FM
Also called: frequency modulation
FM is an abbreviation for frequency modulation and is the designation for a frequency band and a means of transmitting radio signals.
How does an FM signal work?
The sound of a radio station is converted by a transmitter mast into signals that can be picked up anywhere within range of the mast. Electromagnetic waves are used in this process. These waves or vibrations are expressed in the unit Hertz (Hz). These signals are not visible or audible to us but can be converted back into the original sound using a radio (or other device with a radio antenna).
In frequency modulation (FM), tones are converted into slow or fast moving (modulating) radio waves. The faster/quicker a wave repeats itself, the higher the tone sounds. This is in contrast to amplitude modulation(AM), where the tone is represented by the amplitude of the vibration. FM signals are less susceptible to interference than AM signals. Also, the quality of the sound coming out of your radio is higher, making it more similar to the original recording.
What are FM frequencies?
The airwaves (the space available for radio traffic) are divided for different purposes. FM signals from radio stations use frequencies between 87.5 and 108 MHz. The bandwidth of one FM frequency is 200 kHz and the range of one FM transmitter is a maximum of 80 kilometers. Because of this limited range, rural radio stations rely on the use of multiple frequencies.
Radio stations are not allowed to decide for themselves what frequency they want to be received on. To broadcast on an FM frequency, the station must have a license. The FM band is divided into a large number of lots, distinguishing between national, regional and local broadcasters. Several of these lots are clauseed, meaning that conditions are imposed on the type of music and format of programs that may be broadcast.
FM frequencies are allocated in the Netherlands by the Netherlands Radiocommunications Agency (AT). These licenses can be obtained through a frequency auction or by taking over an existing station including a license. Frequency auctions are only organized when frequency lots become available. This can be due to the expiration of FM licenses or when a station stops operating. The last large-scale frequency auction was in 2003, at the same time as a large-scale reconfiguration of the airwaves.
Successor to FM: digital radio
DAB (Digital Audio Broadcasting) has been on the air since 2004, which should eventually replace FM, succeeded by DAB+ in 2012. This technology has its own frequency band, within which signals are transmitted digitally. Thanks to the compression applied, a higher number of stations can be received via DAB+ than via FM. The sound quality of digital radio is also better than with FM. In order to receive stations broadcasting on DAB+, a radio that supports this technology is required.
