Recently we came across Electrosense which is an interesting open source project that aims to deploy radio spectrum sensors worldwide in order to analyze and understand radio spectrum usage. This information could be extremely valuable in order to make more efficient use of the limited radio spectrum, and for detecting sources of interference and illegal transmissions. The hardware that Electrosense uses consists of just an RTL-SDR, Raspberry Pi, antenna and an optional GPS for time synchronization.
The ElectroSense network is a crowd-sourcing initiative to collect and analyse spectrum data. It uses small radio sensors based on cheap commodity hardware and offers aggregated spectrum information over an open API.
The initiative's goal is to sense the entire spectrum in populated regions of the world and to make the data available in real-time for different kinds of stakeholders which require a deeper knowledge of the actual spectrum usage.
ElectroSense is an open initiative in which everyone can contribute with spectrum measurements and access the collected data.
There are already several spectrum sensing projects in the works by big companies like Google, Microsoft, and IBM, but these only cover a small portion of the spectrum, or use high cost sensing stations limiting their ability to be deployed on a wide scale. Electrosense solves these problems by using low cost RTL-SDRs, and a crowd sourcing paradigm.
At the time of writing there are 103 sensors registered to the Electrosense network, with 23 being online, most of which are in Europe. Once you register an account on their site, you can browse the active sensors. Clicking on the spectrum button for a sensor brings up a live spectrum graph. For example in the screenshot below we access the data from an RTL-SDR + downconverter sensor in Madrid. We're able to see a live wideband 20 MHz to 6 GHz spectrum scan, and graphs of frequency occupancy rates.
In addition to the standard SDR hardware being used, they've also designed a very interesting open hardware/source DC to 6 GHz up/downconverter board. The board is USB controlled, and switches between the upconverter for the lower HF bands, pass through for receiving DC- 1.6 GHz, and the downconverter for receiving up to 6 GHz. It has a 20 MHz output bandwidth which means that wide band SDRs can also make use of it.
The Electrosense website notes that anyone can host a sensor, and if you meet their criteria (permanent internet connection, ethernet connectivity and a low interference location) you can apply for a free kit. If you aren't selected for a free kit, then the Jetvision store based in Europe is selling Electrosense kits that include an RTL-SDR Blog V3, Raspberry Pi 3, power supply, SD card with preinstalled Electrosense software, and either our multipurpose dipole antenna, or a wideband discone with 15m of low loss cable for roof mounting.
The Electrosense team have been working hard on this project and have already published several related papers and a magazine article about the Electrosense network and it's use cases. One interesting paper discusses a method for decoding wideband signals using a network of non-coherent RTL-SDRs. Another paper discusses using using deep learning for automatic signal classification. The full list of publications can be found on their publications page.
If you're interested in this type of crowd sourced spectrum project, then you might also want to take a look at the KiwiSDR which is a networked 0 - 30 MHz SDR. Multiple crowd sourced KiwiSDR's can be used in a TDoA calculation for determining transmitter locations.