Category: RTL-SDR

VMA Radio Lab: DecSAT Extended into a Multi-SDR Receiver with DVB-T/T2, DAB+ and Analog PAL TV

Last week we posted about DecSAT, an open-source program by CasualArclamp that turns a HackRF One into a DVB-S/S2/S2X satellite receiver and analyzer. Now Vitor Martins Augusto has written to share his fork, 'VMA Radio Lab' (initially called DecSAT-VMA), which extends DecSAT into a general-purpose broadcast receiver and measurement tool.

The biggest difference between DecSAT and VMA Radio Lab is multi-SDR operation. VMA Radio Lab can run several SDRs at once, each with its own VFOs, including the HackRF, PlutoSDR, USRP B210, RTL-SDR, SDRplay RSP1 and Airspy. One SDR can be dedicated to a sweeping wideband overview, such as the full 950 - 2150 MHz satellite IF. It also pulls in DVB-T/T2, DAB/DAB+ and TETRA decoding from CasualArclamp's sibling projects DecDVB-T, DecDAB and DecLAB, and adds analog radio, PAL color TV with teletext, measurement tools such as a vectorscope and transport stream analyzer, and control of CrazyScan-compatible TBS tuner cards for LNB power and hardware DVB reception.

Meanwhile, the original DecSAT remains satellite-focused. Since our last post it has added support for Fobos SDR, Airspy and network IQ input (including rtl_tcp), and has merged some of VMA's early RTL-SDR, PlutoSDR, B210 and analog TV code.

VMA Radio Lab is GPLv3 and available as a Windows 64-bit build and source zip on the website. We note that TETRA audio needs a separate ACELP codec DLL that isn't included for legal licensing reasons, and the bundled development notes describe several of the newer decoders, such as AIS and ACARS, as experimental. 

Decscat-VMA Screenshot
Decscat-VMA Screenshot

AI Disclaimer: The original DecSAT lists Claude as a contributor. While VMA does not disclose it, the development notes included with the VMA Radio Lab source suggest that its extensions were also written with the help of AI.

RS41 and M20 Android Decoder: A Standalone Radiosonde Decoder Android App for RTL-SDR

Back in June 2025, we posted about a radiosonde decoder and tracker program for Windows written by Mario Ančić (9A4AM). Mario has now written in again to share a new radiosonde decoder for Android, which works with an RTL-SDR dongle connected via a USB OTG adapter. As far as Mario is aware, it is the first standalone Android app dedicated to radiosonde decoding, as other solutions only offer it as an add-on within a larger SDR program.

The app decodes the common RS1729 radiosonde protocol and supports Vaisala RS41 and Meteomodem M20 sondes, with the type detected automatically, so you only need to enter the frequency and start decoding. As it is designed for radiosonde hunters, it skips PTU (pressure, temperature and humidity) data and focuses on position, altitude, speed, climb rate and heading. A 'Geo App' button passes the sonde's coordinates to your map app as a marker.

The decoder runs via the 'SDR driver' app by Signalware and was tested with our RTL-SDR Blog V3 and V4. The code is open source under the GPL-3.0 licence and available on GitHub, with the APK in the Releases section. Since the app runs as a background service, Android's battery optimization settings may need adjusting for it.

RS41 and M20 Android Decoder Screenshot
RS41 and M20 Android Decoder Screenshot

AI Disclaimer: The project README notes that parts of the code were written with the help of an AI assistant and reviewed by the author.

Frugal Radio: Testing the Discovery Dish on Inmarsat AERO with JAERO and InmarScope

Over on YouTube, Rob from the 'Frugal Radio' channel has uploaded part one of a review of our Discovery Dish, which we sent over for testing. Rob used the Inmarsat L-band feed with an RTL-SDR Blog V4, SDR++ and JAERO to receive AERO signals from the 98W satellite, which sits at about 27 degrees elevation from Rob's location in central Alberta.

Rob notes that the 10500 bps channels, which carry most aviation traffic and are usually the hardest to decode, held a steady Eb/No (a signal-to-noise measure for digital signals) of 14-16 over several days of testing. For comparison, Rob's previous best of 10 came from a grid dish designed for 1.7 GHz GOES reception, while our RTL-SDR Blog L-band patch antenna peaked at 8. Rob also shows the dish assembly, which took about 30 minutes.

