Category: RTL-SDR

Tracking Tagged Orangutans in the Bornean Jungle with Drones, GNU Radio and an Airspy Mini

Due to various human activities causing the environmental destruction of it's habitat, the Orangutan is now classed as a critically endangered species. In addition to being endangered, Orangutans face another problem in that they are often captured and sold as pets due to their intelligence and cuteness.

To combat these problems, NGOs, charities and rescue centers have been using RF tags on rehabilitated Orangutans that have released back into the wild. The RF tag regularly transmits a data-less pulse at VHF frequencies which is then typically tracked using direction finding equipment such as a directional Yagi antenna. The range is only approximately 200-400m. 

In order to try and alleviate the range issue Dirk Gorissen has been working on creating a drone based system that could detect the VHF transmission and create a heatmap of Orangutan positions. The first iteration of his system uses an RTL-SDR, Odroid and lightweight loop antenna. A simple Python script then monitors the spectrum and logs the drones current location, altitude, speed and heading when a pulse is detected. Tests confirmed that the signal was able to be detected from the sky, but unfortunately the drone was eventually crashed and lost before it could be properly used.

In his second try a few years later, Dirk used a larger drone and switched SDRs to an Airspy Mini with preamp. The pulse detection code was also improved by using GNU Radio to create a DSP algorithm combining peak detection, cross correlation with a known template of the signal, and a phase locked loop. Visualization and data transfer is achieved through react.js and a Flask web server running on the drones WiFi hotspot. This time with the new drone and system Dirk was able to successfully detect and locate several Orangutan's on various flights, despite noting that some RF tags appeared to be glitchy.

Orangutan Detected with Drone, Airspy Mini and GNU Radio.
Orangutan Detected with Drone, Airspy Mini and GNU Radio.
Drone used in the experiment
Drone used in the experiment

Using an RTL-SDR to Monitor A Tire Pressure Sensor used in Home Brewing

Over on YouTube Andreas Spiess has been helping his friend create a pressure monitoring system for his home brew beer bottles. In order to do this, Andreas uses an externally mounted after market wireless tire pressure sensor whose data can be received with an RTL-SDR and the rtl_433 decoder software. Modern vehicle tires contain a TPMS (tire pressure monitoring system) sensor, which keeps track of tire pressure, temperature and acceleration. The data is wirelessly transmitted via 433 or 315 MHz to the cars dashboard and computer for safety monitoring.

In the first video Andreas discusses tire pressure monitors and how they could be used for other non-tire applications, talks a bit about the wireless protocol used, and how to reverse engineer it. He notes that the author of rtl_433 was able to implement his particular tire pressure sensor brand's protocol into the rtl_433 database, so now anyone can decode them. Finally in this video he also shows that he can easily spoof a flat tire signal using a HackRF and GNU Radio which might cause a modern high end car to refuse to move.

The second video shows how to continuously monitor that TPMS data for the home brew set up. Andreas uses an RTL-SDR and Raspberry Pi running rtl_433, which outputs it's data into Mosquitto, Node-Red, InfluxDB and the Grafana. These programs help to read, manage, log and graph the data. The rtl_433 program is also monitored by Supervisord which automatically restarts rtl_433 if the program crashes.

If you are interested, there is a related video that was uploaded in between the two shown below which shows how he created a 3D printed cap to mount the valve and tire pressure sensor on the beer bottles.

#261 Measure Pressure Remotely (including TPMS Hacking / Attack) for Beer Brewing

Safely Monitor and Alarm with Supervisord and Telegram

NOAA-APT Software Decoder: Users Guide Now Available

Back in August, 2018 we posted about NOAA-APT, which back then was a new NOAA APT image decoder program. Recently Martin, the author of NOAA-APT has written in and wanted to note that he's now created a guide and video tutorials for his software, and for NOAA APT reception in general.

NOAA weather satellites broadcast an Automatic Picture Transmission (APT) signal, which contains a live weather image of your area. With an RTL-SDR and antenna they can be received and downloaded every time one of the satellite's passes overhead which could be multiple times a day.

Our standard NOAA weather satellite tutorial makes use of SDR#, audio piping and the WXtoIMG to receive NOAA satellite images. Martin's guide and software might be slightly easier for newbies as it only involves recording an audio WAV file, then loading it up into his software. The disadvantage is that the image is not colorized, and not displayed in real time as it is in WXtoIMG.

As you may already know, the old standard software in NOAA image decoding, WXtoIMG, is now considered abandonware, and the only place to get it is from a third party mirror rehosting the now defunct WXtoIMG website. As WXtoIMG is closed source no further development can occur on it. Martin's NOAA-APT still misses a lot of the advanced features of WXtoIMG but it is fully open source and multiplatform, and so it is a very promising program.

Receiving NOAA satellite images with noaa-apt and SDR#

QIRX SDR Now Shows Received DAB Transmitters on A Map

QIRX SDR is an RTL-SDR compatible program that focuses on DAB+ decoding and listening. In a recent update programmer Clem notes that the newest feature is a map powered by OpenStreetMap that can display a the location of received DAB stations. He writes

The main new feature is the integration of Openstreetmap to display the locations of DAB transmitters (please see attached picture of a raw recording from England), together with the own position of the receiver.

In case the transmitter ident code (TII) is detected and the transmitter is contained in the database, it is displayed on the map as an icon, colored according to the TII signal strength.

The "Own Position" is indicated as a red or green dot, either (without GNSS sensor) placed by dragging the red circle with the mouse to its correct position, or by attaching a GNSS (GPS or GLONASS) sensor.

