This sounds like it would be a great fit for https://soprani.ca/ , particularly the long-range communication part of the project: https://wiki.soprani.ca/ThePlan#Long-range_radios . If they were suitable for use in most countries, the 433 MHz bands could be a great way to deliver text and even picture messages in the absence of a cellular network.
Does anyone know off-hand if these bands are generally license-exempt in Canada or the US? It seems that’s probably not the case in the US, per https://en.wikipedia.org/wiki/LPD433 , but I had difficulty finding info for Canada.
I think you could use 900mhz for the same purpose?
Yes, after some more research it sounds like we could probably get similar range with 900 MHz. I had assumed that range decreased significantly with higher frequencies (using 150 MHz (MURS) as the benchmark, where I’ve seen 35+ km range in my testing), but I’m not a radio engineer, and my brief search suggested you could indeed get 40km line-of-sight with 900 MHz, too. 900 MHz also tends to have fewer regulatory restrictions than 150 MHz, which would be good for the project, where we may wish to do mesh and similar things not allowed on 150 MHz.