We're making an open-source $30 GPS/mesh radio, would like advice

This is awesome! It looks like it could do several things for which I wanted to have a device.

Offline GPS tracker with very long run time for hiking. I'd like up to one month run time. On the other hand I only need low time resolution, one waypoint each minute. It also does not need to send the location anywhere, storing it local is fine.

Offline/Online GPS tracker for paragliding. Battery for one day, but also high resolution tracking, about one waypoint per second.

Long range communication extender for my mobile phone that does not require infrastructure like base stations. (For the prepper in me)

Why? Even 200 in a small area, say a ski resort, mountain bike race, or similar seems perfectly reasonable. Sure not 200 people typing as fast as they can, but plenty for the normal chatter I hear over sms. Especially if you keep the messages short and have a latency of a few minutes be acceptable.

Using the family radios (often $30 ish) on hiking trails, parks, amusement parks, etc. I usually hear minimal chatter, just things like "Anyone seen Bob?", "meet at lift #4", "Lunch in 30m?", "Linda stopped to retie her shoes", etc.

Check out js8call if you want to see how to handle 100s of people with very little bandwidth. Sure it's designed for ham radio frequencies and covers 1000s of miles instead of 1000s of feet, but still man portable

A phone, bluetooth sound card, a HF transceiver, and an antenna is all you need. Generally hams are proud when they get better than 1000 miles per watt.

Dunno, I think one of the biggest weakness of various ham related technologies (and yes I have my general) is the assumption that everyone is online all the time. Trying to communicate with a few dozen people is very inefficient with amateur radio in general. It's usually voice, usually assumes everyone is doing nothing but listening, is listening continuously and has perfect reception. God forbid someone is driving, hiking aggressive terrain, or a group of 10 people is online only 60% of the time each.

Most of the cheap ham stuff assumes a perfect repeater already to do the heavy lifting, which is nice when you have it, but very frustrating when you don't.

I do wish that ham or consumer devices supported digital modes, peer to peer, store and forward, push, pull, query, etc. Js8call supports this, so you can do things like ask when someone was last seen, leave messages on 3rd parties, ask 3rd parties to forward, etc. So even if each radio is online part of the time, and parties that want to talk can not directly hear each other things work just fine. It's amazing to even think about, communicating several magnitudes below the noise floor, power levels so low that hams are proud when they get less than 1 watt per 1000 miles!

Imagine standing on the west cost of the USA, shining a 5 watt flashlight at the sky, having it bounce off the sky, to land, and again into the sky, and again to the last to someone 1000s of miles away... and they can decode your signal. Amazing stuff.

I do wonder what the smallest package you could fit a 1 watt bluetooth connected HF radio in to enable any phone to talk js8call.

My solution for this kind of thing is to support a router that connects to the internet. Then on the internet side run a DHT so all the internet routers/gateways can find each other. Each router would keep track of the devices they have seen recently, and publish them to a DHT. Much how running a bittorrent client for a particular torrent publishes that fact to the DHT so anyone on the planet can find peers of that torrent.

So if Bob at a ski resort in Colorado want to message someone in Germany his message would propagate around the mesh until a gateway noticed it was for a client that hasn't ever been seen by that gateway. The gateway/router would do a DHT lookup, and would find a router in Germany had seen that user recently and forward the message there. Next time that router heard (directly or indirectly) that the recipient was online it would forward it (directly or through store and forward) to the user. Sure this process might take minutes, but generally it would still be useful.

Imagine an island like Haiti or Puerto Rico is hit by a storm and only one in 5000 people has a cell signal or sat uplink. Add a mesh and just a few uplinks for the whole island and important communications could get through. Maybe even putting a sat uplink on a car that could drive around and allow messages in/out even just once a day could be quite valuable. This of course needs to be combined with store/forward messages and the other various delay tolerant network features.

Seems much more useful than using HF radios to scan the planet for open Ham email gateways. I was rather amused to hear that to communicate across Puerto Rico they often ended up sending messages through an email gateway they could reach in Italy... just to get messages across the island.

How will you make sure your customers will be in compliance when operating the device? GoTenna used to have a nice photo gallery of people breaking the law, i.e. using their earlier MURS-band mesh devices abroad.