Use this tool to calculate how far a VHF radio can transmit.
Enter the antenna height and pick the units (meters or feet).
d = 4.12 * √h
where h is the antenna height in metres and d is the distance in kilometres.
For a height of 12 feet, the range of a VHF radio system is 5 miles or 8 km. Note that this assumes no obstructions.
VHF (very high frequency) is the name for radio frequencies in the range between 30 MHz and 300 MHz. VHF signals are used for FM Radio, Two-way radio, television broadcasting, AIS and other applications.
 Line of Sight Propagation on Wikipedia