Category: Applications

Information about Receiving the GOES-13 Weather Satellite (Europe Coverage with 1.8m Dish)

For some time now many weather satellite enthusiasts have enjoyed the ability to relatively easily receive live high resolution images directly from the GOES-16, GOES-17 and GK-2A geostationary satellites (tutorial here). However, while much of the world can see at least one of these satellites, European's have been left out.

What may be of some interest to Europeans is that the older GOES-13 (aka EWS-G1) satellite was repositioned in February 2020, and it can now be received in Europe (as well as Africa, the Middle East, Asia, Russia and West Australia) until at least 2024 when it will be replaced.

The important catch however is that GOES-13 is not broadcasting the same easy to receive LRIT/HRIT signals that the other satellites use. The signal is still in the L-Band at 1685.7 MHz, however it is called "GVAR" and it is much weaker and uses 5 MHz of bandwidth. For GOES 16/17 and GK-2A a 1m WiFi grid dish, LNA and RTL-SDR was sufficient, but for GOES-13 you'll need a much larger 1.8m dish, and a wider band SDR like an Airspy. The big dish requirement significantly increases the reception challenge.

We also note that the decoder is being developed by @aang254 and u/Xerbot and it is not yet publicly released. However, they do intend to release it soon. Update:

Over on his blog Carl Reinemann has been collecting some useful information about GOES-13 reception. Over on Reddit u/derekcz has also created a post with some useful information. We've also been talking to @ZSztanga in Poland who has been testing this satellite out, he wrote:

My hardware is: 180cm prime focus dish, with a custom cantenna (120mm diameter). I'm using the SAWBIRD GOES LNA. I will be switching to the + version, because the setup is still lacking a few db SNR. The SDR is the one I use for HRPT: the airspy mini

I found that the USB connection on the airspy generates a lot of noise, so I removed the USB cable, by moving the airspy to the laptop. I use 2m of CNT-400 coax and it works much better now. I get about 2 db SNR more. Thought you might find it interesting.

@ZSztanga's GOES-13 Reception Setup, with 1.8m dish.

We note that there is some interesting differences with GOES-13 images. Since the image is less processed, it is higher resolution (a full resolution image can be found on this Reddit post), as well as not cropped, meaning that the Earth's atmosphere is visible. Please also follow @ZSztang on Twitter for more images.

Hermes and Red Pitaya now Supported in OpenWebRX

Thank you to Stefan Dambeck (DC7DS) for submitting news about OpenWebRX adding support for Hermes HPSDR compatible SDRs. Hermes is a single board version of the open source high performance SDR (HPSDR) design. There are several compatible Hermes designs including the newer Hermes-Lite 2 . The Red Pitaya is an open source electronics laboratory instrument, but custom software can be installed allowing it to function as an HPSDR type SDR. OpenWebRX is software which allows you to access your SDR remotely via the internet or local network through a web browser. Stefan notes:

I built a test setup today using a Red Pitaya 125-14 SDR in HPSDR mode, and this is now also supported, see screenshot.

At the moment, only one receive stream is supported, for the red pitaya with 192KHz bandwidth.

The Red Pitaya running in OpenWebRX

DF Aggregator: New Software for Networked Radio Direction Finding with KerberosSDR

Over on GitHub Corey (ckoval7) has released a new open source radio direction program called "DF Aggregator". This software is able to receive bearings and locations from multiple remotely networked KerberosSDRs, and display them on a map.

If you weren't already aware KerberosSDR is our 4-channel phase coherent capable RTL-SDR unit that we previously crowdfunded back in 2018. With a 4-channel phase coherent RTL-SDR interesting applications like radio direction finding (RDF), passive radar and beam forming become possible. It can also be used as four separate RTL-SDRs for multichannel monitoring.

A single KerberosSDR combined with an antenna array is able to determine a bearing towards a signal source. By using multiple KerberosSDR units spread over a large area it is possible to triangulate the location of a transmitter and display it on a map. Corey's software uses a modified branch of our open source KerberosSDR code in order to generate a modified XML page that the mapping software polls for updated data. Some instructions on it's use are available on our forums and on the GitHub.

The image below shows three KerberosSDR stations on the map, and two transmitter locations that have been triangulated using the bearings from the three distributed KerberosSDR units. 

Alternative direction finding mapping software includes our Android App (mostly for mobile vehicular use), and RDF Mapper with our adapter code.

DF Aggregator: KerberosSDR Direction Finding Mapping Software

A 3D Printed Automatically Adjusting Linear Antenna Array for KerberosSDR Radio Direction Finding

Over on GitLab Josh Conway has released a design for an automatically adjusting antenna array which can be used with radio direction finding capable SDRs like our KerberosSDR. KerberosSDR is a SDR consisting of four RTL-SDRs connected to the same oscillator, a USB hub, a built in noise source and calibration hardware which allows software to use the four RTL-SDRs coherently. Coherent operation of SDRs enables interesting applications such as radio direction finding, passive radar and beam forming.  

With coherent antenna array based direction finding, the optimal spacing between the antenna elements is proportional to the wavelength of the frequency being received. If you want to do RF direction finding on different frequencies, either multiple antenna arrays with different element spacings, or manually adjusting the antenna array with each frequency change is required.

