Leaderboard

The range of a UHF radio will be pretty much limited to line of sight. If your antenna is 6 feet off the ground, its distance to the horizon is 3 miles. If the antenna for the other radio is also at about 6 feet, then you have an approximate theoretical range of 6 miles. Trees, structures, land, antenna gain, RF interference, output power, etc will all have an effect on this range. If you're currently getting 3 miles simplex between radios, that's pretty good! You are also correct in that your current antenna placement on the Jeep spare tire is less than ideal. The best location for a mobile antenna is always the center of the roof - this is the highest point on the vehicle and the surface area of the roof will provide a ground plane. Is this is the antenna you are currently using? I * think * this is a 5/8 wave antenna, which will require a ground plane to operate efficiently. Since you're in a jeep, a fiberglass roof is not a great surface for that ground plane (and you may not even have a roof at times..) so you should look into 1/2 wave antennas, which do not require a ground plane to operate. The antenna should still ideally be mounted as high on the vehicle as possible.