Category: Applications

Creating an Open Source DMR Transceiver with a LimeSDR Mini

Thank you to Adrian Musceac for writing and sharing his article detailing how he implemented an open-source DMR (Digital Mobile Radio) transceiver modem with his LimeSDR Mini and GNU Radio.

DMR is a digital voice communications protocol often used by commercial business band radios, as well as by amateur radio hobbyists.

Adrian explains:

I wrote an article about the implementation of an open-source DMR transceiver using the LimeSDR-mini, GNU Radio and Codec2, which could be used for SDR experiments.

The DMR modem was designed to work both in repeater and direct (DMO) mode, and supports voice and other basic features of the ETSI TS 102 361-1 standard.

In the article there is discussion about aspects of the TDMA transmission, time synchronization, as well as how David Rowe's Codec2 can be used to replace the default vocoder.

The work builds upon Jonathan Naylor's extensive DMR implementation which a large number of amateur radio operators are using as part of MMDVM.

DMR TX Flowgraph
DMR TX Flowgraph
Transmitting DMR with the LimeSDR-mini

DragonOS: LTE IMSI Sniffing using the LTE Sniffer Tool and an Ettus X310 SDR

DragonOS creator Aaron recently uploaded a video on YouTube showing how to capture IMSI data from an LTE-enabled phone by using the open-source LTE sniffer tool and Ettus X310 software-defined radio.

In the video, Aaron uses a simulated environment involving a Signal SDR Pro to simulate the LTE cell phone, a B205 Mini operating as the eNodeB (base station), and an Ettus X310 SDR for the actual LTE sniffing. The SRSRAN software running on DragonOS is used to simulate the LTE network environment.

Aaron goes on to show how the LTE sniffer software passively decodes the physical downlink control channels and captures IMSI numbers from user cell phones.

An IMSI is a unique identifier associated with a cell phone user's SIM card. IMSI sniffing cannot be used to listen to or decode voice, text, or data as they are all encrypted. However, bad actors can use IMSI sniffing to track the movement of devices/people.

DragonOS Noble Sniff + Passively Capture LTE IMSI (x310, b205mini, SignalSDR Pro)

New Khanfar Software: Spot Scanner, Phased Based DF, IQ Playback

Recently, software developer M. Khanfar has been releasing a lot of new SDR and RTL-SDR compatible software including a Spectrum Analyzer and FM demodulator, directional antenna based radio direction finder, and a gr-phosphor based spectrum visualizer.

His pace of development continues, and recently he's developed three new programs.

The first is Khanfar Spot Scanner, a tool for detecting active signals. 

Khanfar Spot Scanner is a powerful and feature-rich spectrum analyzer designed for radio frequency enthusiasts, wireless security researchers, and professional RF engineers. Supporting multiple SDR hardware devices including RTL-SDR, Airspy, and HackRF, this software provides comprehensive spectrum visualization, automated signal detection, and in-depth analysis reporting.

Khanfar Spot Scanner

The second software is called "Khanfar Phase-Based Direction Finding" a tool for phase based radio direction finding.

Khanfar Phase-Based DF is advanced direction finding software that uses phase difference analysis to determine the bearing of radio signal sources. Unlike traditional direction finding systems that rely on directional antennas and signal strength comparison, this software utilizes an array of omnidirectional antennas and sophisticated signal processing algorithms to analyze the phase relationships between received signals.

We want to add to this a note that we're not entirely sure how this software can possibly work as phase based direction finding with RTL-SDRs requires synchronized clocks, and sample and phase alignment to be performed via a correlation with a noise source first which this software does not enable. Without those steps taken results will be totally random. We gave this software a brief test with a KrakenSDR, but as expected, did not see the results we expected. We're keen to hear feedback from other users.

Khanfar Phase-Based Direction Finding Software

The third program is called "Khanfar IQ Live-Rec-Playback" a tool for recording and playing back IQ files, with IQEngine integration.

Khanfar RTL-SDR IQ Live+Rec+Playback is a powerful, feature-rich spectrum analyzer application designed for RTL-SDR devices. This professional-grade software provides real-time RF spectrum visualization with GPU-accelerated rendering, comprehensive IQ data recording capabilities in multiple industry-standard formats, and advanced playback features for signal analysis. With IQEngine and IQ Analyzer integration, you can seamlessly export your recorded signals for comprehensive online analysis, visualization, and collaboration.

Khanfar IQ Live-Rec-Playback

GOES-19 Completes Transition to GOES-EAST Replacing GOES-16

NOAA GOES satellites are a popular way to receive beautiful full-disk weather images of the Earth using an RTL-SDR, antenna hardware such as the Discovery Dish, and software such as SatDump. The GOES-EAST satellite covers North and South America and was provided by GOES-16 until April 7th.

Over the past few months, NOAA has been moving the GOES-16 satellite into a storage orbit and the newer GOES-19 satellite, which was launched in June 2024, into the GOES-EAST position. Recently, on 7 April 2025, this transition was completed, and the GOES-16 was turned off, and the GOES-19 signal was activated.