Josh's design automates this problem with an antenna array that can adjust the spacing automatically. The design puts the antennas on an extending pantograph arm whose length is controlled via a threaded rod connected to a stepper motor. An Arduino microcontroller controls the stepper, thus allowing the spacing to be adjusted automatically. 

A Pantograph Antenna Array for Direction Finding

A full description of the build is provided in the document on GitLab titled "provisional_patent_application.pdf". From Twitter it appears that Josh (@CrankyLinuxUser) was unable to secure a patent for this design, so he has released the design for free under AGLP3. Most of the parts are 3D printed, and the CAD stl files all appear to be available on the GitLab. The Arduino microcontroller firmware is also available.

Thank you to Josh for releasing this design!

Pantograph Antenna Array for Direction Finding

Radio Spectrum Analysis in Virtual Reality with an RTL-SDR and Google Cardboard

Thank you to José Carlos Rueda for submitting his project called "a-radio: a web virtual reality radio power spectrum analyzer". The idea behind the project is to first use an RTL-SDR together with rtl_power and heatmap.py to generate a heatmap image of the RF spectrum. This image is then projected into a 3D 360 degree view and hosted on a web server via José's script for the a-frame VR web framework, allowing the heatmap to be viewed with a virtual reality (VR) smartphone headset. José' recommends using a cheap VR headset like Google Cardboard which can be used with your Android smartphone. 

José notes that the project is just a proof of concept, but he hopes to inspire future work around the combination of RF and VR.

Virtual Reality Visualization of an RF Spectrum Heatmap.

Andreas Spiess Tracks Weather Balloons with a TTGO LoRa Board and RTL-SDR

Earlier in August we posted about radiosondy.info and the MySondy radiosonde receiver. Radiosondy.info is an internet service that aggregates radiosonde weather balloon data received and decoded by RTL-SDR users all over the world. MySondy is a cheap TTGO LoRa receiver that is modified with custom firmware and combined with a companion Android app in order to create a portable radiosonde receiver. A radiosonde is a small sensor and radio package normally attached to a weather balloon. Meteorological agencies around the world typically launch two balloons a day from several locations to gather data for weather prediction. With cheap hardware like an RTL-SDR and the right decoding software it is possible to receive weather and GPS data from the weather balloons launched in your area. 

Over on his popular YouTube channel, Andreas Spiess "the guy with the Swiss accent" has uploaded a video featuring the RadioSondy and the MySondy receiver projects. In the video Andreas first explains what a radiosonde is, and who launches them. He goes on to show the RadioSondy website and how to track balloons on it. He then shows the portable MySondy receiver for tracking radiosondes, before finally showing how to set up a permanent fixed ground station with RTL-SDR and Raspberry Pi for contributing to the RadioSondy aggregation website.

In amongst the demonstrations he also goes on several hunts for weather balloons that have landed near him, ultimately recovering two radiosondes and one intact balloon. The radiosondes were initially tracked with the RadioSondy fixed RTL-SDR ground stations, then when in the vicinity of the landed balloon pinpointed and found with the MySondy hardware.

#360 Tracking and Chasing Weather Balloons with TTGO LoRa Board and Raspberry Pi. Fun and Adventure

Frugal Radio: SDR Guide Ep 6 – Trunk Tracking Public Safety Systems with UniTrunker and SDRTrunk

In this episode of Frugal Radio's ongoing SDR Guide videos Rob demonstrates how he uses Unitrunker and SDR Trunk with SDRs like an RTL-SDR to monitor Public Safety networks in his area. Rob writes:

This is a video demonstrating how I use UniTrunker and SDRTrunk with Software Defined Radios to monitor multiple Public Safety networks in my area.

There is some information on how trunked systems work, and you can hear how my SDRs produce better P25 audio on a Simulcast (LSM) system than some scanners.

I use a couple of RTL-SDR v3s and an Airspy R2 in this episode.

2020 SDR Guide Ep 6 : Trunk tracking Public Safety systems with UniTrunker and SDRTrunk

RF Fingerprinting ADS-B Signals for Security

At this years ICNP 2020 IEEE conference a paper titled "Real-World ADS-B signal recognition based on Radio Frequency Fingerprinting" (pdf file) was presented by researchers from Harbin Engineering University in China. The idea presented in the paper is to use RF "fingerprinting" techniques to uniquely identify and confirm that the ADS-B signal originates from the correct aircraft source.

RF fingerprinting works on the premise that every transmitter has small manufacturing variances that result in slightly different signals be transmitted, resulting in a unique "fingerprint" that can be traced to a particular transmitter. The idea here is to use these fingerprints to ensure that a known aircraft is indeed transmitting an ADS-B signal and the signal is not being transmitted from a fake spoofer. ADS-B is completely unencrypted and not authenticated, so spoofing of ADS-B signals may be a real security threat.

In the teams research they use an RTL-SDR to collect ADS-B signals from five different aircraft. They then use that data to create "Contour Stellar Images" and train a deep learning neural network which after training accurately identifies which aircraft a signal comes from.

Aircraft ADS-B Fingerprinting

In previous posts we've seen the idea of fingerprinting used by Disney research and others to identify electronic devices, to authenticate RF IoT devices and to identify handheld transmitters via CTCSS fingerprints.