What is FM trasmission ?

FM technology is ideal for broadcasting in a local area at a relatively low cost.

FM is known as a ‘line of sight’ radio signal. This means that the signal from the transmitter and antennae is clearest if the receiver is within the sight of the antennae. If the terrain is flat the signal will be strong at close range and travel out with decreasing clarity. If the terrain is hilly, the hills will tend to block the signal create what are known as shadows in which is reception is unclear or not audible at all.

The strength of transmission (also known as ERP or effective radiated power) depends on various factors: the power and quality of the transmitter and the number and height of the antennae.

In general, the higher the antennae, the stronger the signal. Most antennae are mounted on a tower Antennae can be uni- or omni-directional, meaning that they can send signals in a specific (uni) direction or to all (omni) directions.

Most small FMs use two or four omni-directional antenna elements. Adding more elements will increase the strength of the signal.

Small local FM radios generally use a transmitter with power in the range of 30 to 500 watts, although power of 1000 or even higher is also possible. The cost of the transmitter increases with the power. In an area without major geographic barriers like hills or mountains, a 100-watt transmitter will provide a strong signal in a 20-kilometre radius.

The transmitter and the antennae are linked using special coaxial cable which is expensive, meaning that the distance from one to the other is an important consideration.