Building a Local Mesh Network

LoRa (long range) is a radio modulation that trades speed for distance: it moves tiny amounts of data, but it can do so over several kilometres with milliwatts of power, in licence-free bands. Two open-source projects turn inexpensive LoRa boards into a self-healing text mesh that your phone talks to over Bluetooth: Meshtastic and MeshCore. This guide gets a small group up and running. For the architecture behind them, read Meshtastic, MeshCore and Off-Grid and Mesh Networks.

1. Choose the firmware

The two do not interoperate. Pick one for your group and area; check which one people near you already run.

2. Get hardware

Common boards include Heltec LoRa 32 and Wireless Stick boards, LILYGO T-Beam (with GPS) and T-Echo, and RAKwireless WisBlock kits. Both projects publish lists of supported devices. You need:

• the right frequency for your region: 868 MHz in Europe, 915 MHz in the Americas and Australia, others elsewhere. Using the wrong band is illegal and works badly;
• a decent antenna (the stock antennas on many boards are poor; a tuned antenna is the cheapest upgrade);
• a battery (most boards take a single 18650 or LiPo cell), or a small solar panel for a fixed node.

Never power on a LoRa board without its antenna connected; that can damage the radio.

3. Flash the firmware

• Meshtastic: the web flasher at https://flasher.meshtastic.org/ from a Chromium-based browser over USB.
• MeshCore: the web flasher linked from https://meshcore.co.uk/ or the project's GitHub.

Then install the phone app, pair with the radio over Bluetooth, and set your region before anything else.

4. Make it private

• The default Meshtastic channel is not private. Its key is publicly known, so anyone running Meshtastic nearby can read it. Create your own channel with a randomly generated key and share it with your group by QR code, in person.
• Direct messages between Meshtastic nodes are encrypted with public-key cryptography (since firmware 2.5), so only the recipient can read them, but relaying nodes still see who is messaging whom.
• Position sharing leaks your location. Turn it off, or reduce its precision, for anyone who should not be found.
• Node names are broadcast. Do not use real names.
• Radio can be located. A transmitting radio can be found with direction-finding equipment. This is a real risk under a hostile government; transmit only what you need.

5. Placement is everything

LoRa needs line of sight more than power. A node on a rooftop, hilltop or high window reaches far further than ten nodes at street level. Plan a few fixed relay nodes in high places (Meshtastic's router or repeater roles; MeshCore's dedicated repeater firmware), powered by solar panels where mains is not available, and keep handheld nodes as clients.

6. Respect the rules

In licence-free bands there are limits on power and, in Europe, on duty cycle (the share of time a device may transmit, for example 1% or 10% depending on the sub-band). The firmware enforces sensible defaults when the region is set correctly. If you are a licensed radio amateur and enable ham mode to use more power, encryption is switched off, because encryption is not permitted on amateur bands.

7. Practise

Run a drill: everyone switches phones to airplane mode with Bluetooth on, and the group coordinates a meeting point using only the mesh. You will find the dead spots, the confusing settings and the flat batteries before they matter.

Going further

• Reticulum is a full networking stack that can run over LoRa, packet radio, Wi-Fi and the internet at once, with end-to-end encryption and its own addressing.
• Briar and Bitchat mesh phones directly over Bluetooth with no extra hardware.
• Naming on Mesh and Off-Grid Networks covers how services are found without DNS.

Sources

• Meshtastic documentation, Introduction, Supported hardware and Encryption: https://meshtastic.org/docs/introduction/, https://meshtastic.org/docs/overview/encryption/
• Meshtastic, Firmware 2.5 release notes (public-key encrypted direct messages): https://github.com/meshtastic/firmware/releases
• MeshCore project: https://github.com/meshcore-dev/MeshCore
• ETSI EN 300 220 (short range devices, 25 MHz to 1 GHz), duty-cycle limits in Europe: https://www.etsi.org/
• Reticulum Network Stack manual: https://reticulum.network/manual/

Continue with APRS and Build a community Wi-Fi network.

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