Category: Applications

Receiving the Bitcoin Blockchain from Satellites with an RTL-SDR

Bitcoin is the worlds first and most popular digital currency. It is steadily gaining in value and popularity and is already accepted in many online stores as a payment method. In order to use Bitcoin you first need to download a large database file called a ‘blockchain’, which is currently at about 152 GB in size (size data obtained here). The blockchain is essentially a public ledger of every single Bitcoin transaction that has ever been made. The Bitcoin software that you install initially downloads the entire blockchain and then constantly downloads updates to the blockchain, allowing you to see and receive new payments.

Blockstream is a digital currency technology innovator who have recently announced their “Blockstream satellite” service. The purpose of the satellite is to broadcast the Bitcoin blockchain to everyone in the world via satellite RF signals, so that even in areas without an internet connection the blockchain can be received. Also, one problem with Bitcoin is that in the course of a month the software can download over 8.7 GB of new blockchain data, and there is also the initial 152 GB download (although apparently at the moment only new blocks are transmitted). The satellite download service appears to be free, so people with heavily metered or slow connections (e.g. 3G mobile which is the most common internet connection in the third world/rural) can benefit from this service as well.

The service appears to be somewhat similar to the first iteration of the Outernet project in that data is broadcast down to earth from satellites and an R820T RTL-SDR is used to receive it. The blockstream satellite uses signals in the Ku band which is between 11.7 to 12.7 GHz. An LNB is required to bring those frequencies back down into a range receivable by the RTL-SDR, and a dish antenna is required as well. They recommend a dish size of at least 45 cm in diameter. The signal is broadcast from already existing satellites (like Outernet they are renting bandwidth on existing satellites) and already 2/3 of the earth is covered. The software is based on a GNU Radio program, and can be modified to support any SDR that is compatible with GNU Radio. They write that the whole setup should cost less that $100 USD to purchase and set up.

To set it up you just need to mount your satellite antenna and point it towards the satellite broadcasting the signal in your area, connect up your LNB and RTL-SDR and then run the software on your PC that has GNU Radio installed.

More details can be found on the Blockstream Satellite website, and technical details about the software and hardware required can be found on their GitHub page.

How the Blockchain satellite works (From
How the Blockchain satellite works (From

Some may wonder what’s the point if you can’t transmit to the service to make payments with it. Over on this Bitcoin Reddit thread user “ideit” explains why it’s still useful in this nice quote.

You sell goats in a small village. A customer wants to buy a goat, but you have no banks so people have put their money into bitcoin. Your customer goes to the village center which has a few computers hooked up to the internet. He sends you payment then comes to get his goat. You don’t have internet near your goat farm, but you’re connected to the satellite so you can see he sent you payment and you give him his goat.

Or, you live in an area that caps your bandwidth. You want to run a full node, but downloading blocks eats away at your cap. Connecting to a satellite reduces your bandwidth usage.

Or, you’re using an air gapped laptop to sign transactions from your wallet for security reasons. You can now connect that laptop to the satellites so your laptop can generate its own transactions without connecting to the internet.

Or, your internet connection is terrible. You can usually broadcast transactions since they’re small, but downloading blocks and staying in sync with the blockchain is literally impossible. Connect to a satellite and now it’s simple.

Listening to Astronauts on the ISS with an RTL-SDR and V-Dipole (ARISS Contact with Astronaut Paolo Nespoli)

Manuel a.k.a ‘Tysonpower’ has been using his RTL-SDR (and his Baofeng) to listen in on ARISS contacts from the International Space Station (ISS). ARISS stands for Amateur Radio on the ISS, and is a program often used by schools to allow students to contact and ask questions to astronauts on the ISS with a ham radio. It is possible for anyone to listen in on the downlink (astronaut speech) if the ISS is over your location while transmitting. The uplink however may not be able to be heard as the signal is directed upwards towards the station.

For his first try he used a Baofeng (cheap Chinese handheld) and a DIY Carbon Yagi. For the second contact he used his RTL-SDR V3, an FM Trap and an LNA4ALL on a V-Dipole antenna placed on the roof of his car. With this set up he was able to receive the downlink transmissions from 1.6 degrees to 1.3 degrees elevation.

Viewing Lightning RF Bursts with an RTL-SDR

Lightning produces fairly wideband bursts of RF energy, especially down in the VLF to HF frequencies. Detecting these bursts with custom radio hardware is how lightning detection websites such as work.

It is also possible to detect lightning using an RTL-SDR that can tune to to HF and lower, such as the RTL-SDR V3, or an RTL-SDR with an upconverter. Over on his blog Kenn Ranous (KA0SBL) has uploaded a short post showing what lightning bursts look like on an RTL-SDR waterfall. He uses an RTL-SDR V3 to tune down to the LF – MW frequency bands and looks for wideband pulses of noise which indicate lightning.

It would be interesting to see if this type of detection could be automated with DSP so that a similar service to could be created.

Lightning Pulses
Lightning Pulses

Receiving Outernet with a Grid Antenna and LeanDVB

Recently Luigi Freitas wrote in to us and wanted to share his fairly unique Outernet setup which is based on a Grid dish antenna, low cost SPF-5189 LNA, C.H.I.P mini single board computer generic RTL-SDR, and the open source LeanDVB decoder software.

