Category: RTL-SDR

KerberosSDR: Tracking a Weather Balloon Radiosonde with Radio Direction Finding

The KerberosSDR is our 4-channel phase coherent capable RTL-SDR unit that we previously successfully crowdfunded back in 2018.  With a 4-channel phase coherent RTL-SDR interesting applications like radio direction finding, passive radar and beam forming become possible. It can also be used as 4 separate RTL-SDRs for multichannel monitoring.

KerberosSDR can be purchased from our partner store at https://othernet.is/products/kerberossdr-4x-coherent-rtl-sdr.

In one of our latest tests we've been able to track a weather balloon radiosonde via the direction finding ability of KerberosSDR. These balloons are launched twice daily by meteorological agencies around the world, and the radiosonde carried by the balloon transmits an RS-41 signal continuously throughout it's flight sending back telemetry such as weather information and GPS coordinates. The KerberosSDR tracks the bearing towards the balloon using only the raw signal - it does not decode. Having the actual GPS location from the RS41 data allows us to compare and confirm that the KerberosSDR is indeed tracking the bearing of the balloon.

In this test we used the excellent 4-element dipole array made by Arrow Antennas. In particular we used the 406 MHz element version as the RS-41 signal is broadcast at 403 MHz. The antenna array is mounted on the roof, the KerberosSDR is in the attic connected to a Raspberry Pi 4. Our KerberosSDR Android app is used to plot the bearings. A separate RTL-SDR running on the video recording PC is connected to it's own antenna and is used to receive and decode the RS41 signal. The free software RS41 Tracker is used to decode and map the balloon for location confirmation. 

We are currently using the latest beta code in development (unreleased at the time of this post - it will be released within 1 to 2 months) which handles non-continuous intermittent signals better.

Arrow Antennas 4-Element Dipole Array Mounted on Roof

The short video below shows a timelapse of the RS41 decoder tracking a balloon which circled the south of our KerberosSDR. The red line indicates the zero degree direction of the antenna array, while the blue line indicates the estimated direction of the balloon determined via the MUSIC radio direction finding technique.

The GPS balloon map from RS41 tracker is overlayed on top of the KerberosSDR Android app map for clarity via video editing. We can see that it mostly tracks the balloon to within a few degrees. When the blue bearing line diverges this is due to the balloon's line of sight path to the antennas being obscured by terrain, buildings or trees. When this is the case a multipath signal reflecting off surrounding hills tends to become dominant.

In the second short video below the weather balloon tracked northwards. Towards the north, north west and north east we have antenna obstructions in the form of rising terrain, houses and hills, so the overall accuracy is poorer. However, it still tracks within a few degrees most of the time.

Finally the YouTube video below shows the same as the above, but in the second half includes the full screen including the KerberosSDR DoA graphs and SDR# waterfall showing signal strength.

KerberosSDR Tracking a Weather Balloon Radiosonde with Radio Direction Finding

In the future we hope to test with two or more KerberosSDR units producing multiple bearing lines on RDFMapper, hopefully resulting in cross points that can be used to estimate the actual location of the balloon.

A Handheld SciFi Scanner Box with RTL-SDR and Thermal Camera

Over on his YouTube channel "saveitforparts" has been working on creating a handheld scanner/sensor box on a budget. This is a simple and fun build which is attempting to create something like a real life Star Trek scifi tricorder that you might imagine taking with you to analyze systems on another planet. The box embeds a Raspberry Pi, USB hub, battery pack, RTL-SDR and thermal camera inside. In the video he shows how everything fits into the box and gives a quick demo of the RTL-SDR and thermal camera in action. In the future he plans to add more sensors as well.

Handheld Scanning Device with Raspberry Pi - Part 2

BSides Talk: It’s 2020, so why am I still able to read your pager traffic?

At the BSides OK 2020 virtual conference Cameron Mac Millan recently presented a talk titled "It’s 2020, so why am I still able to read your pager traffic?". On this blog we have posted numerous times about privacy breaches stemming from insecure wireless pager traffic. Anyone with a radio or SDR can receive and decode pager messages, and this has been known and done since the 1980's. Cameron's talk explains how paging systems work, who are the modern users of pagers, how to capture and decode pager messages and how to best log and filter through messages. He goes on to describe a number of major pager security breaches that he's personally seen. The talk preview reads:

This talk explores why pagers remain a potential threat vector in many environments despite the technology being 40 years old. This is not a the-sky-is-falling presentation: everything from paging history to how simple it is to decode pager traffic (and the associated risks) is covered without FUD.

I enjoy poking things with sticks and turn over rocks to see what crawls out from under them. One of my interests is seeing how technologies believed to be obsolete can still pose a problem for security today, and do that from the perspective of a 20-year career in infosec. When not creating tomorrow’s problems with yesterday’s technology, I can usually be found wrenching on unusual cars.

