I have recently found something that I think would be very helpful for people who want to do long-range wireless projects such as weather balloon trackers.
Of all of the long-range high power transmitters that I have seen used for the arduino, the most popular seems to be the XTend 900. It is a 1 watt 900 MHz transceiver that you don't have to get a Ham licence for and it has over a 40-mile range in optimal conditions. The only problem is the hefty price tag of over $200 dollars. This is only the cost of one and for most cases, you would need two.
I have come up with a couple of alternatives for high power wireless communication, particularly for weather balloons.
A couple of months ago I came up with the idea of using a cheap 100 mW 433 MHz wireless module, such as the HC-12, with an RF amplifier. On eBay, for $20 you can buy a 2 watt RF amplifier which you could hook up to the wireless module to increase the output power. Although this stops the module from being able to receive, a second module could be used to receive. With this setup, you could get twice the output power for less than $50.
Recently I found this website called Alibaba which is an Amazon-like seller where you buy everything directly from the producers. Although it is mostly in bulk, some items can be bought in smaller amounts.
After searching around, I found that they have a large assortment of uart wireless modules. Although most of them are low power, I found a 2-watt uart transceiver for $50. They have a receive sensitivity of -121 dbm which is 5 more dbm then the XTend module.
Although 2 watts is above the legal limit for unlicensed use, it is possible to lower the output power of the transmitter through uart commands.
Also, it comes with antennas and usb converters if you want to hook it up to a computer.
The link for the transceiver is here
I wanted to share this information although I haven't tested it yet.