Category: Applications

GNU Radio Amateur Radio Meeting: A Look at Project 25 (P25) Digital Radio

Over on their YouTube channel GNU Radio have uploaded a recent talk by Aaron Rossetto titled "A Look at Project 25 (P25) Digital Radio". The talk explains the North American public safety P25 system in great depth, and is a good watch for anyone looking into details on how the system works in a deeply technical way. He later shows some examples of his P25 decoding and recording setup. Slides can be found here, and the video is posted below.

Agenda: In this presentation, I will introduce Project 25 digital radio, with a strong emphasis on its use in North American public safety trunked radio systems, and to describe experiments monitoring and decoding P25 traffic using GNU Radio code.

  • What is Project 25?
  • A brief introduction to trunked radio
  • Diving into the P25 protocol
    • Modulation
    • Packet framing and encapsulation
    • Packet types
  • GNU Radio and P25 decoding experiments
Amateur Radio Meetup: P25 Trunked Radio

Receiving Shortwave Radiograms with an RTL-SDR and MultiPSK

Shortwave Radiogram's are digital broadcasts of images, text and sometimes HTML files that are regularly broadcast on two shortwave radio stations, WRMI in Florida and WINB in Pennsylvania. The transmissions are produced and presented by Dr. Kim Andrew Elliott, and a schedule can be found on the Shortwave Radiogram website.

Over on his blog Jeremy Clark has been experimenting with receiving shortwave radiograms with an RTL-SDR and upconverter. To do this he notes the transmission schedule on the shortwave radiogram website, and uses SDR# and MultiPSK in MFSK mode to receive and decode the data. Jeremy's post explains the MFSK transmission mode and shows a few examples of radiograms that he's received including a video posted below showing live reception and decoding.

RTL-SDR for Shortwave Radiogram

Controlling a Wireless Ceiling Fan with an RTL-SDR and RPiTX on a Raspberry Pi

Over on YouTube River's Educational Channel has uploaded a new video showing how he uses a Raspberry Pi to control a ceiling fan via it's wireless control signal. Back in January we posted about River's first video where he shows him using and RTL-SDR and Universal Radio Hacker (URH) to reverse engineer the control signal.

In this new video River uses the RPiTX software to generate the control signal without requiring any additional transmit hardware. He first explains how RPiTX can generate an arbitrary signal from a square wave and talks a bit about the harmonics this creates. To reduce harmonics he adds a simple low pass filter to the GPIO output.

Next to control the fan he uses the "sendook" program that is included with RPiTX to transmit the binary control string that he reverse engineered in his original video. Finally he creates a simple web server so that he can control his ceiling fans via his phone and integrate it into his smart home.

Abusing Raspberry Pi GPIO pins as a radio transmitter to control my ceiling fan

Adding an RTL-SDR Antenna Port to a Pinetab Linux Tablet

The Pinetab is a US$99.99 open source Ubuntu Linux Tablet based on a low power Pine64 singe board computer. The Pinetab can optionally support an internal RTL-SDR, which is essentially just a standard RTL-SDR PCB connected to the single board computer inside the tablet enclosure.

Over on YouTube channel Privacy & Tech Tips has uploaded a video where he takes the Pinetab apart and adds an external antenna port, allowing for external antennas to be connected. In the video we get a good look at the internals of the Pinetab, and after installing the external antenna port he shows us the Pinetab receiving a LoRa signal.

Opening Pinetab (Linux Tablet) back cover (+show tips for safer opening) on video and show how you can add an external threaded antenna port for your internal SDR. It makes for an amazingly compact SDR kit and smaller antennas like LoRa fit right inside the keyboard/tablet/laptop stand. Larger antennas such as a dipole, the antenna cord fits along the case/stand perfectly.

I show how to open the Pinetab safely, and install an external threaded antenna port. After this I take a Heltec LoRa ESP32 I have had laying around and use it to demo GQRX on the screen. I show LoRa packets coming over the radio waves at 915MHz. Series on SDR using Pinetab/Pinephone/Pine64 hardware. Linux makes for an amazing platform where the tools at hand leave the limits to what you can do to the power of your imagination.

Opening Pinetab + Add SDR Modification!

Frugal Radio: Monitoring Aviation Communications Part One

Rob from Frugal Radio has recently started a new YouTube series all about monitoring aviation communications. In his first video Rob gives an overview on what can be aviation signals can monitored and recommends a few hardware scanners as well as software defined radios for monitoring.

This is an introductory video to my new series aimed about monitoring aviation communications. Throughout the series we will talk about:

  • Civil Airband (aka VHF airband)
  • Military Airband (aka UHF airband)
  • HF Aeronautical communications
  • Decoding aircraft data on HF and VHF
  • Decoding CPDLC transmissions and much more!
  • Good frequency scanners to use, like the Uniden BC125AT and BCT-15X
  • Recommended Software Defined Radios (SDR)
Monitoring Aviation Communications - Part 1

SDRSharp Guide by IZ1MLL Updated

Thank you to Paolo Romani IZ1MLL for letting us know that he has updated his popular SDRSharp users guide that we posted about previously last December. The guide is available on the Airspy downloads page. SDR# (aka SDRSharp) from Airpsy.com is designed for Airspy SDRs, however it is one of the most popular SDR receiver programs that is used with RTL-SDRs as well. Paolo's guide covers all of the settings and features in SDR# as well as some third party plugins. Paolo writes:

In the last month I have completely rewritten the guide for other devices and for the latest radical changes to the software. From today, version 2.1 is available in Italian and English for all interested guys.

We note that the guide has also been translated in Spanish and Russian, although at the time of writing those translations are still only for the older guide. 

SDRSharp Guide

Analyzing Frozen Air Traffic in the Hudson Valley

Thank you to Steve Bossert (K2GOG) for submitting his article on analyzing traffic from his RTL-SDR based ADS-B receiver during the recent heavy snow storms at his location in the Hudson Valley. His graphs show a huge drop off in air traffic and ADS-B packets received during the storms.

Aside from these results, Steve's post goes on to explain how he gathers and stores these analytics and an example of using the Graphs1090 software for producing nice plots of the aircraft receive. One important tip that he mentions is to be careful when constantly logging ADS-B data to the SD card as the card can easily get corrupted over time since there are read/write cycle limits.

Air traffic graphs showing the effect of the latest snow storm on air traffic

Getting Started with Developing Plugins for SDR# on .NET 5

Recently we posted about how SDR# was updated to the latest .NET 5 framework, and this brought with it a new plugin SDK for developers. If you're wanting to get started with plugin development, Petri-Veikko Alajärvi (OH1GIU) has uploaded a tutorial showing how to get started with the free Visual Studio 2019 Community IDE. His post shows how to create a new project, how to add references to the SDRSharp plugin files and how to set up and test a basic GUI via an RDS information display example.

Creating a new SDR# Plugin with the .NET5 Plugin SDK