Category: Applications

SignalsEverywhere: A Front End GUI Control Head for OP25

Sarah from the SignalsEverywhere YouTube channel is back and this time showing off a new program she has created called "Pi25" or "OP25 Mobile Control Head". The program is a Python GUI for OP25 which runs on almost any platform including Android and Windows. OP25 is an advanced open source digital voice P25 Phase 2 capable decoder which can be used with an RTL-SDR and run on a Raspberry Pi.

Sarah's GUI software allows information from the OP25 software to be displayed on a nice large Android tablet screen, as well as having scanner forward/back buttons, and talkgroup skip and hold controls. This is very useful for in-car control on a mobile setup.

Sarah notes that she is also considering running a Kickstarter for a physical hardware OP25 head unit controller so please let her know in the YouTube video comments if you are interested.

P25 Police Scanner Control Head OP25 SDR Raspberry Pi or Android GUI Front-End

Frugal Radio: SDR Guide Ep 9 – P25 LSM Trunking with one RTL-SDR V3 and DSDPlus

In his latest episode of his SDR Guide series Rob from Frugal Radio provides a walkthrough on using DSDPlus Fastlane to decode trunked P25 with just one RTL-SDR V3 dongle. In the video he explains each of the various DSDPlus windows, and demonstrates decoding of a Simulcast system in his area.

DSDPlus is a program capable of decoding various digital audio protocols such as DMR and P25. The "Fastlane" version is a $25 paid upgrade which allows you to download the latest version that contains more features.

2021 SDR Guide Episode 9 : $25 DSDPlus P25 LSM trunking walkthrough using 1 x $25 RTL-SDRv3

Tech Minds: Decoding Orbcomm Satellites with a Software Defined Radio

Over on his YouTube channel TechMinds has uploaded a new video showing how to decode signals from Orbcomm satellites. Orbcomm run a global network of low earth orbit satellites that perform services such as Internet of Things (IoT), Machine 2 Machine (M2M) communications, asset tracking, utilities telemetry, government communications and much more. The signals can be received at around 137 MHz.

In the video he explains how the private client data is encrypted, however it is possible to at least see the encrypted data coming down, and decode some of the data management information such as the transmitted uplink frequencies using a program called Orbcomm Plotter. Ultimately, the data available is quite boring to monitor, however decoding these satellites is still an interesting exercise.

Decoding Orbcomm Satellite Transmissions Using Software Defined Radio

New SDR# User Guide Available

Paolo Romani IZ1MLL has recently created a SDR# users guide document which comprehensively explains all the features and settings available in the program. SDR# (aka SDRSharp) from is designed for Airspy SDRs, however it is one of the most popular SDR receiver programs used with RTL-SDRs as well.

Paolo's guide appears to build on our own guide at, providing new information and updates since many changes and new features have been released in SDR# since we wrote that guide a few years ago.

The guide can be found on the page and is available in English, Italian and Spanish.

SDRSharp Guide

CalibrateSDR: Calibrating your SDR Frequency Offset with DAB+

Thanks to Andreas Hornig who has recently released a new program called "CalibrateSDR" (GitHub code) which is designed to accurately determine the frequency offset of an SDR via an IQ recording of a DAB+ station.

Cheaper RTL-SDR and SDRs use a low quality crystal oscillator which usually has a large offset from the ideal frequency. Furthermore, that frequency offset will change as the dongle warms up or as the ambient temperature changes. The end result is that any signals received will not be at the correct frequency, and they will drift as the temperature changes. Higher end SDRs and improved RTL-SDRs like our RTL-SDR Blog V3 use a temperature compensated oscillator (TCXO) which has a very small frequency offset and very little temperature drift.

CalibrateSDR can be used with almost any SDR to determine the frequency offset. Andreas notes that CalibrateSDR uses the synchronization channel symbols from DAB+ digital audio stations to determine the offset. His post contains a great explanation of how this works. If you don't have DAB+ in your area, an alternative is Kalibrate-RTL which uses GSM cellphone signals to calibrate.

His results were as expected, showing that the generic RTL-SDRs have large frequency offsets, and his RTL-SDR Blog V3 and LimeSDR have much better precision.

The null symbol (lower amplitude portion) and phase reference (Orange) in a DAB+ signal

Talks and Tutorials from GNU Radio Days 2019 Now on YouTube

GNU Radio Days is a yearly European conference all about GNU Radio and its applications with software defined radios. GNU Radio is an open source digital signal processing (DSP) toolkit which is often used in cutting edge radio applications and research to implement decoders, demodulators and various SDR algorithms.

Over on YouTube talks and tutorials from the 2019 GNU Radio Days event have recently been uploaded. There are some interesting talks available including talks about SatNOGS, KiwiSDR, very long baseline interferometry radio astronomy, phase noise & digital noise explanations, as well as several tutorials with topics such as how to write a GNU Radio block and how to hack a proprietary protocol.

GNU Radio Days 2019 Talks

DragonOS: OP25 “Boatbod” P25 Phase 1 Running on GNU Radio 3.8 with RTL-SDR

DragonOS is a ready to use Ubuntu Linux image that comes preinstalled with multiple SDR program. The creator of DragonOS, Aaron, uploads various YouTube tutorials. In his latest tutorial he shows how to install the latest version of the "Boatbod" OP25 development code for receiving P25 Phase 1 on Linux with the latest GNU Radio 3.8. In the video Aaron uses an RTL-SDR, but notes it could also work with other SDRs like the HackRF.

DragonOS Focal OP25 "Boatbod" P25 Phase 1 w/ RTLSDR (GNU Radio 3.8, Python3, R9+)

SSTV from the International Space Station Scheduled for Dec 24 – Dec 31

Thank you to Maksim for submitting news that the International Space Station (ISS) will be transmitting Slow Scan TV (SSTV) in late December to celebrate 20 years of amateur radio operations onboard the space station. The ISS periodically transmits SSTV images during special events throughout the year. You can keep up to date on the ISS SSTV schedule on the ARISS-SSTV site.

An ARISS Slow Scan TV (SSTV) event is scheduled from the International Space Station (ISS) for late December. This will be a special SSTV event to celebrate the 20th anniversary of ARISS operations on the ISS. The event is scheduled to begin on December 24 and continue through December 31. Details to follow later. Dates are subject to change due to ISS operational adjustments.

With an RTL-SDR and a simple V-Dipole from our RTL-SDR Blog V3 antenna kit it is possible to receive these images when the ISS passes over. ISS passes for your city can be determined online, and the SSTV images can be decoded with a program like MMSSTV.

An example SSTV image from the last ISS SSTV event
An example SSTV image from an SSTV event held in previous years.