It’s 2020, so why am I still able to read your pager traffic? - Cameron Mac Millan - BSidesOK 2020

TechMinds: OpenWebRX Feature Overview And Raspberry Pi Setup

Over on YouTube TechMinds has posted his latest video which shows an overview of the features available in OpenWebRX, and also how to set it up on a Raspberry Pi. OpenWebRX is software which allows you to access your SDR remotely via the internet or local network through a web browser. All major SDRs are supported including RTL-SDRs. The software includes a waterfall display, all the standard demodulators, as well as several digital decoders for DMR, YSF, NXDN, D-Star, POCSAG, APRS, FT8, FT4, WSPR, JT65 and JT9.

In the video TechMinds first demonstrates OpenWebRX in action, showing reception of HF SSB amateur radio signals, decoding FT8 and plotting received grids on a map, decoding and plotting APRS on a map and decoding YSF/DSTAR/DMR digital voice. After this demonstration he goes on to show how to set up the OpenWebRX server on a Raspberry Pi via the installation image.

OpenWebRX Feature Overview And Raspberry Pi Setup

Sanchez: Create False Colour Images from GOES/Himawari/GK-2A Infrared

With an RTL-SDR, an appropriate satellite antenna and LNA it is possible to receive visible light images from geostationary satellites such as GOES/Himawari and GK-2A. However, in a 24 hour cycle there will only be one or two images that show the Earth fully illuminated by the sun. The rest of the day parts or all of the Earth will be dark with not even clouds visible. To get around this the satellites also use an Infrared (IR) camera which can see clouds at all times. However, these images are greyscale and not very visually appealing.

To fix this aesthetic issue there is now a recently released multiplatform tool called "Sanchez" which will combine a high resolution underlay image with the greyscale IR image in order to create a more beautiful image. The software is command line based and can run on a batch of collected images.

False colour satellite images made by Sanchez

Testing the Electrosense Up/Downconverter Expansion Board For 0 – 6 GHz

The Electrosense network is an open source project aiming to deploy radio spectrum sensors worldwide. The idea is to help analyze and understand radio spectrum usage across the globe. Each sensor consists of an RTL-SDR, Raspberry Pi and an optional downconverter to receive the higher bands. If you're interested we wrote an overview of the project in a previous post. 

Recently we received a sample of their Up/Downconverter expansion board which is used to expand the frequency range of the RTL-SDR to 0 MHz to 6 GHz. The converter board is entirely open source with the design files available on GitHub. The team note that they are also working on a V2 version which will be cheaper and smaller. The schematic and Firmware for the V2 is also available right now, but it is still under early testing and may change.

The board is not for sale, however you can apply to be considered for a free unit if you want to host your own Electrosense node and meet their criteria. If you do not you can still produce the board yourself. The team mention that the design is easily hand soldered, but there are a few difficult LGA components like the PLL, crystals and mixer which require a heat gun to solder. A the same time they also note that it is possible to get PCB manufacture and SMT assembly done for you for dirt cheap by PCB prototype companies like JLC PCB. 

The Expansion Up/Downconverter Board

The converter board has 4-input SMA ports (only 3 are used) and one output port which connects to the RTL-SDR. The first input port is for the HF antenna input. This input connects to the circuit which converts 0 - 30 MHz into a higher frequency which can be received by the RTL-SDR. The second port is simply a pass through for the standard 24 MHz - 1.766 GHz range of a normal SDR. The third port is unused, and the fourth port connects the antenna to the downconverter circuit which allows us to receive from 1.766 GHz to 6 GHz.

The Electrosense Converter Board

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TechMinds: Using Public Online SDRs without SDR Hardware

This weeks video on the TechMinds channel explores the various online web SDRs that are available to access for free. Accessing these online SDRs does not require any hardware apart from a PC and internet connection, although of course you are then receiving signals from a different location to yourself. 

In the video he shows how to access the SDR# Spy Server Network which mostly consists of Airpsy and RTL-SDR units, the SDR-Console V3 Server network which consists of a wide array of different SDRs, the browser based WebSDR network which is mostly soundcard based SDRs but also RTL-SDR and other SDRs, and finally the KiwiSDR network which is made up of KiwiSDRs.

Using Software Defined Radio Without SDR Hardware - WebSDR

SignalsEverywhere: Setting up a Broadcastify Feed with SDRTrunk

In her last video Sarah from the SignalsEverywhere YouTube channel showed us how to set up SDRTrunk for reception of digital P25 Police and other services with two RTL-SDR dongles. On this weeks episode Sarah shows us how to set up Broadcastify with SDRTrunk. Broadcastify is a an online service that allows you to stream audio from your SDR or scanner radio to their website for anyone to listen to. We note that sharing audio or some talkgroups may not be legal in all countries so please do your research first.

In the video Sarah shows the full setup process involving setting up a Broadcastify account, creating an alias list, adding talkgroups to share and finally setting up the Icecast server for streaming to the Broadcastify servers.

SDRTrunk Broadcastify Feed Tutorial