When recording raw I/Q data, the GNSS positions are written into a second file, parallel with the .raw file. On replaying, the current recorded geolocation is displayed synchronously to the recorded transmitters on the map. This might be useful in a mobile environment. The distances are displayed in the TII table.

The transmitter database comes from two sources:

  • UK: Public OFCOM database,
  • Rest of Europe: DABLIST (, as provided by the UKW/TV Arbeitskreis e.V. (

Currently, both databases are merged into a single, local Excel file, serving as the data source to the software.

QIRX SDR Screenshot with OpenStreetMap and Received DAB Transmitter Locations Showing
QIRX SDR Screenshot with OpenStreetMap and Received DAB Transmitter Locations Showing

A More In-depth Look at the Tunisian RTL-SDR Espionage Story

The Africa Report, an online newspaper specializing in African stories recently ran a story titled "A Tunisian spy story". The story discusses the circumstances behind the mysterious arrest of a UN expert in Tunisian, supposedly for having used an RTL-SDR dongle as part of his research into violations of the UN arms embargo on Libya. See our previous post for the original details.

The Africa Report story gives a more in depth look at what happened during his arrest and what is happening in Tunisia. If you're interested in following this story, this is a good read.

An RTL-SDR aircraft tracker, which can be purchased legally on the internet, is composed of an antenna and a USB key. There are smartphone apps that have similar functionalities that allow you to track commercial flight routes. Can it be that this object, found in his home, is the sole piece of evidence used by the Tunisian courts to justify the detention of United Nations (UN) expert Moncef Kartas for espionage, as his defence claims?

Kartas, who is German-Tunisian, was officially mandated in 2016 by the UN to lead an investigation into violations of the arms embargo on Libya. His carefully selected team was appointed by the UN secretary general and were due to draft a report in June. Kartas’s arrest disrupted those plans.

Kartas was arrested as he walked off a plane on 11 April in a theatrical scene at Tunis airport involving around 10 security agents. He is now awaiting trial in his cell in Mornaguia prison. Accused of “treason” and “spying for a foreign power”, he faces the death penalty. Fortunately for him, Tunisia has banned that punishment.

Rumours are running high around the activities of a security company he co-founded and the role of a second man who was also arrested. But several pieces are missing from the puzzle. The versions of the Tunisian authorities and the UN are completely different, as is the information supplied by the defence and that supplied by the prosecution. Saying it is “very concerned”, the UN is calling for the researcher’s release, pointing out that the lifting of his immunity is illegal.

[Read More]

UPDATE: Kartas was recently freed on bail.

SignalsEverywhere: P25 Trunking with Just One RTL-SDR and DSDPlus Fastlane

Over on YouTube Corrosive from the SignalsEverywhere channel has uploaded a new video showing us how to set up P25 trunking and decoding with DSDPlus Fastlane and only a single RTL-SDR.

Normally two dongles are required to follow a P25 trunking system. One dongle continuously receives the trunking channel, and a second tunes to the voice channel chosen by the trunking channel. However, the latest DSDPlus Fastlane has a feature that allows one only dongle to be used. It works by tuning back and forth between the control and voice channel. The disadvantage is that trunking information could be missed while tuned to a voice channel, so some calls could be missed.

RTL SDR Setup P25 Trunking With 1 SDR and DSDPlus FastLane

Osmocom Now Releasing Weekly Windows Binaries for RTL-SDR and Osmo-FL2K

Osmocom is the open source team behind the RTL-SDR driver project and the Osmo-FL2K discovery. In a recent announcement they have noted that they are now publishing weekly binary builds for the RTL-SDR and Osmo-FL2K projects. This means that Windows users are now able to test the latest driver updates without having to compile them manually. Laforge writes:

While Osmocom in general is a very much Linux-centric development community, we are now finally publishing automatic weekly Windows binary builds for the most widely used Osmocom SDR related projects: rtl-sdr and osmo-fl2k.

You can find the binaries at The actual builds are done by roox who is building them using MinGW on OBS, see

The status of the osmocom binary publish job, executed once per week from now on, can be found at

As a reminder, if you've ever enjoyed the RTL-SDR or Osmo-FL2k projects, you can thank Osmocom for bringing them to us for free by donating to them at Open Collective. The drivers are the root of all that we can do with RTL-SDR and FL2K, so it is only fair to thank them.

Stratux 1090 MHz + 978 MHz Diplexer Now Available

Recently the company Stratux released a new ADS-B/UAT diplexer PCB. This is useful if you have a single antenna and want to feed two RTL-SDR dongles, with one receiving 1090 MHZ ADS-B and the second receiving 978 MHz UAT. The filter consists of a splitter and two SAW filters.

ADS-B is short for Automatic Dependant Surveillance Broadcast and is used to help track aircraft in the sky. It is transmit at 1090 MHz and the signal contains aircraft data such as the location, speed, altitude and aircraft call sign. ADS-B is utilized worldwide.

UAT is short for Universal Access Tranceiver and is transmit at 978 MHz. Like ADS-B it is used to keep track of aircraft, however UAT is only available in the USA and only for aircraft that fly below 18,000ft. It is a little cheaper and unlike ADS-B, UAT transmissions can also contain weather and traffic data.

US aircraft owners/operators that fly below 18,000ft can choose to install either UAT or ADS-B transmitters in their aircraft, so in the US a complete monitoring solution needs to monitor both 1090 MHz and 978 MHz.

The Stratux Diplexer board is currently available on Amazon for $24.99.

Stratux Diplexer for 1090 MHz ADS-B and 978 MHz UAT.
Stratux Diplexer for 1090 MHz ADS-B and 978 MHz UAT.