AREDN
| AREDN | |
|---|---|
| Full name | Amateur Radio Emergency Data Network |
| Type | High-speed data mesh network under amateur rules |
| Hardware | Commercial Wi-Fi and outdoor wireless gear reflashed with AREDN firmware |
| Developed by | A volunteer open-source project |
| Frequencies (US) | |
| 13 cm | 2.4 GHz, amateur channels at and below the low end of Wi-Fi |
| 5 cm | 5.8 GHz amateur allocation |
| 9 cm | 3.4 GHz; amateur access being phased out by the FCC |
| 33 cm | 900 MHz, limited hardware |
| Rules | |
| Encryption | Not permitted under Part 97 |
| Users | Licensed amateurs |
AREDN, the Amateur Radio Emergency Data Network, is a project that turns inexpensive commercial wireless networking equipment into a high-speed data network operating under amateur radio rules. Volunteers install free AREDN firmware on outdoor radios originally made for wireless internet service, set them to frequencies in the amateur bands, and mount them on towers, rooftops and hilltops. The nodes find each other automatically and form a mesh, a network in which each node can pass traffic for the others, so the network keeps working if one link fails. AREDN networks carry computer data, not voice over the air in the usual ham sense, and are used mainly by ARES, RACES and other emergency communications groups.
How it works
An AREDN node is a small radio, usually with a built-in directional antenna, running AREDN's firmware in place of the manufacturer's software. Each node carries its owner's call sign in its name, which the firmware uses to identify the station. When powered up, nodes discover neighbors on the same channel and share routing information, so a computer plugged into any node can reach services on any other node in the mesh, even many hops away.
Links between hilltop sites often span tens of miles using dish or panel antennas with high gain, while sector antennas at a central site serve nodes around it. Where radio paths are impossible, separate meshes can be joined by tunnels carried over the internet, and larger regional networks connect through well-placed hub sites. A mesh is separate from the internet: it keeps working when commercial networks fail, which is the whole point for emergency use.
Frequencies
AREDN hardware is built for unlicensed Wi-Fi bands, but AREDN uses channels that fall within US amateur allocations, where Part 97 permits higher power and higher-gain antennas than unlicensed rules allow. Some AREDN channels lie outside the frequencies ordinary Wi-Fi devices use, which helps avoid interference.
- 2.4 GHz (13 cm). The amateur band overlaps the lower Wi-Fi channels. It is crowded with home Wi-Fi in most places, so channels below the Wi-Fi band are preferred where possible.
- 5.8 GHz (5 cm). The most widely used band for AREDN links, with plenty of channels and compact high-gain antennas.
- 3.4 GHz (9 cm). This band has an uncertain future. In 2020 the FCC ordered the amateur secondary allocation from 3.3 to 3.5 GHz to be phased out to make room for commercial wireless services. Amateur transmissions between 3.45 and 3.5 GHz had to stop by April 2022. Amateurs may for now continue to operate on a secondary basis in 3.3 to 3.45 GHz while the FCC decides that spectrum's future, but must not interfere with the new users. Equipment for this band is no longer manufactured, and AREDN advises considering the risk before installing new 3.4 GHz nodes.
- 900 MHz (33 cm). A small amount of older hardware works on the 33-centimeter band, useful for paths through trees, but suitable devices are scarce.
Most microwave amateur allocations are shared, and amateurs are secondary users on much of this spectrum. Check the current band plan and the AREDN channel charts before choosing a frequency.
What runs on a mesh
A mesh network carries the same kinds of services as any computer network. Common uses include VoIP telephones linking emergency operations centers and shelters, live video from cameras at incident sites, keyboard chat, shared maps and documents, and Winlink email servers. Because these services can be set up in advance, a served agency can be given a working network within minutes of a disaster.
Rules and limitations
Everything on an AREDN network is amateur radio communication, so Part 97 applies. Content may not be encrypted to hide its meaning, which rules out standard Wi-Fi security and limits how networks handle private information. Business use is forbidden, and only licensed amateurs may use the network to communicate, except as the rules on third-party traffic allow. Because the radios share bands with many other users, a well-planned AREDN network depends on careful channel planning and clear line-of-sight paths, since signals at these frequencies are easily blocked by hills, buildings and dense foliage.