Category: Applications

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

Building an 11.2 GHz Radio Telescope with an Airspy and 1.2m TV Satellite Dish

In the past we've posted several times about how 1.42 GHz Hydrogen Line amateur radio telescopes used with RTL-SDRs or other SDRs for Hydrogen line observations of the galaxy. Recently Hackaday ran a post highlighting a project from "PhysicsOpenLab" describing an 11.2 GHz radio telescope that uses an Airspy SDR as the receiver.

Celestial bodies emit radio waves all across the radio spectrum and typically observations can be made anywhere between 20 MHz to 20 GHz. Choosing an optimal frequency it is a tradeoff between antenna size, directivity and avoiding man made noise. For these reasons, observations at 10-12 GHz are most suitable for amateur radio telescopes.

The posts by PhysicsOpenLab are split into two. The first post highlights the hardware used which includes a 1.2m prime focus dish, and 11.2 GHz TV LNB, a wideband amplifier, a SAW filter, a bias tee, and the Airspy SDR. The LNB converts the 11.2 GHz signal down to 1.4 GHz which can be received by the Airspy. Once at 1.4 GHz it's possible then to use existing commercial filters and amplifiers designed for Hydrogen line observations.

The second post explains the GNU Radio based software implementation and the mathematical equations required to understand the gathered data. Finally in this post they also graph some results gathered during a solar and lunar transit.

Finally they note that even a 1.2m dish is quite small for a radio telescopic, but it may be possible to detect the emissions from the Milky Way and other celestial radio sources such as nebulae like Cassiopeia A, Taurus A and Cygnus A a radio galaxy.

A 11.2 GHz 1.2m Amateur Radio Telescope with GNU Radio and Airspy