The South Indian SDR User Group (SI-SDR-UG) have recently held their fourth live stream conference. This conference included some interesting talks such as:
"Introduction to GNU Radio Series, Part 2" by Neel Pandeya
"Silice, a Language for Hardcoding Algorithms into FPGA Hardware" by Dr.Sylvain Lefebvre
"RF Geo-Location for Everyone" by Corey Koval
"Overview of Wireless Channels, Part 1" by Aditya Arun Kumar
In particular we were interested in Corey's talk which starts at 1:27:40 and talks about DF-Aggregator, an open source mapping program he's written for KerberosSDR, KrakenSDR and any other radio direction finding hardware that can be adapted to the software. In the talk Corey explains what DF-Aggregator is and how the clustering algorithm works.
South Indian SDR User Group (SI-SDR-UG) Live Stream Event-4
STD-C is a marine satellite service that broadcasts messages that typically contain text information such as search and rescue (SAR) and coast guard messages as well as news, weather and incident reports. With the right software, an RTL-SDR and an appropriate L-Band satellite antenna like our 'Active L-Band 1525 - 1660 Inmarsat to Iridium Patch Antenna Set' these signals can be received and decoded.
The stdcdec software provides a way for command line only systems to receive and view STD-C data. In his video Aaron shows an example setup that uses SigDigger to determine the audio frequency offset, and receive the audio which is then passed to the stdcdec software. We note that SigDigger is a GUI based program but could probably be replaced with another CLI based program, in order to run on a headless system (as long as the tuning and audio center freq is determined before hand). Aaron is hoping to explore solutions for this in the future.
Thank you to Sasha for submitting news about the release of their latest application called "apt_color". The most popular application for decoding APT weather satellite images from NOAA polar orbiting satellites is WXtoIMG. However, WXtoIMG is closed source and is abandonware. There are APT decoder alternatives, however unlike WXtoIMG most other open source APT decoders only provide black and white images, and do not have a false color feature.
The apt_color application can be used to turn black and white APT images received from NOAA satellites into false color images. Sasha writes:
I am working on an APT false color application here. The application is still in the very, very, early stages but still seems to produce good results. It does not need to rely on any overlays, it simply works off the data you give it - the original decoded image data. I will attach some results. NOAA-18 seems to be the best suited spacecraft for this program.
apt_color: Turn black and white NOAA images into false colorapt_color: Examples
Researchers from Carnegie Mellon University have recently presented a paper detailing how they combined noisy signals from multiple passes of low earth orbit (LEO) satellites NOAA 15, NOAA 18 and NOAA 19 in order to create a higher quality image. For a receiver they used a low cost RTL-SDR Blog V3 mounted indoors with a whip antenna.
In a normal setup, weather satellite images from NOAA LEO weather satellites can be received with an RTL-SDR, computing device and an appropriate outdoor mounted antenna that has a good view of the sky. If the antenna is not suited for satellite reception, and/or is mounted indoors, at best only poor quality very noisy images can be received.
The researchers demonstrate that it is possible to combine noisy images received over time, and from different satellites in order to generate a higher quality image. The challenge is that the different satellites and different receiving times will all produce different images, because the satellites will be at a different location in the sky each pass. They note that simply transforming the images in the image domain would not work very well for highly noisy images, so instead they have devised a method to transform the images in the RF domain. The RF signals are then coherently combined before being demodulated into an image.
The results show that 10 noisy satellite images from the indoor system are comparable to one from a comparison outdoor system. However, they note some limitations in that the system assumes unchanging cloud cover during passes. In the future they hope to extend the system to cover other modulation schemes used by other low earth orbit satellites in order to increase the number of usable satellites.
Selfiestick: Combining noisy images from multiple NOAA satellites received by an indoor RTL-SDR system.
Over on the TechMinds YouTube channel Matt has been experimenting with using a PlutoSDR for QO-100 amateur radio satellite communications. The PlutoSDR is a low cost RX/TX capable SDR with up to 56 MHz of bandwidth and 70 MHz to 6 GHz frequency range (with mods). The PlutoSDR can suffer from frequency instability, especially when warming up, however on the latest model C/D PlutoSDRs it's possible to inject an external clock signal.
In his video experiment, Matt uses a Leo Bodnar GPSDO as an external clock source. A GPSDO is a "GPS Disciplined Oscillator", as it uses the accurate timing information found in GPS signals to create a high quality clock signal. Matt shows how to set up the GPSDO, and how to tell the PlutoSDR to use the external clock.
He goes on to show the effectiveness of the GPSDO with some transmit experiments.
Back in May 2021 we first posted about the release of MagicSDR, which is an Android and iOS SDR app that receives data from an rtl_tcp server elsewhere on your network. Apart from the RTL-SDR, MagicSDR also supports the SDRplay, LimeSDR, HiQSDR, Flex 6-seris and sound card based radios.
Recently MagicSDR programmer Vlad wanted to share a new feature in MagicSDR that allows users to stream audio over UDP. He notes that this allows external data decoders such as direwolf or multimon-ng to be used. The example in the video below shows MagicSDR sending demodulated audio over UDP to multimon-ng running on the same Android device.
Decoding Morse CW on android phone
MagicSDR sending demodulated audio over UDP to multimod-ng decoder
Back in 2020 we posted about a modified ExtIO interface which exposed advanced RTL-SDR driver settings such as decimation, manual gain and tuner bandwidth and filtering controls. These features allow users to tune filters to avoid ADC overload and to overall fine tune reception better, especially for narrowband signals. ExtIO is the driver interface used by some popular SDR programs like HDSDR.
DG2YCB improved version adds the following features:
Auto-Q: The RTLSDR stick automatically switches to direct sampling (Q channel) for frequencies below 24.5 MHz and direct sampling is automatically disabled when tuned to any frequencies above 24.5 MHz.
My ExtIO_RTLTCP_improved.dll drivers set the chip AGC to ON, which brings you a better RX sensitivity than the original version.
My ExtIO_RTLTCP_improved.dll drivers are available in the following versions:
ExtIO_RTTCP_improved1.dll uses autoGain for the tuner gain.
ExtIO_RTTCP_improved2.dll uses optimized manual gain settings for the tuner gain, which shall prevent that the RTLSDR stick is overdriven on VHF / UHF frequencies.
ExtIO_RTTCP_improved3.dll has Auto-Q as well as the optimized gain settings profile but has a more sophisticated GUI, so that you can adjust more parameters manually. (Currently available as beta version.)
This ExtIO also allows users to connect to an RTL-SDR when software like HDSDR is run on Linux via an emulator such as WINE.
Over on the TechMinds YouTube channel Matt has uploaded a video demonstrating the use of the ISM Packet Decoder plugin for SDR# which was released a few months ago. The plugin authors website also contains more information about the installation and features of plugin.
The plugin makes use of the well known rtl_433 software behind the scenes, which is a command line based RTL-SDR compatible decoder for various wireless ISM band devices such as weather stations, car keys, tire pressure sensors, doorbells and various other remote controlled devices. The plugin GUI makes using and displaying data from rtl_433 much more convenient.
