Category: Digital Signals

Help Support RadioCapture – A Project that Records Entire Trunked Radio Systems and Provides Online Access to Audio is a website run by Matt Mills that is capable of automatically capturing trunked radio communications from various agencies such as the emergency services and creating publicly accessible historical and live logs of the audio. This is a concept different to radio scanner streams, as all audio is logged and historical audio can be accessed easily at any time.

The system is based on SDR hardware such as the RTL-SDR. Currently Matt runs a receiver in Denver and captures Denver PD which can be listened to on the site without needing to log in. Once logged in (registration is free), other talkgroups available include various agencies in Colorado, New Jersey and Pennsylvania. currently available Talkgroups being logged Currently available talkgroups being logged

Recently Matt has put a call out for people to help support the site via Patreon. He notes that RadioCapture is currently run as a hobby, but with monetary support he hopes to be able to expand the site into a business and have receivers listening and uploading worldwide. He writes:

Hey! Thanks for supporting the continued operation and development of This is a hobby project I've been working on this since late 2011. I'd like to turn it into a real business with your help. is a software defined radio system I built that captures entire trunked radio systems. It demodulates and captures every call on every channel of one, or many systems.

A single RadioCapture server can capture hundreds of simultaneous voice transmissions and a bunch of sites, additionally it's designed in such a way that it can run across multiple computers. My biggest RF site uses 3 machines to capture 19 P25 systems, and easily hits more than 100 active voice channels recordings simultaneously every day.

Matt has also noted that if the site is able to become self-sustaining via Patreon, he hopes to also be able to bring out a RadioCapture kit consisting of 10-16 RTL-SDR dongles, hubs and cables which would allow anyone to easily capture and upload almost all trunked communications from their area. He also notes that at the time of writing:

RadioCapture has 701790271 unique recordings of 503779875 unique transmissions (some calls get captured on multiple transmitters) from the 21 systems that have been captured

If you're interested in talking to Matt about the site, you can also join his Rocket.Chat room at

RadioCapture logged audio
RadioCapture playing logged audio

SignalsEverywhere: Setting Up Priority and Groups in DSDPlus Fastlane

In his last video, Corrosive from the SignalsEverywhere YouTube channel showed us a quick guide on setting up a Phase 1 P25 digital voice decoder with two RTL-SDR dongles and the DSDPlus Fastlane decoder.

Now in his latest video Corrosive continues with the DSDPlus tutorial and this time explains how to set up priority and groups. On a trunked radio system there may be many different agencies using the same system simultaneously. Without priorities and groups, you would be listening to all communications in the system, and following a conversation within a particular agency would be difficult. Setting up priorities and groups allows you to filter out the conversations that you are not interested in, allowing you to focus on listening in to a particular agency only.

RTL SDR Digital Radio Scanning Priority and Groups With DSDPlus Fastlane Setup Tutorial

SignalsEverywhere: Using DSDPlus Fastlane for Listening to Phase 1 P25 Trunking

DSDPlus is a popular piece of software often used with RTL-SDR dongles to listen to unencrypted digital voice signals such as P25 and DMR. Digital voice is now commonly used by many Police and emergency services as well as business radio. DSDPlus fastlane is DSD's paid upgrade which allows subscribers to access to the latest releases of DSDPlus early.

Over on the SignalsEverywhere YouTube channel, Corrosive has uploaded a quick video guide that shows how to use DSDPlus Fastlane and two RTL-SDR dongles to set up a Phase 1 P25 voice decoder that automatically follows a P25 trunking channel. The basic process involves running two FMP instances which is a program in the DSDPlus suite that connects to the RTL-SDR's and receives the signal. One DSDPlus instance monitors the trunking channel, and this tunes the second FMP+DSD instance to the frequency currently active in the trunking system.

Corrosive also explains how people who are subscribed to RadioReference can download pre-populated data files that will allow the DSDPlus event log to display talkgroup information so that you can see who is talking to who.

Digital Radio Scanning With DSDPlus Setup Fastlane | Tracking Phase 1 P25 Trunking System Tutorial

A Worldwide Map for HRPT Weather Satellite Receive Stations

Recently Manuel (DO5TY aka Tysonpower from YouTube) wrote in and wanted to share his website that shows HRPT weather satellite receive stations from around the world on a map, and links to their Twitter pages where you can see the latest images that have been uploaded. The database also describes the SDR and antenna equipment used by each station. Currently there are 10 stations on the map, and Manuel encourages other people to submit their stations to the map database too. If you are interested in contributing your station to the map, please see Manuel's blog post for more information.

Since the satellite broadcasts a live image of what is currently being seen by the weather camera, each receiver location receives a live view of their part of the earth only. The end goal of Manuel's HRPT station map is to crowd source and collect multiple images of different parts of the earth to create a large HRPT composite image. In a previous post, Manuel who is based in Germany was able to create a beautiful composite image covering Germany, the Atlantic Ocean and Canada with the help of a station in Canada. With more contributors larger and more complete composite images of the Earth could be created.

