We are often asked "How far will my 100 watt transmitter go?".
This question does not have a simple answer. WHY? Because there are so many factors that will determine how far your transmitter will go that there is no single answer to this question. For example, here is a list of the factors that will determine the range of an FM transmitter:

1. The amount of output power of the transmitter (TPO)
2. The type of coaxial cable used
3. The amount of coaxial cable used (length of cable)
4. The type of antenna used
5. The height of the antenna above average terrain (HAAT)
6. The amount and height of trees in the area around the antenna
7. The amount and height of buildings around the antenna
8. The type of terrain surrounding the antenna site (Flat or Hilly)

So as you can see by the above list there is no one single answer to the question. You could have two different people both using a 100 Watt FM transmitter and one of them will be getting 15 miles while the other person is only getting 1 mile. The reason could be that the one who is getting 15 miles has a 2-Bay PCP2 antenna mounted on a 15 story office building that is located on top of a hill with gradually downward sloping terrain in all directions while the other person has a cheap home made antenna mounted on a 10 foot pole that is at ground level and the terrain slopes upwards in all directions around him. These are just two examples in a myriad of possibilities. The best way to know for sure what the range of your transmitter will be is to set it up and try it out.