Last month we made a post about LeanDVB, a lightweight DVB-S decoder, which with a few configuration changes can be used to also demodulate the Outernet signal. Luigi places his 2.4 GHz WiFi grid antenna (which still works for the 1.5 GHz Outernet signal) on a tripod and points it towards the Outernet satellite in his area. He connects the antenna up to a SPF-5189 based LNA, which is a 50 – 4000 MHz LNA that is very cheaply found on eBay for about $7 USD. Then a cheap generic no-TCXO $8 RTL-SDR is used together with the LeanDVB software.

In his post Luigi shows how to set up the LeanDVB software for decoding the Outernet signal by piping the output of rtl_sdr into it, and getting all the settings correct. To get the final files he then shows how to pipe the decoded packets in the Skylark decoder, and then the files can be accessed from the regular Outernet web GUI.

The LeanDVB Decoder GUI showing a successful lock
The LeanDVB Decoder GUI showing a successful lock

Listening to July’s Arecibo Observatory Ionospheric Heating Campaign

During July 24-31 the large Arecibo Radio Observatory in Puerto Rico (the big dish antenna that you may be familiar with from the movie ‘Contact’) ran an Ionospheric heating experiment which involves transmitting 600kW of net power up into the Ionosphere. This type of experiment is used for researching plasma turbulence in the ionosphere and upper atmosphere.

“The new Arecibo ionosphere HF heater nominally transmits 600 kW net power and has a unique Cassegrain dual-array antenna design that increases gain of three crossed dipoles for each band, using the signature 1000-foot spherical dish reflector,” explained Chris Fallen, KL3WX, a researcher at the University of Alaska-Fairbanks HAARP facility. He has reported that Arecibo would use 5.125 or 8.175 MHz, depending upon ionospheric conditions, but emphasized that these are estimates and frequencies may be adjusted slightly. On July 25, Arecibo was transmitting on 5.095 MHz.

Over on YouTube Mike L. used his SDRplay RSP1 together with our BCAM HPF to record some transmissions from the observatory.

Receiving SSTV Images from the ISS with a V-Dipole and RTL-SDR

During July 20 – 24, 2017 the ISS (International Space Station) was transmitting SSTV (Slow Scan Television) images down to earth in celebration of the ARISS (Amateur Radio on the ISS) 20th Anniversary. The ISS transmits SSTV images on celebratory occasions several times a year. More information about upcoming ARISS events can be found on their website

Over on YouTube and his blog, user Tysonpower has created a video and writeup of his experiences with receiving the ISS SSTV images using an RTL-SDR, FM Trap filter and a V-Dipole antenna. The V-Dipole antenna is a super simple satellite antenna for NOAA/Meteor/ISS etc satellites that recently became popular due to Adam 9A4QV’s writeup on it.

Despite Laptop and PC troubles, he was able to capture several images. He also notes that he was able to use a Baofeng and Yagi antenna to receive the signal indoors.

Note that Tysonpower’s YouTube video is narrated in German, but there are English subtitles available if you turn on YouTube’s closed captions which should be on by default on this video.

SDRTrunk Setup and Use Tutorial

Over on his blog John Hagensieker has uploaded a tutorial that shows how to set up SDRTrunk with RTL-SDR dongles. SDRTrunk is an application that allows you to follow trunked radio conversations, and decode some digital voice protocols such as P25 Phase 1. It is similar to Unitrunker and DSDPlus combined into one program. It is also Java based so it is cross platform and so can be used on Linux and MacOS systems as well.

John’s tutorial contains many useful screenshots, so it should be great for a beginner. He starts from the beginning, with finding trunking frequencies over on, then goes on to the installation and use on Linux. He also later explains how the Airspy can be used instead of multiple RTL-SDR to cover 10 MHz of bandwidth so that multiple systems can be monitored.

SDRTrunk Running and decoding a P25 Phase 1 System
SDRTrunk Running and decoding a P25 Phase 1 System

Installing and Using SDRTrunk on Linux for Live Trunk Tracking with an RTL-SDR

SDRTrunk is a cross platform Java based piece of software that can be used for following trunked radio conversations. In addition to trunk tracking it also has a built in P25 Phase 1 decoder. Compared to Unitrunker SDRTrunk is an all-in-one package, and currently it supports most trunking system control channels, but unlike Unitrunker it still misses out on some systems EDACS and DMR.

Over on his YouTube channel AVT Marketing has uploaded an excellent 6-part video series that shows how to install SDRTrunk and the Java runtime environment on Ubuntu Linux. The sections covered include, installing Java, setting the Java environment variables, installing other SDRTrunk prerequisites such as Apache Ant and the JMBE audio codec for decoding P25, and finally actually using and setting up SDRTrunk. Like all of AVT’s other videos, this is an excellent tutorial that takes you through the entire process from the very beginning so is useful for beginners as well.

If you’re new to trunking: Trunking systems are typically used with handheld radio systems (e.g. those that police, security guards, workmen etc carry around). The basic idea is that each radio constantly listens to a digital control channel which tells it what frequency to switch to if a call is being made. This allows the frequency spectrum to be shared, instead of designating one fixed frequency per user which would be very inefficient. But this system makes it difficult for scanner radios to listen in to, because the voice frequency could change at any time. Therefore software like Unitrunker and SDRTrunk which can decode the control channel is required. In addition many new systems use digital audio like P25 or DMR which requires digital decoders like SDRTrunk or DSDPlus.