SFWEM.NET is the San Francisco Wireless Emergency Net, which is a mesh network that’s being built out by amateur radio operators with the intention of being a communications backup in time of emergency — when phone and data networks may be locally overwhelmed or not functional. Beside that, however, it’s an interesting experiment for amateur radio operators seeking to understand the benefits and limitations of “wi-fi” as a long-distance tool.The wi-fi that most people know is range-limited and often flakey. SFWEM works with directional antennas that have far greater range, and with higher radio power (permitted to amateur radio operators) on a band of radio frequencies not available for public use. So rather than being stuck with a 50-foot maximum range, we can get good connections over distances of 20+ miles. The connections are still line-of-sight, meaning that one antenna must be able to literally “see” the antenna on the other end that it’s connecting to. Any buildings, trees or hills in between the two will reduce or eliminate the signals.
So the idea is to create a mesh or network of interconnected stations to cover the space — in this case the northern end of San Francisco Bay, and soon the southern end of Marin County — with stations that automatically relay communications from one node of the mesh to the next. And as long as even one mesh node has a connection to the Internet, all of the other interconnected mesh nodes can reach the Internet (and each other).
My “interconnection” consists of the packet radio station, which is linked to the amateur packet radio network in the area (in my case to KE6JJJ in Bernal Heights, and to NøARY in the South Bay). And two nodes on the SFWEM mesh. The link between the two is software. A JNOS software system running on a Raspberry Pi4 computer. JNOS can send and receive messages on the packet side, and can send, forward and receive messages using regular Internet-based email.
The whole setup is currently solar powered. Summer in San Francisco is cold, and sometimes foggy, but there are enough sunny days that the batteries can make it. (Winter, with different sun angles, is a bit more challenging.) Currently (May 2021) I’m testing to determine how long the solar powered system can supply both the packet and the SFWEM systems, as well as solving some issues with how many different voltages are required for all of this equipment, and how efficient the whole power supply thing can be.
Lots more to say; enough for now.