Later in the video, Rob briefly tries out InmarScope, the multichannel Inmarsat decoder from Sarah Rose that we posted about previously. It decoded every 600, 1200 and 10500 bps AERO channel at once and automatically followed a voice call when one was assigned. Part two will cover maritime EGC, GOES reception, or more InmarScope, depending on viewer feedback.

Discovery Dish Review Pt 1 : High Gain Inmarsat AERO reception with SDR++, JAERO & Inmarscope

dec406: Decoding Second-Generation COSPAS-SARSAT 406 MHz Distress Beacons with an RTL-SDR

Thank you to Fabrice Morel (F4MLV) for writing in and sharing his project 'dec406', an open-source Linux decoder for COSPAS-SARSAT 406 MHz distress beacons. These are the EPIRBs carried on ships, ELTs on aircraft, and personal locator beacons (PLBs) carried by hikers. When activated, they transmit a digital message with a unique ID and often a GPS position, which satellites relay to rescue coordination centers.

What makes dec406 interesting is that it decodes the newer second-generation beacons. Unlike the narrowband first-generation signal, these use a ~50 kHz wide DSSS/OQPSK spread-spectrum signal that must be despread and BCH error-corrected before it can be read. Fabrice tested it with an RTL-SDR, and Bernard (F6BVP) at the F4KLO La Villette radio telescope used an Airspy on the MEOSAR satellite downlink near 1544 MHz, decoding system and calibration beacons in the USA, Cyprus, Brazil and Togo.

Fabrice has published real IQ recordings, and running 'make demo-real-sgb' downloads one and checks the decode. The live scanner supports RTL-SDR, Airspy, PlutoSDR, and HackRF, and the code is MIT licensed. More details are in the F4KLO field report. As Fabrice notes, never radiate test transmissions on 406 MHz. Fabrice has also sent us a PDF article of his results, which you can download here.

A Wide SGB Burst Near 406.05 MHz Received with an RTL-SDR in SDRangel (Top), dec406 Decoding a French Second-Generation System Beacon in Self-Test Mode (Bottom)
A Wide SGB Burst Near 406.05 MHz Received with an RTL-SDR in SDRangel (Top), dec406 Decoding a French Second-Generation System Beacon in Self-Test Mode (Bottom)

AI Disclaimer: While Fabrice does not mention it, the dec406 README and .gitignore reference a "Claude assistant memory" CLAUDE.md file, which suggests that Claude was used to help develop the software.

SimTX: A Multiplayer Shortwave Radio Simulator with Realistic Propagation and rtl_tcp Support

Recently, we came across SimTX, an open-beta multiplayer shortwave radio simulator. Everyone shares the same simulated band, so whatever one user transmits from their virtual station can be picked up by anyone else, simulated propagation permitting. The website suggests running a pirate station, making your own numbers station, or just tuning around and listening.

For realism, the ionosphere is based on IRI-2020 climatology with live ionosonde data assimilated on top, groundwave and noise follow ITU-R models, and every link passes through a Watterson fading channel with Doppler, multipath and storms. Users can transmit from a mic, an audio file or raw IQ from GNU Radio in modes including AM, SSB, CW, NFM, WFM, WSPR and FT8, and can even launch and track their own satellites.

To receive, the SimTX app runs a local rtl_tcp bridge, so SDR++ or any other rtl_tcp-capable SDR program can tune the simulated band as if it were an RTL-SDR, without any real radio hardware. The app runs on Windows, macOS, and Linux, and accounts are created via Discord. The software does not appear to be open source. The demo video below shows a song broadcast from a simulated Amsterdam and received 1145 km away in Budapest.

This may be useful for playing around with and seeing what different TX/RX variables and propagation effects do to signal reception.

We broadcast a song through a simulated ionosphere

Thermal Noise Communication: Sending Data Without a Carrier Signal, with an RTL-SDR as the Receiver

Thank you to RTL-SDR.COM reader Andrea for writing in and pointing us to a recent Stanford University press release about Zerina Kapetanovic and her team's research on "thermal noise communication", a way to send data wirelessly without generating any RF signal at all.

With this communication method, the transmitter simply switches its antenna between two loads, such as a dummy load and an open circuit, which the receiver sees as slightly "hotter" or "colder" thermal noise that encodes binary data. The study claims that a conventional RF transmitter uses up to 1,000 times more energy, making this a possible alternative to RFID tags and low-power wireless sensors.

