Below are the approximate range of different power FM Transmitters.
0.1W ~ 5W FM Transmitter :100M ~1KM 5W ~15W FM Transmitter : 1KM ~ 3KM 15W ~ 80W FM Transmitter : 3KM ~15KM 80W ~500W FM Transmitter : 10KM ~30KM 500W ~1000W FM Transmitter : 30KM ~ 50KM
NOTE:
Connect antenna first ,then connect the power supply, otherwise, transmitter will be burned out.
Select an unused FM station in your area ,adjust any FM Radio to the signal that your are broadcasting on.
Package includes:
1*150W RS RADIO 150 FM Transmitter
Q&A:
How far(long) the transmitter cover? The transmission range depends on many factors. The true distance is based on the antenna installing height , antenna gain, using environment like building and other obstructions , sensitivity of the receiver, antenna of the receiver .  Installing antenna more high and using in the countryside , the distance will much more far.
EXAMPLE 5W FM Transmitter use in the city and hometown:
I have a USA customer use 5W fm transmitter with GP antenna in his hometown
and he test it with a car, it cover 10km(6.21mile).
I test the 5W fm transmitter with GP antenna in my hometown ,it cover about 2km(1.24mile).
I test the 5W fm transmitter with GP antenna in Guangzhou city ,it cover about only 300meter(984ft).