HRPT is a high resolution weather satellite image signal that is broadcast from the same NOAA satellites that provide the more commonly received low resolution APT images at 137 MHz. HRPT is also broadcast from the Feng Yun and Metop-A satellites. However, HRPT transmits at 1.7 GHz, so a high gain dish antenna with motorized tracking mount, LNA and high bandwidth SDR like an Airspy is required to receive it.

HRPT Station Map
HRPT Station Map

YouTube Tutorial: Decoding POCSAG and FLEX Pager Messages on Windows with PDW

Pager systems are famously known to be insecure, and due to the lack of encryption and high transmit power anyone with an RTL-SDR or other SDR can receive and decode pager messages. The users of pagers are mostly hospitals and doctors, and IT infrastructure professionals who need to be notified of server warnings and errors quickly. We have a text tutorial on decoding these messages with an RTL-SDR available here, and there are several previous posts discussing how insecure they are. 

If you prefer a video tutorial, M6LME on YouTube has recently uploaded one where he explains the PDW pager decoding software, the VB-Audio 'banana' audio mixing software, and how to use SDR-Console with an RTL-SDR and the aforementioned software to receive and decode the signal.

How to Decode POCSAG & FLEX using an RTL-SDR Dongle

YouTube Tutorial: Eavesdropping on DECT6.0 Cordless Phones with a HackRF and GR-DECT2

Back in December of last year Corrosive from his YouTube channel SignalsEverywhere showed us a demo video of him receiving unecrypted DECT digital cordless phones with his HackRF.

DECT is an acronym for 'Digital Enhanced Cordless Telecommunications', and is the wireless standard used by modern digital cordless phones as well as some digital baby monitors. In most countries DECT communications take place at 1880 - 1900 MHz, and in the USA at 1920 - 1930 MHz. Some modern cordless phones now use encryption on their DECT signal, but many older models do not, and most baby monitors do not either. However, DECT encryption is known to be weak, and can be broken with some effort.

In his latest video Corrosive shows us how to install GR-DECT2 on Linux, which is the GNU Radio based decoding software required to decode the DECT signal. He then goes on to show how the software can be used and finally provides some optimizations tips.

DECT 6.0 Cordless Phone Eavesdropping {Install GR-DECT2 and Decode with HackRF SDR}

Tracking Radiosondes with an RTL-SDR and Radiosonde_Auto_RX

A radiosonde is a small sensor and radio package normally attached to a weather balloon. Meteorological agencies around the world typically launch two balloons a day from several locations to gather data for weather prediction. With an RTL-SDR, appropriate antenna and decoding software it is possible to decode the telemetry signal and gather the weather data yourself. You can also use the GPS data to chase and collect the fallen radiosonde package. We have a tutorial on setting up a basic radiosonde decoder in Windows here.

However, if you want to set up a permanent radiosonde receive station it's possible to create an automatic system with a program called radiosonde_auto_rx. It works by performing an rtl_power scan over the radiosonde frequency range and looking for peaks that might indicate that a radiosonde is currently transmitting. If a peak is found it tries to decode it as a radiosonde, and if successful will begin uploading the weather data to an online aggregation site called With this sort of system there is no need to know in advance the launch times and exact frequencies that your local meteorological agency uses, as often this information is not public.

Recently Mark Jessop and Michael Wheeler, the team behind radiosonde_auto_rx, also did a talk at the conference. The talk explains radiosondes and demonstrates their software in action. They then go on to talk about chasing radiosondes, and re-purposing collected sondes.

[Also seen on Hackaday]

STM32 Development Boards (literally) Falling From The Sky

SDR# TETRA Plugin Now Available At RTL-SDR.RU

Vasilli has recently released the SDR# TETRA plugin on his website RTL-SDR.RU (note that the site is in Russian, but can be translated with the Google Translate option in the top right of the page). Previously it was only available via ever changing forum links, so it's good to see that it has a permanent home now for the latest version. This plugin allows you to listen to TETRA digital voice via SDR#, without needing to set up any complicated GNU Radio based receivers which were necessary in the past.

The features include (note Translated from Russian):

  • Receiving a signal from the BS band 25kHz and modulation Pi / 4-DQPSK;
  • Automatic adjustment of the reception frequency;
  • Displays information about the BS;
  • Displays ISSI, GSSI subscribers in the channels (for open channels only);
  • Displays a service exchange network (for open channels only);
  • It allows you to listen to the channels in manual or automatic mode selection (only open channels);
  • It allows to filter and distribute the listening priority specified for groups (GSSI);
  • It displays a message with the location (just a short message format)

The current features not yet implemented are:

  • And listen to correctly display any encoded information in a network;
  • Display SDS type 4 (short messages);
  • Record audio from the channels (menu added, but does not work);

We also note that as discussed in a previous post there is a companion program for this plugin called TETRA Trunk Tracker.

SDR# TETRA Decoder Plugin
SDR# TETRA Decoder Plugin