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.
Back in July 2020 we first posted about the alpha release of "SDR++" which back then was a new project by "Whatsthegeek" that was determined to bring an open source, cross platform, C++ based GUI general receiver program for various SDRs including the RTL-SDR to the community. Over the past few months the author has been working hard on updating the software, and it's look a lot more mature today. Recently he has released the following updates as mentioned on his Reddit post:
As some of you might remember, I posted back in june about my SDR++ project. During the past 6 months, I've been hard at work to make it into usable software! The versions I released in june and july were extremely buggy and unusable. All of those issues have now been fixed. It's now simple to build and install. Here's a small rundown of the features it now has:
Fully modular architecture (plugins)
Support for most SDRs through dedicated modules or SoapySDR
Both baseband and audio recording with a level meter and volume adjust
Multiple bandplans available (very easy to write your own)
Switchable waterall colormap
Low CPU usage (lower than GQRX, CubicSDR, SDRConsole and in some cases SDR#)
Full waterfall update when zooming or changing min/max level
Also, SDR++ now runs on Windows, Linux, OSX and BSD! Do note that it still has a few quirks and misses some features (see https://github.com/AlexandreRouma/SDRPlusPlus/projects/2 for the todo list) In addition to what's in the todo list, decoders for common satellites will be written very soon. They will allow decoding of Meteor and NOAA with no external software needed!
I'd like to thank Airspy, Analog Devices, SDRplay and Howard Su for sending samples of their hardware for development! Would never have been able to add support for their hardware without it!
I hope this software will be useful to the community :)
We note that over on Twitter Whatsthegeek (@ryzerth) has been releasing further updates. He notes that some of the latest code updates for SDR++ add a native RTL-SDR module including bias tee support, and that it is also now available as a package for Arch Linux users over on the user Repository. However these latest updates are not yet available as binaries on the releases page.
In a recent tweet he also demonstrates the very useful looking multi-vfo feature allowing him to decode three AERO signals with Jaero simultaneously on a single RTL-SDR dongle.
Developer @dernasherbrezon has recently released a new program called "sdr-server" which is a streaming server. Unlike the more basic rtl_tcp server, sdr-server has some more advanced features like being able to serve multiple clients a slice of the bandwidth simultaneously. When compared to SpyServer, another advanced RTL-SDR compatible streaming server, sdr-server has similar features, however, sdr-server is open source. Some of the key features include:
Share available RF bandwidth between several independent clients:
Total bandwidth can be 2016000 samples/sec at 436,600,000 hz
One client might request 48000 samples/sec at 436,700,000 hz
Another client might request 96000 samples/sec at 435,000,000 hz
Several clients can access the same band simultaneously
Output saved onto disk or streamed back via TCP socket
Output can be gzipped (by default = true)
Output will be decimated to the requested bandwidth
Clients can request overlapping RF spectrum
Rtl-sdr starts only after first client connects (i.e. saves solar power &etc). Stops only when the last client disconnects
The popular SDR# (SDRSharp) software has recently been updated to version 1788, and now runs on the .NET5 SDK. Most of the upgrades are behind the scenes, but generally the new version appears to be more memory efficient and loads faster. The new version also brings more theme and layout customizations and as explained further below an improved plugin SDK for developers.
In order to install the latest version you will need to download .NET5 runtime from Microsoft which may not already be on your system. For RTL-SDR users you can then run install-rtlsdr.bat then start the software as usual.
One of the most exciting new developments is the new .NET 5 plugin SDK that is now available. This allows third party developers to easily code up plugins for SDR#. While a plugin SDK already existed before, the new version appears to make development much simpler, and also comes with a few examples to help get developers started quickly. The result is that we should start to see more plugins appearing in the future with more features.
One plugin called Scytale-C for Inmarsat STD-C channel decoding has already been updated to the new SDK. The developer notes that the plugin now works great with the SDR# "slicer" feature, which allows users to decode multiple STD-C signals within the received bandwidth at the same time.
We've also recently seen reports of Twitter users having success with running this new SDR# version on WINE under Linux. Unfortunately direct USB still doesn't work under WINE, but it would still function via SpyServer or rtl_tcp.
Thank you to Laakso Mikko a PhD student at Aalto University School of Electrical Engineering for submitting news about his research group's latest paper involving a 21-channel phase coherent RTL-SDR system. Laakso writes that he an his colleagues have built a (massive) multichannel receiver array from RTL-SDRs to use in low-budget research. The paper presented at EUSIPCO2020 can be found at IEEE, and for free on their research portal (direct pdf link). The code is also entirely open source and available on GitHub.
Phase coherent SDRs enable interesting applications such as radio direction finding (RDF), passive radar and beam forming.
We introduce a modular and affordable coherent multichannel software-defined radio (SDR) receiver and demonstrate its performance by direction-of-arrival (DOA) estimation on signals collected from a 7 X 3 element uniform rectangular array antenna, comparing the results between the full and sparse arrays. Sparse sensor arrays can reach the resolution of a fully populated array with reduced number of elements, which relaxes the required structural complexity of e.g. antenna arrays. Moreover, sparse arrays facilitate significant cost reduction since fewer expensive RF-IF front ends are needed. Results from the collected data set are analyzed with Multiple Signal Classification (MUSIC) DOA estimator. Generally, the sparse array estimates agree with the full array.
Mikko notes that his next paper on applying deep neural nets to the problem of near-field localization will be presented at this years VTC2021 conference, so we are looking forward to that paper too.
Back in March last year we first posted about the release of SATSAGEN, and program by Alberto (IU1KVL) that allowed the PlutoSDR to work as a spectrum analyzer. SATSAGEN has recently been updated to version 0.5, and it now supports the RTL-SDR, HackRF and Simple Spectrum Analyzer hardware as well.
Spectrum analyzer software allows you to monitor spectrum activity over a bandwidth much larger than what your SDR supports. It works by rapidly sweeping over multiple frequencies and stitching the spectrum slices together.
Some highlights of the new features include:
Simple Spectrum Analyzer series like NWT4000, D6 JTGP-1033, Simple Spectrum Analyzer, and so on.
Video trigger, real-time trigger, and fast-cycle feature
ADALM-PLUTO custom gain table and Extended linearization table for all devices
Over on YouTube channel "Privacy & Tech Tips" has uploaded a video demonstrating how it's possible to run GQRX with an RTL-SDR on a PinePhone. In the video the presenter shows how to set up the screen so that GQRX is fully visible, demonstrates GQRX running, and then goes on to show exactly how to install the RTL-SDR drivers on the PinePhone.
The PinePhone is an open source smart phone that can run a full Linux distribution. A PinePhone sells for US$149.99 or $199.99 for a higher end version with more RAM and storage.
RTL-SDR On The Pinephone! Demo, Installation/Hardware
Of course the image is only grayscale (or in Dmitrii's case he decided to use greenscale), but adding false color and various other image enhancements found in advanced software like WXtoIMG are just standard image processing techniques.
Dmitrii concludes with the following:
Interesting to mention, that there are not so many operational radio communication systems in the world, the signal of which can be decoded using 20 lines of code. The NOAA satellites are about 20 years old, and when they finally will retire, the new ones will most likely be digital and format will be much more complex (the new Russian Meteor-M2 satellite is already transmitting digital data at 137 MHz). So those who want to try something simple to decode can be advised to hurry up.