My goal is to build a battery powered RF transmitter that will reach its accompanied receiver through trees, tall grass, brush, and some outside terrain at a reasonable distance (up to a couple miles would be great).
The main thing I want to focus on is the transmitter for now but for completeness, think of the receiver as a handheld device. The transmitter needs to be small and run on a small battery. The antenna can be probably a foot long. Basically think of those GPS dog collars that emit their GPS location via RF, as this is essentially what I'm hoping to make.
I am expecting that I will want/need to use a transmitter in the 900MHz range as that seems to be what would work best for this application based on what my research has shown. Unfortunately I'm having a difficult time figuring out what a good chip or module would be to use in this case. I will likely need to pair it with a GPS chip and a simple microcontroller(?).
I expect the data rate needs for this will be as follows:
- 6 bytes for a fairly precise GPS coordinates
- Between 4 and 32 bytes for a unique identifier
- Some packet overhead
- I think transmitting this message once per minute would be plenty sufficient and it would still be usable at higher periods (5 minutes?)
I'm not sure what the packet rate limitations are at the 900MHz range or the max power output (2 Watts maybe)? Are companies like Garmin able to achieve this by via licensing? If I used license hardware would that make a difference?
I have a good amount of software experience and some assembly/C/C++/C# for the programming aspect of the microcontroller but hardly any RF or signal processing experience.
Can anyone recommend some components that would be useful for this application? Explanations for why these components would work best would also be helpful.