Transferring Files via the BlockStream Satellite with Lightning Network Payments and RTL-SDR + Transacting Bitcoin over HF

The Blockstream satellite API is now live on the main Bitcoin network. Blockstream satellite is a project that aims to use geosynchronous satellites to strengthen the Bitcoin network by continuously broadcasting the Bitcoin blockchain all over the world. This allows people without internet access (or with censored internet) to receive Bitcoin. Setting up a Blockstream satellite receive station is a matter of building an RTL-SDR based receiver (or other GNU Radio compatible SDR) with a small satellite dish and LNB.

The API was also updated and this has enabled a feature that allows you to upload a file of up to 10 kB via the internet, which will then be transmitted via the satellites to anyone who is running a Blockstream RTL-SDR satellite receiver. Payment for the transmission is taken via the Bitcoin Lightning Network and transmissions appear to work on a priority basis, with larger payments receiving higher priority. The file is distributed to all receivers, so they note that private messages would need to be encrypted with public keys distributed to recipients in other ways. This service is similar to what the Othernet (prev. Outernet) network offered in the past with the ability to transmit data, tweets and APRS messages over their satellite network. We think that cheap small data satellite transmissions could have some interesting applications in remote control.

In related news on CryptoNewsZ it has been reported that a bitcoin lightning network transaction was completed over the 20M amateur radio band. The transaction was completed with the JS8 digital mode, which is similar to FT8 but designed for weak signal usage. The message was sent via the help of twitter, with @eiaine first sending money to @nvk via the internet. @nvk then sent the Lightning Network invoice over 21 JS8 messages via the 20M band to @eiaine who received it, thus confirming that the transaction was completed.

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Demonstration of Two SatNOGS Rotators

Thank you to IZ5RZR for writing in and sharing his two SatNOGS rotator builds with us. SatNOGS is an open source project that aims to make it easy for volunteers to build and run RTL-SDR or other SDR based RF ground stations that automatically monitor satellites, and upload that data to the internet for public access.

IZ5RZR writes that he's now made two rotators and one was modified to use a 5:18 stepper motor (which is upgradable to 50:1) to give more torque so that heavier antennas can be turned smoothly. His rotators are powered by a 12V battery charged by solar, and they can be controlled over WiFi with a PC/tablet/phone. He's also tested the rotators with a 24 dB parabolic grid antenna and found that the rotator could handle it even without a counterweight. He also notes that together with IK5XWA they've fixed a "Meridian Flip" bug in the firmware.

The video below shows the two rotators in action.

IZ5RZR Two SatNOGS Satellite Rotators

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DIY Software Defined Ham Transceiver With eBay Parts

YouTuber jmhrvy1947, has recently uploaded a number of videos giving an overview of how he built his own HF SDR transceiver using what he calls the “Lego build method”. The idea of the Lego build method was to build a transceiver with parts picked and pulled from eBay so that it could be easily reproduced by others. There are a few scratch made components however those designs are available on his GitHub page. The SDR only functions within about 100 kHz of spectrum at a time however for amateur radio HF work this is more than sufficient. Bare bones the radio puts out a mere 100 mW and although the output power is small, he’s made contacts up to 450 miles away using CW (Morse code). You also have the option of adding an amplifier on  your output if you are looking for more power than that. His final revision currently puts out 100 Watts.

Using modified versions of fldigi and Quisk he is able to easily work various digital modes and sync the transmitter and receiver together. The only real down side to this radio is that you must switch out your receive and transmit filters whenever you wish to operate on different bands, a process that really only takes a moment or two.

Check out his videos on the project – it’s really amazing to see what can be done with a small budget these days in radio and with how far software defined concepts have brought us.

DIY SDR CW Xcvr Project

In the video below you’ll see an explanation of the software involved in this build.

DIY SDR CW Software

 

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A Worldwide Map for HRPT Weather Satellite Receive Stations

Recently Manuel (DO5TY aka Tysonpower from YouTube) wrote in and wanted to share his website that shows HRPT weather satellite receive stations from around the world on a map, and links to their Twitter pages where you can see the latest images that have been uploaded. The database also describes the SDR and antenna equipment used by each station. Currently there are 10 stations on the map, and Manuel encourages other people to submit their stations to the map database too. If you are interested in contributing your station to the map, please see Manuel's blog post for more information.

