Mesh and tactical radios are rugged two-way radios that pass messages on for each other, so that a group of them forms its own network with no mobile tower. Armies, police, disaster response teams and drone operators use them. Tactical means made for field operations, where equipment must survive dust, rain and rough handling.
A normal mobile phone sends every call to a tower. With no tower in range, it has no network. A mesh radio connects directly to the other radios near it, and each radio also relays messages for the others. So a message can hop from radio to radio until it reaches the person it is meant for. This arrangement is called a mesh network. If one link is blocked, for instance by a hill, the radios find another path through a different radio. Nobody has to set up the routes by hand.
Modern mesh radios carry much more than voice. They carry live video, maps and the position of every team member. Many are software-defined radios: much of how they work is set by software, so they can change frequency or adjust to interference after a software update. Many use several antennas at once, which helps the signal get through where a single antenna would fail. Messages are encrypted, so an enemy who receives the signal cannot read it.
Consider an army patrol of eight soldiers in the hills of Arunachal Pradesh. There is no mobile signal, and the valley walls block a direct line to the base, 12 km away. Each soldier carries a radio, and one more radio sits on a ridge above the valley. A small drone flies overhead with another radio. The patrol leader films a broken bridge. The video travels from her radio to the soldier at the back, then to the ridge radio, then to the drone and on to the base. When the patrol moves behind a spur of the hill and loses the ridge radio, the network finds a path through the drone alone. The base still sees the video.
Mesh radios also link many drones flying together, in drone swarms, and connect them to the drone ground control station. Demand has grown fast with the use of drones in war.
Mesh radios are not the cheapest choice for every job. Sensors that send only small readings over long distances use a simpler, low-power network such as LoRaWAN.