An FM transmitter broadcasts a signal in the frequency range 88-108 MHz. The transmitting antenna emits the electromagnetic waves that carry the signal.
The coverage of an FM transmitter and its antenna system is determined by the power of the signal and the sensitivity of the receiver.
In general, an FM transmitter with a higher power output will have a greater coverage than one with a lower power output. Another important factor is the operating environment. FM signals will travel further in rural areas than in a city.
To calculate how far the FM signal will travel enter the Transmit power in either dBm or Watt. As well, select the propagation environment.
Formula
The antenna range calculator can be used to determine the path loss between two antennas. The path loss is the amount of power that is lost as a signal travels from the transmitter to the receiver. The calculator takes into account transmitter and receiver antenna gains and the distance between them. It uses the free space path loss equation:
FSPL = 20*Log10(d) + 20*Log10(f) + Lc + 20*Log10(4π/c) – GTx – GRx
The Free Space Path Loss calculator however assumes ideal conditions of free space.
This Range calculator by comparison uses ITU receiver sensitivity estimates that are consistent with three different environmental conditions
- Rural
- Urban
- Large City
Example Calculation
An FM transmitter with an output power level of 1 Watt or +30 dBm has a range of 11 kilometers or 7 miles in a rural setting.
The same power level is able to reach only 1.1 kilometer or 0.7 miles in a large city. in other words, the range is only 10% in a congested environment on account of large buildings and other obstructions.
The table below summarizes distance covered by a 1 Watt FM transmitter
| Environment | Kilometers | Miles |
| Rural | 11.1 | 6.9 |
| Urban | 2.8 | 1.7 |
| Large City | 1.1 | 0.7 |
Example Calculation
According to the ITU, the following table shows required sensitivity in dBuV/m for FM in various environments. We have used the dBuV/m to V/m calculator to convert the units.
| Environment | Field Strength (dBuV/m) | Field Strength (V/m) |
| Rural | 54 | 0.0005012 |
| Urban | 66 | 0.0019953 |
| Large Cities | 74 | 0.0050119 |
The field strength is used to calculate the input power at the receiver in dBm using the V/m to dBm Calculator. In this case the antenna gain of 0 dBi is used. However you can substitute any value in this calculator.
The FM frequency range is 88-108 MHz.
| Environment | Field Strength (V/m) | Power (dBm) |
| Rural | 0.0005012 | -64 |
| Urban | 0.0019953 | -52 |
| Large Cities | 0.0050119 | -44 |
Summary
The FM range calculator provides an estimate of the distance that an FM signal can travel. It is useful for RF planning purposes. For instance you can use it to calculate whether you will be able to receive an FM signal that is a known distance away.
Related Calculators
- 1000 Watt FM transmitter range
- 15 Watt FM Transmitter range