Category: Amateur Radio

Clever Quest Lab: Free Browser-Based Decoders for RTTY, Weather Fax, SSTV, NAVTEX, APRS and More

Thank you to Simpli for writing in and sharing a set of free radio decoders that run entirely in the browser. There are pages for Morse, RTTY, PSK31, SSTV, weather fax, NAVTEX, APRS and the DCF77/MSF time signals, plus a signal identifier that tries to name an unknown mode and links to the matching decoder.

Audio can come from your SDR program via a virtual audio cable, a microphone, a WAV or MP3 recording, or a WebSDR playing in another browser tab (this needs a desktop browser with screen sharing), so no hardware is needed to try them. Simpli tested them on DWD RTTY on 4583 kHz and DWD weather fax on 3855 kHz via the Twente WebSDR, as well as on live PSK31 and an ISS SSTV recording in PD120 mode.

Simpli writes:

A detail you might find interesting: the WebSDR player inserts 128 zero samples about once a second, and its playback speed wanders by up to half a percent. That's enough to tear a fax picture apart. The fax decoder cuts those gaps out and tracks the speed from the white tone, so the chart comes out straight. The RTTY page also switches to reversed polarity by itself when it sees too many framing errors.

All decoding happens locally with nothing uploaded, and the tools are free with no sign-up. This is similar in spirit to OFFgrid-SDR, which we just posted about, as both run in the browser and can automatically identify a mode. However, OFFgrid-SDR connects directly to an RTL-SDR via WebUSB and is open source under the GPLv3, while Clever Quest Lab's decoders work on audio from any receiver and do not appear to be open source.

Clever Quest Web Browser Weather Fax Decoder
Clever Quest Web Browser Weather Fax Decoder

ESPica32: A Standalone ESP32 Radio for Tuning Any KiwiSDR with No PC or Phone

Thank you to Ivan (LU8MIL) from the ‘Radio Bunker’ YouTube channel for writing in and sharing ESPica32, a standalone ESP32-based radio that tunes into any public KiwiSDR in the world with no PC or phone needed. The name is a tribute to the Spica, a pocket transistor radio that was hugely popular in Argentina.

The build uses just four parts: an ESP32-WROOM-32, an SH1106 OLED display, a rotary encoder, and a MAX98357A I2S amplifier with a small speaker. A single encoder controls frequency, volume and mode (LSB, USB, AM, CW and FM). A web page served by the ESP32 handles Wi-Fi setup, KiwiSDR server selection and full remote control, and also includes a diagnostic for tracking down audio dropouts.

Ivan notes that distant KiwiSDRs initially cut out because the ESP32 couldn’t keep up with uncompressed audio. Switching to the KiwiSDR’s ADPCM compression fixed this, and a Kiwi in Argentina now plays cleanly from Germany at about 260 ms ping. The Arduino IDE sketch and wiring diagram are available on Ivan’s Todo-SDR blog, and the Spanish-language video below shows the build and a demo (English subtitles are available).

🎯 EL PROYECTO DIY QUE TODO RADIOESCUCHA DEBERÍA CONOCER: ESPica32

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

OrbitNight: A Free Browser-Based Satellite Pass Viewer with Antenna Rotator Control via Web Serial

Thank you to the OrbitNight team for writing in and sharing their "OrbitNight satellite radar", a free browser-based pass viewer for any satellite in the catalog. It can also point an antenna rotator straight from the browser over USB using Web Serial, so you don't need to install anything.

The radar page shows a polar plot of the pass track, live azimuth and elevation readouts, and an AOS/LOS countdown. A radio tab lists downlink and uplink frequencies taken from SatNOGS. For rotator control, it supports Yaesu GS-232 compatible controllers (including K3NG and ERC) and EasyComm II controllers like those used on SatNOGS stations connected over USB serial, or Bluetooth on Android. It also has an azimuth offset setting and a 1 degree deadband.

The site works in Chrome and Edge on desktop, and rotator control needs a browser that supports Web Serial. It's free and needs no sign-up. The team notes that there is no 450 degree or flip mode yet, and they'd like to hear from anyone who tries it with a real rotator. If you track LEO satellites with a directional antenna and an RTL-SDR, this could be a simpler option than setting up Gpredict and Hamlib. We note, however, that we couldn't find an open-source codebase.

The OrbitNight Live Tracking Page
The OrbitNight Live Tracking Page

Muxwright: A Multi-Standard Radio and TV Test Transmitter for the PlutoSDR

Thank you to Peter Holzhauser for writing in and sharing Muxwright, a multi-standard radio and TV test transmitter for the ADALM-Pluto (PlutoSDR). Peter has in the past submitted his ESPSoup, and Etherbulb projects. Muxwright is intended for home lab testing only, with the Pluto connected to the receiver under test via cable and attenuator or inside a shielded box, as radiating broadcast standards over the air requires a frequency assignment.

Muxwright can generate FM stereo with RDS/RBDS, DAB+, DVB-T, DVB-T2, DVB-C, DVB-S/S2, ATSC 1.0, ISDB-T, DTMB and analog PAL/NTSC TV, plus DVB-S2 DATV for QO-100 and other amateur bands (which of course requires an amateur radio license). The digital TV modulators run directly on the Pluto and everything is controlled from a browser dashboard. The Pluto's RX input can also be used as a monitoring receiver for expected vs. actual test reports.

