An excellent question, but very difficult to answer. It depends on the following (in order of importance):
- The height of the antennas above the average terrain.
- The terrain itself – vegetation and buildings.
- The over-the-air data rate. For example, 4800 baud works much further than 9600 baud.
There are only two good methods to determine range. Either create an accurate computer model of the system and the terrain, or drive the area and test the coverage. Since these can be impractical at times, here are some “rules of thumb” for 4800-baud communications range. 9600-baud range is approximately ½ of these.
In flat wide-open areas, such as deserts, grasslands, and farms, vehicle-to-vehicle communications will be 2 miles on the low end and often as much as 10 miles on the high end. A base-station, either with a 15-meter tower or placed on a local hill, will reliably communicate out to 10 miles, and often out to 20-30 miles.
In a rolling hills area, such as much of Nevada, Wisconsin, or Baja Mexico, vehicle-to-vehicle range will be 1-2 miles as long as both vehicles are not in a valley. The range will often go up to 15+ miles as both vehicles crest hills. A base-station, either with a 15-meter tower or placed on a local hill, will reliably communicate out to 7 miles, and often out to 20-40 miles.
In mountainous areas or wooded hills, such as much of Colorado, Tennessee, and northern California, vehicle-to-vehicle range will be ½ – 5 miles and will also be very sporadic depending on the terrain between the vehicles. The M7 GX takes advantage of this by frequently reporting its position, so that as vehicles crest peaks, they can receive location transmissions from a long way away. Often the vehicle-to-vehicle range will be as far as 15+ miles as the vehicles both crest hills. A base-station placed on a mountain top can extend reliable communicate out to 10+ miles, and often out to as much as 50 miles.
In urban areas and cities, structures will create multi-path and interference, reducing the usable range. Communications will be very similar to operation in rolling hills. Vehicle-to-vehicle range will be 1-3 miles. A base-station either with a 15-meter tower or placed on a local hill, will reliably communicate out to 5-7 miles, and often out to 10 miles.