Over on her YouTube channel SignalsEverywhere, Sarah has uploaded her latest video showing how it is possible to monitor Itron ERT smart meters on an Android device. Smart meters are used to wirelessly monitor the usage of residential utilities such as water, gas, and electricity. With an RTL-SDR and some decoding software, it is possible to monitor the data coming from your own and your neighbours meters (at least for certain brands of meter).
In her video, Sarah shows how she compiled the rtl_amr decoder software for Android, and created her own Android app called "AndAMR" for displaying the data decoded by rtl_amr. The rest of the video shows how to set up and use the app.
Over on his YouTube channel, Aaron, creator of DragonOS and WarDragon has uploaded a video showing how it is possible to decode Meshtastic with an RTL-SDR and GNU Radio project called Meshtastic_SDR.
If you weren't aware of it, Meshtastic is software that enables off-grid mesh network based communications and can run on cheap LoRa hardware. The mesh based nature of the system means that communications can be received over long distances, without any infrastructure, as long as there are sufficient Meshtastic nodes in an area that are able to route the message to the destination node. One example application of Meshtastic is to use it as a mesh-based text messaging system. This might be useful for teams of hikers, pilots, or skiiers who operate in remote areas without cell phone coverage.
In the video, Aaron shows how to install the Meshtastic GNU Radio software on DragonOS (Linux), and how to run the GNU Radio flowgraph and Python decoder script. Later in the video Aaron shows some test text messages being received by the software.
The Meshtastic_SDR project can also be used to transmit Meshtastic messages with an appropriate TX-capable SDR.
WarDragon Real-Time Decoding Meshtastic w/ GNU Radio & SDR (RTLSDR v3)
Welcome back to Sarah from the SignalsEverywhere YouTube channel who has recently returned to producing videos from a hiatus. In her latest video, Sarah shows off her new OP25 Mobile Control Head Android App which allows you to implement a full P25 digital radio scanner at a fraction of the cost of a commercial digital scanner. In the past, Sarah had released a similar application written for the Raspberry Pi but has decided to shift her focus to writing an equivalent Android app that is less clunky and can be deployed for a lower cost.
The app controls and displays information from the OP25 software that runs on a Raspberry Pi with RTL-SDR connected. It works by using a server application on the Raspberry Pi that manipulates the OP25 instance and its configuration files.
Sarah writes:
The application is a wrapper for OP25 that uses a raspberry pi and an android device to provide users with a mobile control head for their OP25 P25 scanner setup. Currently it's just a basic application but I'll be adding features like automatic site switching, etc.
Thank you to RTL-SDR.COM reader Lee. who found a recently released program called "gypsum" which enables an RTL-SDR or HackRF to be used as a GPS Receiver when combined with a GPS antenna. Phillip Tennen, the author of Gypsum notes that Gypsum can obtain a fix within 60 seconds from a cold start and that it has no dependencies apart from numpy. We want to note that it appears that Gpysum has no live decoding ability yet, as it works from pre-recorded GNU Radio IQ files.
In the past, we've shown in a tutorial how GPS can be received and decoded with GNSS-SDRLIB and RTKLIB on Windows. The new Gypsum software should work on Linux and MacOS too.
What's more, Phillip has written an incredible 4-part writeup on how Gypsum was implemented from scratch. In the write-up, Phillip introduces GPS and explains how it can even work with such weak signals that appear below the thermal noise floor. He then goes on to explain how the detected signal is decoded and turned into positional information, and how challenging it was to propagate the accurate timing information that calculating a solution requires. The write-up is presented with clear visualizations to help readers intuitively gain an understanding of the advanced concepts involved.
Thank you to Adrian Musceac (author of QRadioLink) for submitting his article about how he implemented an amateur radio DMR Tier III Trunked Radio Base Station with a LimeNet-Micro software-defined radio. DMR Tier III is a digital voice trunked radio system that employs Time Division Multiple Access (TDMA) technology. Tier III is largely based on Tier II, but adds trunking abilities which enable efficient channel access and resource allocation.
The LimeNET Micro is a software defined radio based on the LimeSDR, but it has some upgraded specifications such as an embedded Raspberry Pi Compute Module 3+ that make it easier to deploy as a base station.
Adrian writes:
The Tier III extension (trunked radio) to the DMR standard is defined and specified by the European Telecommunications Standards Insititute (ETSI) in the TS 102 361-4 document.
The project uses LimeNet-Micro, LimeSDR-mini or Ettus USRP hardware to set up such a base station for experimental and amateur radio digital voice communications purposes. The core components of this project are MMDVM, MMDVMHost (both under the form of forks supporting communication via ZeroMQ and pseudo-TTY), GNU Radio, DMRGateway, QRadioLink and the DMR trunked radio controller GUI.
Since DMR trunked radio is not very well known and used in the amateur radio world, I hope this will bring some new information to amateurs interested in these digital voice communication technologies. All code used is available as free and open source software (FOSS). A demo of the project used with real world amateur radio communications can be found on the page.
Back in 2021 we posted about a SDR# plugin that allowed you to interface with rtl_433 from within SDR#. RTL433 (rtl_433) is a commonly used RTL-SDR command line program that provides decoders for a wide range of 433.92 MHz, 868 MHz, 315 MHz, 345 MHz, and 915 MHz ISM band devices. Examples of such devices include weather stations, alarm sensors, utility monitors, tire pressure monitors and more.
Recently there have been a few updates to the plugin after a years hiatus which probably meant that the older version was not compatible with newer versions of SDR#. But there are also several bugfixes and minor changes made to the plugin too which can be read about on the GitHub Readme.
To download the plugin we recommend clicking on the green <>Code button on the GitHub page and choosing Download Zip. You can then browse to the install/1.5.6.2 folder. Copy the three .dll files into the Plugins folder in your SDR# directory. Then open SDR#, go to the main hamburger menu -> plugins -> RTL_433.
Thank you to Mike for writing in and sharing with us his video detailing how he makes use of a Raspberry Pi 5, touch LCD Screen and RTL-SDR to create a portable and low cost P25 police scanner. Mike notes that the cost of his system is $250, which is a lot cheaper than a comparable $600 P25 scanner.
Here is my latest weekend project; a Raspberry Pi 5 with an RTL-SDR dongle running SDRTrunk software. It is configured to listen to the local LAPD channels and runs great! The chip gets a bit hot so I think I need to add a fan.
Building a $600 P25 Police Scanner for $250!!! (SDR-Pi)
A MMDVM is usually a computing device running multiple radios, each of which is used for a separate channel with it's own filters and power amplifier hardware. Each channel can run a separate protocol if desired.
However in order to save on radio hardware, Adrian wanted to use his LimeSDR as the radio hardware in his MMDVM system. The LimeSDR is a transceiver which has enough bandwidth to implement several channels just by itself. To do this Adrian uses his MMDVM-SDR software.
His implementation runs multiple instances of MMDVM-SDR, one instance for each channel. Then a GNU Radio flowgraph with LimeSDR block connects to each of these instances, transferring data between GNU Radio and MMDVM-SDR via ZeroMQ or TCP sockets. The bulk of Adrian's post explains the architecture in detail. Adrian writes:
The setup can transmit 7 digital carriers in 200 kHz occupied spectrum, and each radio channel can be assigned to a different mode or digital voice network as configured in MMDVMHost.
This is based on the work of Jonathan Naylor G4KLX and Rakesh Peter (r4d10n).
Adrian also notes that this is still a work in progress and there are still several limitations including high latency and issues with filtering, overload and poor channel rejection.
