Thank you to Adrian for submitting his video about using the Android App called QRadioLink and an RTL-SDR to decode digital amateur radio voice transmissions. Adrian writes that in the video the RTL-SDR connects to the Android phone with a USB OTG cable and uses a sample rate of 1 MSPS. He also writes the following about QRadioLink:
QRadioLink is a building platform which allows experimenting with VHF-UHF SDR transceivers using different modulation schemes for digital data transmissions. So far digital voice and text transmission is supported, using either a narrow band modem and Codec2 or a high bandwidth modem and Opus. Supported hardware includes the RTL-SDR, Ettus USRP, HackRF, BladeRF and in general all devices supported by libgnuradio-osmosdr.
QRadioLink running on Android (Debian chroot) with RTL-SDR
Over on YouTube Mike from the SDRplay team has created a tutorial video that shows how to use the SDRuno EXTIO edition. SDRuno is the official software of the SDRplay line of products and can be freely downloaded from the SDRplay website. The EXTIO edition allows other non-SDRplay SDR units to freely be used with SDRuno. The only restrictions are that the maximum bandwidth is artificially restricted to 2.5 MHz and some DSP filters are missing.
In the video Mike shows how to set up the SDRuno workspace to work with an RTL-SDR dongle and demos reception of some signals. Note that the EXTIO dll file for the RTL-SDR mentioned in the video is the same one required for HDSDR, and can be downloaded from the dll table on the HDSDR website.
If you’re interested in more, Mike has a full SDRuno tutorial series available on the SDRplay YouTube channel which mostly focuses on usage with the SDRplay units, but could be applicable to the EXTIO version as well.
SDRuno EXT/IO Edition for a range of SDRs and dongles
Thanks to Juan Moreno for letting us know that his online MOOC (massive open online course) on RTL-SDR is starting on September 25. The course is presented by Juan and three of his colleagues from the Technical University of Madrid. It will focus on SDR 101 knowledge such as digital signal processing with the aide of an RTL-SDR to help with practical learning. In their video they also mention that MATLAB and Simulink will be required and used for most of the course, so it will probably be a fairly technical beginners course at a University level of learning. Their description of the course reads:
SDR is a reality around us. It is present in a lot of systems everywhere and is a versatile technology which can be used for many things (not only academics and industrial). The purpose of this course is to introduce students into general-purpose SDR tools. The SDR hardware platform chosen for this course is the RTL-SDR. It is worldwide available, it’s cheap ($15) and there is a lot of help in the Internet. But, as far as we know, there is no other MOOC focused on an introduction to SDR as this MOOC. Here we will not only learn about SDR but also a lot of related areas like antennas, digital signal processing, radio frequency and communication electronics.
The website and registration forms seem to all be in Spanish or Portuguese, but the course will be presented in entirely in English. Google Translate can easily be used to help with the signup process. The course is completely free and students that complete 75% of assignments will receive a free participation certificate. A more official accomplishment certificate can be obtained for a 50 Euros.
Over on YouTube user Fuzz has uploaded a video showing his solar powered NOAA weather satellite receiver.
The system is based on a Raspberry Pi connected to an RTL-SDR.com dongle. The front-end input of the RTL-SDR dongle consists of an LNA and FM reject filter, and this is all connected up to a QFH antenna in his front yard. The electronics are completely solar powered, with the solar system consisting of solar panel, solar controller and four 12v batteries used for energy storage. A 12V to 5V step down converter is used to power the Raspberry Pi, with the 12V LNA being powered directly by the batteries. The system is able to be accessed remotely via the Raspberry Pi’s WiFi connection.
In 2015, artist Ai Weiwei was bugged in his home, presumably by government actors. This situation raised our awareness on the lack of research in our community about operating and detecting spying microphones. Our biggest concern was that most of the knowledge came from fictional movies. Therefore, we performed a deep study on the state-of-the-art of microphone bugs, their characteristics, features and pitfalls. It included real life experiments trying to bug ourselves and trying to detect the hidden mics. Given the lack of open detection tools, we developed a free software SDR-based program, called Salamandra, to detect an locate hidden microphones in a room. After more than 120 experiments we concluded that placing mics correctly and listening is not an easy task, but it has a huge payoff when it works. Also, most mics can be detected easily with the correct tools (with some exceptions on GSM mics). In our experiments the average time to locate the mics in a room was 15 minutes. Locating mics is the novel feature of Salamandra, which is released to the public with this work. We hope that our study raises awareness on the possibility of being bugged by a powerful actor and the countermeasure tools available for our protection.
