Most countries, even the harshest dictatorships have some form of Land Mobile Radio dealers and a licensing scheme. Non line of sight communications in mountainous areas are usually High HF to Low VHF, 25 to 75 Mhz. They often involve a repeater opposite the mountain face, typically on another mountain. A license, either business band or amateur radio for non-profit events, is required. Unless this is some sort of strange hobby project, the original poster would be wise to use Cellular or contact a Professional.
I can attest from years of doing this that line of sight is a "relative" thing. If you truly do not have a direct shot, or there is a forest, jungle, or dense foliage on the mountain, you end up needing a repeater, or specialized techniques like "Near Vertical Incident Skywave" or Packet Radio. Often your comms may have multipath or diffraction issues as well.
Rarely will license free anything work well at your specified distance without large fixed antennas, or dishes/panel antennas in the case of microwave. 2.4 Ghz WIFI exists because that frequency is strongly adsorbed by anything organic, like trees and even water vapor in the air. Other then for Radar and point to point links, the 2.4 Ghz band is pretty much useless otherwise. Which is why WIFI is stuck there, the high adsorption makes it impractical to sell the frequency to cellular companies.
This is not a "chipset" problem, this will require a moderate to high power radio, most likely a minimum of 5 or more watts at VHF, and most likely a type approved radio, certified by your local agency that handles RF regulation. Or a microwave system with a modest ERP if you have true line of sight.
You will need really good antennas, and a good antenna usually means that you will be violating the allowable "Effective Radiated Power" for a license free service.
Often the frequencies used are shared and coordinated, and while your nearest co-user may be 50 Kilometers away, you will not have "private or secure" in most cases. In my country, the simplest Business/Personal license for a coordinated frequency is 90 Dollars for five years plus a small fee to a private non-profit company that allocates the channels. That gets me five channels 6.25 KHz wide, of which I can use one at a time. There are five more channels paired with my channels five Megahertz up. These are the repeater outlet channels, if I need a repeater. I'm supposed to limit my activities to a 50 mile radius of the license point. I cant send data over a repeater with the present license.
There are un-allocated "free" channels, but everybody and their brother/sister uses them, so I prefer sharing with 10 users across the region rather then anyone who can buy a radio at Amazon or Walmart.
By the way, use my allocated frequency without an ID, and its a happy day on Sheldor while I ENJOY hunting you with a spectrum analyzer and various other techniques. Not much will happen when I find you, other then a simple request to cease and desist. If you don't, I document your signal with a screen shot and report it to the authorities. I'll give you an example:
Last time such an event happened, I as a local ham, moderated the relations between a home owner and a local two way radio company. She was threatened with a 8,000$ a day fine, and could not understand that an oscillating TV antenna preamp was taking out a repeater input. She refused access to her home, and the radio company had already called the FCC. After all, she did not own any transmitters as far as she was concerned.
She started calling around, including the local electronics store, trying to find a way to "Keep these strange men" out of her house. The broken preamp oscillated on the input of a digital repeater leased to Federal law enforcement. I just so happened to be at the parts store. I called her, then I called the company and explained her situation, they explained about tracing the signal to her attic. I called her back, , told her basically a warrant would not even be required, and urged the president of the company to reign in his overzealous technicians. I told him to buy her another pre-amp, pop up at the house door with it in a suit and with business card, and all would be over. That worked. Moral of the story, use a frequency where your allowed to be. The next day a Federal Marshal and the FCC Engineer would have been at her place, and neither would not have been a happy fellow.
I'm also aware of a Swiss case where a Ham repeated a urgent distress call, saved a life, and lost his license and government job in the process. Listening to an un-authorized frequency with a scanner...
In most nations, the license free frequencies are bordered by licensed allocations, and if you stray.. you do so at your own risk. If you do not know and check you can end up disrupting "Safety of Life" communications. Possession of the device after a complaint is pretty much an open and shut case.
If you really need this, consult a professional, or get a amateur license for all involved if you are doing a non-commercial project. Most Nations now just have a "multiple choice" test to get the license and a modest fee.
Steve
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