The software runs on Windows 10/11 via WSL2 and is currently at Beta 0.4. The README notes that it has only been verified on the original Pluto Rev. B, and that DVB-T2, ATSC, ISDB-T and DTMB are still untested with real TV sets. The code is MIT licensed (with the FM/RDS module under GPL-3.0) and available on GitHub, however, the Windows installer is only available by request via email from the website.

Muxwright Transmitting DVB-T with a PlutoSDR
Muxwright Transmitting DVB-T with a PlutoSDR

AI Disclaimer: The project's GitHub commit history lists Claude as a co-author.

Mobile-Whip: A Compact Battery Powered Mini-Whip Style Active HF Antenna for Handhelds and SDRs

Thank you to RTL-SDR.COM reader Ernie (NH7L), who wrote in and wanted to share news about the “Mobile-Whip” antenna, an open-source active receive antenna from GitHub user skuep.

The design is based on the well-known PA0RDT Mini-Whip, but it is built for portable use. It runs from a single 18650 lithium cell with an onboard USB charger, or from 5V USB, the 4.5V bias tee on the RTL-SDR Blog V4, or a standard 12-15V Mini-Whip bias tee. It uses an ultra-low input capacitance LTC6268 op-amp instead of a JFET, draws about 20 mA, and is only 200 mm long. That makes it small enough to mount directly on a handheld like an HF-modded UV-K5, a portable receiver, or a dongle SDR. It is designed for 100 kHz to 30 MHz, but the author says it also works reasonably well on FM and 2m.

The project is a first-revision preview with some known issues. A revision B with better VHF/UHF performance is reportedly in the works. There is no reverse-TX protection yet, so pressing PTT with it attached could destroy it. The KiCad files, simulations and JLCPCB-ready assembly files are on GitHub under the CERN-OHL-P-2.0 license. Assembled boards work out to roughly €25 each.

In two YouTube videos from a Polish ham, the Mobile-Whip is compared against a 27 MHz telescopic whip on several receivers, including the Radtel RT-950 Pro, UV-K5, ATS Mini, and Malahit DSP2. The tiny PCB antenna generally comes out ahead. On the RT-950 it even receives Polish Radio on 225 kHz longwave, which the telescopic whip could not. He does note that its high gain can overload receivers with poor front-end filtering.

The "Mobile-Whip" a PA0RDT Mini-Whip inspired portable antenna for HF
The "Mobile-Whip" a PA0RDT Mini-Whip inspired portable antenna for HF

SDR++ and SDR# Plugins For: FT8 / FT4 / WSPR / FST4 / FST4W / JS8 / Q65 / CW / RTTY / JS8 / Olivia / PSK31 and PSK63

Thank you to ReLLL for writing in with an update on his decoder plugins, which we previously posted about as the “Advanced FT8/FT4 DX Decoder” just yesterday. 

Kondor Weak Signal Modes Decoder is the renamed and expanded version of the original plugin. It now decodes WSPR, FST4, FST4W, JS8, and Q65 in addition to FT8 and FT4. Its features include: A day/night DX map with SNR colors, station and country statistics, a DX activity bearing display, searchable tables, SQLite and CSV logging and optional forwarding to GridTracker.

ReLLL also added a new plugin called Maverick Text Modes Decoder (formerly CW Notebook) which decodes CW, RTTY, JS8, Olivia, PSK31 and PSK63. It provides a CW transcript with Markdown logs, simultaneous frequency tabs, spectrum discovery, pinned priority signals, and RX SNR readouts.

Both plugins now support standard SDR++ 1.2.0 and SDR++Brown 1.2.1 on Apple Silicon Macs running macOS 15 or later. There is also now a downloadable Windows preview for SDR#.

ReLLL welcomes reception reports, bug reports and UI ideas via GitHub Issues or X @FoxOnTheRunTr.

Kondor Weak Signal Modes Decoder
Kondor Weak Signal Modes Decoder

Advanced FT8/FT4 DX Decoder: A Native FT8/FT4 Decoder Plugin for SDR++Brown on macOS

Thank you to ReLLL for writing in and sharing news about the release of his "Advanced FT8/FT4 DX Decoder", a free and open-source plugin for SDR++Brown running on Apple Silicon Macs. SDR++Brown is a popular unofficial fork of SDR++ that already includes some built-in FT8 decoding capabilities. This plugin builds on that and adds a full DX monitoring workspace directly inside the SDR software, so there is no need to pipe audio out to WSJT-X just to see who you’re hearing.

The plugin decodes FT8 and FT4 and plots received stations on a DX map. It also displays tables of unique stations, all decoded messages and countries heard, along with receiver SNR and approximate distances calculated from grid locators. Other features include table filtering and sorting, persistent CSV reception logging, optional waterfall notifications, and a WSJT-X format UDP output that can feed GridTracker directly. Decoding also continues in the background even when the plugin window is closed.

We note that the latest release also adds decoding for WSPR, FST4, FST4W and Q65. Note that the plugin is not intended for use with standard SDR++, or on Windows or Linux. Installation instructions are on the GitHub page, and a user guide is also available.

Advanced FT8/FT4 DX Decoder plugin for SDR++Brown
Advanced FT8/FT4 DX Decoder plugin for SDR++Brown