What is FM Radio? How do FM radios work? and More…

What does FM mean in radio? FM, short for Frequency Modulation, is one of the few types of radio broadcasting in use today. As the name suggests it uses frequency modulation to give radio users high-fidelity sound over their device. High fidelity is a term used to define the high-quality sound reproduction offered by FM radio, which is in contrast to the lower quality of sound produced by AM radio. As a result of this FM has mainly replaced AM as the favorite broadcasting medium for music.

It was invented in 1933 by American electrical engineer and inventor Edwin Howard Armstrong, however, due to the domination of AM radio FM would rise to prominence way later in the early 1960s in the United States before spreading to most corners of the world.

Definition by FCC (Federal Communications Commission): “FM is short for frequency modulation, which refers to the means of encoding the audio signal on the carrier frequency. FM full power, low power, translator, and booster stations operate in the 88 – 108 MHz band. There are many classes of radio stations. The smallest provide service to areas within three or four miles of a transmitter site; the largest provides service to locations more than 60 miles from a transmitter site. Only non-commercial educational radio stations are licensed in the 88-92 MHz “reserved” band. Both commercial and noncommercial educational stations may operate in the “non-reserved” 92-108 MHz band.”

Definition by BBC UK: “FM, which stands for Frequency Modulation, is one of the radio broadcasting systems in the UK. FM uses frequencies from 87.5 MHz to 108MHz.

The BBC broadcasts a number of UK-wide network services e.g. Radio 1 and Radio 4. We also broadcast Nations’ services, e.g. Radio Scotland, as well as local services, such as Radio Bristol on FM. All FM services are broadcast in stereo and we can carry additional service data within the broadcast.”

How do FM radios work?

  • Broadcasting bands

A broadcast band is a radio frequency range that is used by broadcasters as their own radio channel. While the broadcasting band of FM is generally between 88 and 108 MHz (MHz – megahertz), it can vary between different parts of the world. For example in Western Europe, Africa, and Australia the range of 87.5 to 108.0 MHz is used, this band is called VHF Band II, while the United States of America and the rest of North America and the Caribbean use a similar range of 88.0 to 108.0 MHz. The range for Brasil and Japan is very different from the two already mentioned and ranges from 76.0 to 95.0 MHz. Also worth mentioning is the now obsolete International Radio and Television Organisation band which was once common on the eastern side of the Iron Curtain. Its range is defined as between 65.9 to 74.0 MHz. It started to be fazed out after the dissolution of the former Soviet Union with most former countries of the Warsaw pact using 87.5 to 108.0 broadcasting band.

The American Federal Communications Commission (or just FCC for short) has reserved the 88 to 92 MHz band for use only by noncommercial educational radio stations, which leaves the 92 to 108 band open for the operation of both commercial and noncommercial radio stations. While frequency modulation can be generated at any frequency it should be noted that all of the aforementioned bands belong to the VHF (very high frequency) range, which ranges from 30 to 300 MHz.

book: radio freqency modulation made easy
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Why is FM better than AM?

While FM and AM radios might seem like vastly different technologies they basically work the same way. Their difference comes due to the different ways their carrier waves are altered. The amplitude (its largest value) of the AM radio signal is varied to incorporate the sound information, while with FM the carrier signals frequency is varied.

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Even if booth AM and FM radio signals are susceptible to slight changes in amplitude, these changes result in static in the AM signal, while this doesn’t matter in FM broadcasting since the sound is conveyed through changes in frequency. This results in no static being created and shows why FM has become so dominant since its inception.

FM Transmission Power

The most important parameters which govern how far a broadcast transmission will cover are:

  1. The output power of the broadcasting transmitter. The power of the transmitter should be chosen as such that it doesn’t interfere with other stations while also being able to cover its assigned area. This usually ranges from a few milliwatts and up to 80 kW. It should be noted that the more powerful the transmitter is the more maintenance it needs.
  2. The height of the transmitter’s antenna. This one is pretty self-explanatory, the higher the FM antenna is the more area it can cover than an antenna that is somewhere lower.
  3. And last but not least is the antenna’s power gain. This parameter is gained by combining the antenna’s directivity, which is its concentration radiation patterns in a single direction, and electrical efficiency, which is the measure of which the antenna converts its radio frequency into radiated power.
book: FM Transmission and Reception Paperback – January 1, 1948 by John F. Rider (Author), Seymour D. Uslan (Author)
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FM reception distance

The reception distance of FM broadcasts does not, usually, exceed more than 50 to 60 km, as the very high-frequency radio waves do not travel far beyond the horizon. These waves can also be easily blocked by hills, mountains, and sometimes tall buildings. It is possible that a person with very sensitive radio receivers and/or specialized antenna systems can catch and listen to FM radio signals at greater distances. This would still be a lot less than the range of the older AM radio stations, which due to their lower frequencies, can travel thousands of kilometers. The reception distance of FM radio broadcasts heavily depends on the aforementioned parameters of FM transmission power: the output power, height, and power gain of the transmitter’s antenna.


  1. When did FM radio start
  2. How to improve the FM signal on the radio with a single wire antenna?

A short history of FM & Epilogue

What is FM Radio
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  • In North America

As we have already mentioned FM had its humble beginnings in the United States in the 1930s. Its inventor Edwin Howard Armstrong was also the first to start a regular broadcast using this new technology, with others soon joining. At first, they gained a small following but the potential was clearly there for all to see. The first broadcasting band was established in 1941 and it ranged from 42 to 50 MHz, another change happened in 1945 which moved the band to the 88 to 108 MHz range where it stands today. In the beginning, they were used for testing and broadcasting classical music, but a major shift happened in the tale end of the 1960s when an increasing number of stations switched to the rock which made their listener numbers increase rapidly until 1978 when FM finally took over AM by the number of radio stations.

Book: sounds of change - a history of FM broadcasting in America
Photo: amazon.com

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  • In Europe

In Europe the trend of adoption varied by country. German radio broadcasters were most eager to adopt this new technology since the occupying allied powers allowed them only two radio frequencies. The only way they could survive as radio stations is by adopting FM. Others in Europe were more conservative and adopted FM way later in the 1960s, 1970s, and even 1980s, like the United Kingdom and Ireland. In other countries seeing that their government is too slow for their liking in implementing FM radio ordinary people organized their own radio stations. These so-called ‘pirate radio’ stations sprung up all over Italy and Greece which forced the governments of these two countries to hasten the implementation of FM technologies.

  • In Oceania

The situation is totally different in Oceania. While experiments were conducted as early as 1946 FM radio did not catch on and even today AM dominates. Perhaps because AM radio has a longer reception distance allows the radio signal to reach more people in sparsely populated Australia.

If this section does not sate your curiosity when it comes to the history of FM radio then feel free to read our previous article that goes deeper into the beginnings of this wonderful technology: When did FM radio start.

The epilogue of what is FM radio

Even if we have only scratched the surface of how FM radios work, their history, or even what they are we hope that this article pleases you and at the same time motivates you to learn more about this wonderful medium of radio broadcasting.


  1. How can I find local FM stations?

The easiest way would be to find on the internet one of the many sites dedicated to giving users access to their locally found FM radio stations. For example, tunein.com is one such site.

  1. Why did it take almost three full decades for FM radio to catch up to AM radio in the United States?

It took a lot of time for the FM technology to receive its standard frequency. In fact, it had more changes in its first two decades of existence than in any other time of use. The dominance of the AM radio by the time FM was invented also did not help.