The paper first outlines the history of microphone bugs and tries to dispel some of the myths about them which originate from movies and other fictional sources. They then perform a survery of the current state-of-the-art microphone bugging techniques, and later go on to discuss the development of Salamandra and some experiments that they performed with it.
In their experiments they show that the Salamandra software and RTL-SDR is able to outperform a commercial bug detector. They also performed several real world simulations where one researcher would hide a bug in a room, and then another would have to use Salamandra to determine if a bug was present, and then locate it using the location feature of Salamandra. They concluded that Salamandra was a very useful tool as they were able to detect the location of the bugs in under 40 minutes in 4/5 tests.
An example waterfall of a microphone bug transmitting and being received with an RTL-SDRLocation of a hidden bug in one of their tests.
Recently the Outernet project transitioned from using RTL-SDR dongles and C.H.I.P single board computers to using their Dreamcatcher board, which is an RTL-SDR and computing board all in one. In between the transition they also produced a number of ‘SDRx’ dongles. These were custom RTL-SDR dongles with a built in L-band LNA and filter. As they no longer need the SDRx they have them on clearance at their store.
The clearance price is $15 USD which is an excellent deal. Remember though, that the SDRx is limited in frequency range – it is designed for receiving L-band satellites between 1525 – 1559 MHz and the filter will cut off all other frequencies.
The Outernet SDRx on Clearance
Just add a simple L-band tuned antenna to the port and you should be able to receive Inmarsat and a signal like STD-C, AERO or the Outernet signal. A suitable antenna might be a homebrew patch, helix, cooking pot antenna or even a small tuned V-dipole antenna can work for the stronger AERO signals.
We also see that the price of their L-band Outernet active ceramic patch antenna has been dropped down slightly to $25 USD. This antenna is bias tee powered and can be used with a V3 dongle or their Dreamcatcher hardware. The Dreamcatcher itself is also now reduced in price to $59 USD.
We have a review of the Dreamcatcher and active ceramic patch antenna available here.
Outernet Dreamcatcher and L-Band Active Ceramic Patch
We also now list Outernet products in our store. These are commission sales so we receive a little bit per purchase which supports the blog, and the items are shipped by Outernet within the USA.
If you were unaware, Outernet is a free L-band based satellite service that provides content such as news, weather data, APRS repeats and more. Currently you can get about 20MB of data a day. Outernet receivers are also all based around the RTL-SDR, allowing for very cheap receivers to be built
Over on YouTube user Fuzz has uploaded a short video showing his “Ham Radio Go Box”. This is a plastic box containing inside many pieces of mounted equipment, all hooked up and ready to go. Inside he has a Raspberry Pi connected to a 7-inch touch screen and RTL-SDR Blog V3 dongle. The Raspberry Pi is used for satellite tracking and for driving an external bluetooth speaker. He also has inside a Baofeng BTECH tri-band radio which connects to an external speaker. The box also seems to have battery charging via an external solar panel.
Ham Radio Go Box With Raspberry Pi And Bluetooth speaker and SDR
Voice inversion scrambling is a simple and old security method used on analog radios to try and obscure conversations from being listened in on by people with scanners. It works simply by by moving the low frequencies higher and the high frequencies lower, or in other words inverting the audio. A descrambler is then required to recover the true audio, otherwise you will only hear garbled audio. Voice inversion provides little real security, as it is very simply to descramble, and many scanner radios already have descrambling features built in. These days most secure communications are digital and encrypted, but voice inversion scrambling is still available on many analog radios, and could still be in use by some users looking for protection against casual eavesdroppers.
Oona Räisänen (aka windytan) has recently released a simple program called ‘deinvert’ over on GitHub. This program is a descrambler that reads in a scrambled wav file and outputs a descrambled audio file. The audio file could be easily recorded with an RTL-SDR and rtl_fm, or a similar SDR.