Since the satellite broadcasts a live image of what is currently being seen by the weather camera, each receiver location receives a live view of their part of the earth only. The end goal of Manuel's HRPT station map is to crowd source and collect multiple images of different parts of the earth to create a large HRPT composite image. In a previous post, Manuel who is based in Germany was able to create a beautiful composite image covering Germany, the Atlantic Ocean and Canada with the help of a station in Canada. With more contributors larger and more complete composite images of the Earth could be created.

HRPT is a high resolution weather satellite image signal that is broadcast from the same NOAA satellites that provide the more commonly received low resolution APT images at 137 MHz. HRPT is also broadcast from the Feng Yun and Metop-A satellites. However, HRPT transmits at 1.7 GHz, so a high gain dish antenna with motorized tracking mount, LNA and high bandwidth SDR like an Airspy is required to receive it.

HRPT Station Map
HRPT Station Map
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New Technical Textbook on SDR and Communications: “Wireless Communications From the Ground Up – An SDR Perspective”

Thanks to author Qasim Chaudhari for writing in and sharing with us that his new book titled "Wireless Communications From the Ground Up - An SDR Perspective" has been released. Qasim is a research fellow in the Electronic and Telecommunications Engineering department at RMIT University in Australia and has been giving presentations and talks each month at Cyberspectrum Melbourne for more than 3 years.

His book covers University level wireless communications and digital signal processing (DSP) topics with a focus on SDR. Qasim writes that most DSP books that he's seen in the past were written for professional academics which made them difficult to for other technical (but non-mathematical) persons to understand. You can't explain DSP without equations, but Qasim notes that his book aims to keep the math content at school level only, and with plenty of figures to help with visualization. The description reads:

There are different angles from which this book contributes to the understanding of wireless communication systems from the perspective of a Software Defined Radio (SDR).

  1. In my opinion, any language, including that of mathematics, is an unnatural mode of communication. For example, I can write the words darwaza, porte, puerta, umnyango, ovi and only certain people will understand what I mean. However, if I show you an image of a door, almost every single person on the planet will immediately get the concept. A figure imprints a massive amount of parallel information in our brains that is much easier to process and recall later. Since a human mind handles images very well, I try to visualize equations through beautiful figures which you will encounter throughout the text with logical and intuitive explanations.
     
  2. If you are not a pure wireless communications academic, you would have found that the mainstream textbooks on this topic are filled with heavy mathematical details which makes this field an exclusive membership club for those who can understand several types of frequency variables and their corresponding Fourier transforms, probability and random processes and detection and estimation theories. While this is true for becoming a master, the Software Defined Radio (SDR) revolution and subsequent projects like GNU Radio have made it possible for anyone to sit down and construct their own unique radio by writing code. Many even do not need to know most of the above mentioned topics. All they need to understand is why an algorithm does what it does so that they know how to write its code, or modify it in an even better way. For this purpose, I have only relied on school level mathematics to explain all the concepts. You will not find any e or j of complex numbers here, nor will you encounter any integrals, probability theory and detection or estimation theory. The only things to know are a sine, cosine and a summation as well as a derivative (which I have occasionally used).
     
  3. The best books written on implementing digital communication systems using Digital Signal Processing (DSP) algorithms are by fred harris (Multirate signal processing for communication systems) and Michael Rice (Digital communications – A discrete-time approach). As often happens with the grandmasters, they walk on a trail without exactly clarifying it for others. After reading their books, I started to feel that fred harris has mainly focused on `how' of communication systems in an unprecedented detail while Michael Rice has mainly covered `what' of communication systems in his simple and beautiful style. In this process, there were many `why' generated in my mind for which I had to find satisfactory answers. This book is a collection of those simple answers.
     
  4. An extra little bonus is a one page summary of the crux of Rx algorithms, clarifying the role of particular parameters in the signal waveform. Most of the algorithm design can be understood by just grasping the concepts on this one page.

A common theme in this text is that some concepts seem easier in time domain and some others are simpler in frequency domain, while their mathematical derivations reinforce the idea. It is fun to grasp a concept covering all three sides. Finally, the book contains a few examples from GNU Radio that explain how to set the parameters in some blocks (e.g., Costas loop, band edge FLL, polyphase clock sync, etc.).

The book is currently available on Amazon, and on Amazon you can see a preview of some pages from the book. Qasim also has a website for the book here.

