necessary DLLs worked much better with an RTL-SDR V3 in my current build.

By default, the server uses the TEF6686 for browsing the FM band for analog signals. When a user tunes to a frequency where an HD Radio signal is present, the logic switches to "HD Mode" and the RTL V3 takes over. The NRSC5 library is used to process the digital signal. In this mode, users will notice the change in audio quality and the available subcarrier streams (HD1, HD2, HD3, etc.) become visible and selectable.

How Users Can Set It Up: To replicate this, a user would need:

  • A working FM DX Webserver with a TEF6686.
  • An RTL-SDR V3 plugged into the same host.
  • The NRSC5 library installed.
  • The plugin from the GitHub link above installed and configured in the webserver directory.

Ivan also notes that currently his Miami NO2CW receiver is the only one on the network supporting HD Radio.

HD Radio on FM DX Webserver. Receiving HD Radio inside the fm dx webserver application.

HD Radio Added to FM DX Webservers via an RTL-SDR
HD Radio Added to FM DX Webservers via an RTL-SDR

Demod: An iOS/iPadOS Client for rtl_tcp, SpyServer and KiwiSDR

Thank you to Alphonse Romero for submitting news about the release of his new iOS and iPadOS SDR receiver app called Demod. Demod is a network client that connects to remote SDR servers, so it can be tried out immediately with no dongle needed at all. 

The app works as a client for rtl_tcp, SpyServer (Airspy and RTL-SDR), and KiwiSDR, all in a single app. It features a Metal-accelerated waterfall and spectrum display, AM/NFM/WFM/USB/LSB/CW demodulation, and adjustable bandwidth, gain, and squelch. Other features include frequency memories with CSV import and export, AirPlay and Lock Screen controls, and native layouts for both iPhone and iPad. It can also browse and connect to public SpyServers directly from within the app, which is how it can be used with no hardware of your own. The developer notes that it collects no data, with no ads or tracking.

Alphose writes that Demod is a solo project and is available on the US App Store for US$9.99. More information and screenshots can be found on the project website, and the app itself is available on the App Store.

The developer has also provided us with 15 free codes that we will be giving away in one week. To enter the giveaway, simply comment on this post (make sure to include your email address in the comment so that we can send you the code), the X post, or the Facebook post. (UPDATE: ALL CODES HAVE BEEN ALLOCATED NOW, THANKS!)

Demod iOS SDR App
Demod iOS SDR App