This project is an experiment to see whether we can use multilateration to identify the location of RF signals using a network of Raspberry Pis with RTL-SDR dongles. The project was inspired by the work of Stefan Scholl - DC9ST and presented by him at the Software Defined Radio Forum 2017 at Frederickshafen.

Our local 70cms repeater, GB3OV, is located in Graveley, Cambridgeshire. In the UK, the 70cms band is shared and the Radio Amateur Service is only a secondary user. Thus we need to be prepared for co-channel interference - and we do experience this. The main source of intereference is low-power locator beacons that are used by cranes to locate their jibs. Locating these devices and then negotiating with the operator to - hopefully - change the frequency can be quite time-consuming. Hence this project to "automate" the positioning task.

Any additional use might be to locate deliberate interference by other licensed amateurs; however this is more difficult because they often transmit over an existing transmission.

The general idea is to produce a small number (probably 3-4) of self-contained units that can be installed at known locations around the repeater. These units will use the techniques described in Stefan's paper to capture and send an IQ data stream to a Master Station running the analysis software. The results of the analysis will be displayed on a website.

The Master Station will probably be a Linux VM running on a publicaly accessible host somewhere.

Installed on the Master Station will be the Analysis Software.

The minion comprises a Raspberry Pi 3B microcomputer with a cheap plugin RTL-SDR Dongle and simple antenna. The total cost should be under £50.00

The Pi will be running [Balena OS][BalenaOS] and a Balena IOT project built from the OV_MLAT_TOOL Github repository. This comprises a number of Docker containers running on Balena OS and controlled from a single point.

The following containers run on the Minion.

This is a pre-defined Balena container that detects if the Pi is connected to a local network. If not, then it presents a wifi hotspot that can be used to configure the Pi's wireless networking settings.

Typically, this is done just the once when the Pi is installed at a new location. If the Pi is connected to the local network using an Ethernet cable, this container is redundant.

This container implements a customised version of the Resilio Sync Peer-2-Peer file transfer node that is used to synchronise the locally captured IQ data stream with the Master Station.

This container implements the custom multilateration code.

Currently, the system requires a master station to connect to. A future modification would be to move the Master into something like Amazon Web Services