For SatDump users, no configuration changes should be necessary to receive signals from GOES-19. However, Sanchez users will need to update their configuration file.

If you're interested, Carl Reinmann, owner of the usradioguy.com website, provides more detailed information about the transition and activation of GOES-19.

GOES-19 Received by Carl Reinmann
GOES-19 Received by Carl Reinmann

Proposing a Software Defined Radio based “AI Battle Buddy”

Over on YouTube, Isaac Botkin of TREX LABS has uploaded a video discussing how he proposes to build an "AI Battle Buddy" with a built-in software-defined radio. The idea is to combine a wide frequency range software-defined radio with AI tools that automatically determine and alert the device owner when something interesting occurs in the radio spectrum.

Isaac gives example use cases for the device, such as alerts when jamming is detected, drone detection alerts, alerts when there is suddenly increased public safety radio traffic or if there are nearby public safety radio transmissions, and information about nearby aircraft and NOAA weather alerts.

The device is proposed to have no screen, but would simply give audio alerts via Bluetooth earpiece, or text alerts via smartphone or smart watch. 

Ultimately, such a device has yet to be built for the general consumer market, but Isaac notes that AI-SDR devices like the Anduril Pulsar already exist for the military consumer.

How to Make an AI Battle Buddy for Electronic Warfare

IEEE Spectrum Article on Discovery Dish

Electrical engineering magazine IEEE Spectrum has recently posted an article about our Discovery Dish product, which was successfully crowd-funded on CrowdSupply and delivered to initial backers early this year. Discovery Dish is a 70-cm aluminum satellite dish with an active filtered feed. It is designed for receiving real-time weather data from GOES HRIT, GK-2A LRIT, FengYun LRIT, NOAA HRPT, Metop HRPT, Meteor M2 HRPT, and other weather satellites that operate around 1.69 GHz. There are also feeds for Inmarsat satellites, Hydroden Line observation, and S-band satellites.

In the article, Stephen Cass introduces the Discovery Dish, highlighting its practical uses and the convenience of disassembling it for easy packing in a suitcase during travel. He also shares his experience using the Discovery Dish to successfully receive images from the GOES-East satellite from the rooftop of his New York City apartment.

Finally, he mentions how he tested the hydrogen line feed as well, successfully seeing a hydrogen line peak when pointing at the galaxy.

Image from the IEEE Spectrum Article on Discovery Dish
Image from the IEEE Spectrum Article on Discovery Dish

ADALM PlutoSDR Spectrum Analyzer: Sweep from 100 MHz to 6 GHz

Thank you to RTL-SDR.COM reader Maka for sharing his latest software for the ADALM PlutoSDR, "ADALM PlutoSDR Spectrum Analyzer." The software is a sweeping spectrum analyzer that uses the 'lock-in amplifier techniques' and it allows you to view the entire 100 MHz to 6 GHz tuning range of the PlutoSDR.

The program is an open-source MIT-licensed Python script that can be run on Linux systems. Instructions to install and connect to the PlutoSDR are available on the program's GitHub page. Maka has also provided a YouTube video (embedded below) demonstrating the software and explaining the lock-in amplifier technique used in his software, as well as two other videos, one explaining the code, and another showing how to measure a filter with it.

Maka writes:

I built an open-source real-time spectrum analyzer using the ADALM Pluto SDR and Python. It allows you to sweep across wide frequency ranges (100 MHz to 6 GHz) and visualize RF signals like Wi-Fi, LTE, GSM, and Bluetooth in real-time.

It includes a custom PyQt GUI with:

  • Adjustable sweep parameters
  • Peak hold
  • Threshold alerts
  • Draggable markers
  • Highlighted known bands
  • Data export to CSV
See Invisible Electromagnetic Waves Around You with ADALM Pluto SDR Spectrum Analyzer + Code

Spectrum SDR: New Android App for RTL-SDR FM/AM Decoding and Spectrum Viewing

Thank you to James Mainwaring of Knowle Consultants for submitting news of the release of his latest Android app called "Spectrum SDR" for RTL-SDR. Knowle Consultants have previously released a range of RTL-SDR Android apps for FM, Airband, Ham FM and ADS-B reception. The new Spectrum SDR app has a spectrum viewer, as well as the ability to demodulate AM and FM signals.

James writes the following about Spectrum SDR:

This application is about having a bit of fun with those amazing little RTL-SDR dongles, whilst listening to AM/FM radio signals. It's nice and easy to use so why not give it a try?

- Covers the full frequency range of your RTL-SDR dongle
- AM and FM, wide and narrow
- FFT display
- Sample rates 240000 Hz to 2160000 Hz
- Bias tee control
- 75 presets over 5 pages
- Gain controls
- Squelch
- Built-in help

Spectrum SDR Android App Screenshot
Spectrum SDR Android App Screenshot