Our reader Andrea also pointed out that the receiver in one of Zerina Kapetanovic's earlier experiments on the same topic was built around an RTL-SDR. Back in 2022, Zerina Kapetanovic and her team published a paper (pdf upload) demonstrating the idea at 1.42 GHz. Their receiver was a horn antenna, two LNAs with about 84 dB of combined gain, a bandpass filter, and an RTL-SDR, with processing on a laptop or Raspberry Pi. The transmitter was a simple RF switch connected to an antenna and switched between a 50 Ohm dummy load or ground. They achieved a data rate of up to 26 bps and a range of up to 7.3 m at 5 bps, and built a solar-powered, battery-free transmitter that sent indoor temperature readings over five days.

A new paper (not available freely yet) from Kapetanovic and her team builds on this idea and improves the data rate to the kilobit-per-second range, and adds capacity measurements and error correction, which was a limitation of their earlier experiment. The paper and press release also explain why this idea works at room temperature, making the analogy that the receiver's LNA works as a sort of 'electron refrigerator', slowing down electrons and making them appear colder.

We are unsure if the new setup still uses an RTL-SDR. However, readers who have built a Hydrogen line radio telescope have already built a nearly identical setup to the 2022 paper. In the press release Kapetanovic notes that "We've built a system that others could very easily implement", so this may be an interesting experiment to try for anyone who already has an H-line setup.

The thermal noise receiver setup from the 2022 paper
The thermal noise receiver setup from the 2022 paper

FalconSDR: An Open-Source RTL-SDR Scanner and Recorder with Automatic Whisper Transcription

Thank you to Rafał for writing in and sharing his open-source project FalconSDR, a free scanning and recording program he's been working on over the last few months. Rafał notes that after getting into RTL-SDR listening, he found that popular SDR programs didn't have the scanning and recording features he wanted.

FalconSDR can scan multiple bands or channels, even when they are far apart, with separate settings for each band and a blacklist for skipping birdies and unwanted channels. A "recency boost" feature sends the scanner back to channels with recent activity, and it can record multiple transmissions at once. Recordings go into a searchable library and can optionally be transcribed to text with Whisper. In hybrid mode, a server handles recording and a PC handles transcription.

The interface runs in a browser, either locally or on a headless server, so you can reach it from a PC or phone on your network. RTL-SDRs are supported natively, and Rafał has tested the program for months with an RTL-SDR Blog V4. Other SDRs work via SoapySDR. Linux and Windows 11 have been tested, but the macOS builds are marked as experimental. The code is open source under GPLv3 and available on GitHub.

FalconSDR Screenshots
FalconSDR Screenshots

AI Disclaimer: While the author does not disclose it, the repository includes an AGENTS.md file described as "Guidance for AI coding agents working in this repository", so it is our opinion that this software may be coded with the help of AI.

OrcSDR Update: SSTV, ACARS and Offline Maps Come to the Standalone ESP32-P4 RTL-SDR App

Back in September, we posted about OrcSDR, open-source firmware that runs an RTL-SDR directly on the ESP32-P4 microcontroller-based M5Stack Tab5 tablet, with no PC or Raspberry Pi needed. Erik Elfstrom has now written in again to share that OrcSDR v0.5.0-beta.1 (release notes) is out, with several new features and a lot of stability work.

The main additions are SSTV reception and a dedicated ACARS dashboard. SSTV images are drawn directly on the touchscreen and saved to the SD card, and the ACARS dashboard shows live messages and aircraft lists. Erik has tested SSTV with Robot36, PD120, and Scottie S1 on various RTL-SDR models. Offline maps have also been added to the LoRa/Meshtastic, ADS-B, and FT8 dashboards. There is also a new 'Dead Air' dashboard for logging RF and audio activity, and Erik notes that despite the Halloween timing, it is not a ghost detector.

Erik also notes that a lot of work has gone into fixing layout issues, redraw flicker and memory pressure, and there is now a guided first-run setup. The software is still in beta, and Erik says that not every issue is gone yet. The update can be installed with M5Burner or the browser installer, and the code is open source under AGPL-3.0 and available on GitHub.

Some screenshots of new OrcSDR Features
Some screenshots of new OrcSDR Features

AI Disclaimer: The OrcSDR README notes that the project was created with "extensive AI assistance".