Wireless Communications from the Ground Up: An SDR Perspective by Qasim Chaudhari
Wireless Communications from the Ground Up: An SDR Perspective by Qasim Chaudhari
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SignalsEverywhere Video: SDRAngel How to Receive Basics Tutorial

Over on his YouTube channel SignalsEverywhere, Corrosive has posted a new video tutorial explaining how to use the SDRAngel software for receiving signals in Windows. SDRAngel is a general purpose SDR program similar to programs like SDR#, HDSDR and SDR-Console, however it's layout and workflow is slightly different compared to other programs. SDRAngel also has some interesting features such as built in decoders for DMR, D-Star and Fusion digital voice signals and unlike most other general purpose SDR programs, SDRAngel is also capable of controlling transmit capable SDRs. Corrosive notes that he will discuss that feature in a future tutorial.

Corrosive's tutorial goes over the main points such as changing gain, changing sample rate, tuning to signals, and adding demodulators. In the video he uses an RTL-SDR as the receiver.

RTL SDR SDRAngel Tutorial - How to Receive Basics and More

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Photos of the MSi.SDR Dongle: A New SDRplay RSP1 Clone

Thank you to reader Mikael for writing in and letting us know that over on Aliexpress a new clone of the SDRplay RSP1 has been starting to show up. The sellers are terming it as the "MSi.SDR" in reference to that fact that it uses the Mirics MSi chips, which are the same chips used in all SDRplay SDRs. Currently the MSi.SDR is selling for about US$65 on Aliexpress.

In the past we've seen other SDRplay clones but this is the first version in a dongle format, and the first time that it is actually priced cheaper than the original. SDRplay and Mirics are owned by the same people, and Mirics note that they have not distributed any chips in over 5 years, so it a mystery as to why there are suddenly a lot of unauthorized Mirics chips available on the Chinese market. It is unclear if SDRplay will be able to enforce their IP rights in China, but it seems unlikely.

Mikael has provided some good photos of the PCB from the version he received which we show below. It appears to be similar to the RSP1, so it is missing the new features and filtering improvements of the newer RSP1A. When connected to a PC it shows up as an RSP1, so all compatible SDRplay software including SDRuno and HDSDR with the official SDRplay EXTIO should function with it.

Mikael writes:

I have seen this sdr on various China sites for quite some time and lately on ebay as well, I was kind of sure it was a rsp1 in a new pcb layout as it claimed it to be 10khz to 2Ghz with a 10Mhz bw and 12 bit resolution and containing an msi chipset with a 0,5ppm tcxo.

I ordered one two weeks ago from aliexpress for about 67$ incl postage and got it in the mail today, it was delivered with a micro usb cable and a magnetic telescope antenna with an about 2m coax cord.

pluged it in and watched the device manager, as I have a rsp1a and a rsp2 I already had the drivers loaded for those, and sure, it was identified as an rsp1, so I did a quick test and and started hdsdr and and selected the extio.dll for the rsp1, it started up as it should and it behaves just as a rsp1, did a quick tunearound in the 3,5 and 7Mhz band and it was working well, have not done any in depth analys yest, will examine the pcb to see if there is any kind of filtering in there.

In an upcoming post we plan to compare the various SDRplay and Airspy clones available on the market with the originals.

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Testing an SDRplay RSPduo with Bonito Active Loop Antennas

Bonito is a company that sells various active dipole and loop antennas for ham radio and DX applications. Recently they decided to test their MegaLoop FX and MegaDipol MD3000DX antennas on an SDRplay RSPduo, and compare it against a higher end WinRadio. Bonito found that the RSPduo performed well on the weaker longwave stations, but the Winradio outperformed it on the stronger ones. The differences were due to the better dynamic range of the Winradio.

The article goes on to make some recommendations for using their antennas on the RSPduo. They write that if intermodulation due to very strong signals occurs, there are some fixes that can be applied on their antennas to desensitize them and prevent overload. With the loop, a smaller loop size should be used, and the gain selector should be set to medium or min. With the dipole, they note that shortening the elements, and using it in an L-configuration with the lower radiator pointing towards the interfering signals can be used to attenuate them out. This works because a dipole configured in a L shape provides a bit of directionality.

The article also notes how grounding, very good coax shielding, good quality USB cables and galvanic isolation are all very important for reducing noise.

Bonito RSPduo Antenna Test Setup
Bonito RSPduo Antenna Test Setup
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