AM vs FM Radio Explained: What’s the Difference?

Let’s take a quick trip back in time to a world without Spotify, Apple Music, or YouTube — back to the early 20th century. It was the time when physicists were experimenting with electromagnetic waves and inventors were creating the first radio wave receivers. It was the advent of AM (amplitude modulation) radio as we know it today. Since its inception, it’s been bringing people together to share news, music, and other broadcasts.

In the 1930s, FM, or frequency modulation, was introduced as an alternative to AM. As time went on, these two types of radio waves became more and more popular. Today, they are the two main types of radio broadcasting services.

AM and FM radio are two sides of the same coin, both providing us with endless hours of entertainment and information. But what makes them different? Is one better than the other? In this article, we’ll dive into the world of radio waves and signal modulation and make a one-to-one comparison of AM vs FM radio to see how they stack up.

AM vs FM Radio: Side-by-Side Comparison

AM vs FM Radio: What’s the Difference?

Now that we have an overview of their differences, let’s dive deeper into each one individually to understand them better.

Signal Modulation

The difference between AM and FM lies mainly in how information is encoded, in a process called modulation, onto electromagnetic signals. AM radio works by varying the amplitude of a radio wave to carry the audio signal. The audio signal is superimposed on the carrier wave’s amplitude, causing the wave to fluctuate up and down in strength.

The receiver then picks up these fluctuations and converts them back into an audio signal. AM radio waves can travel long distances but are more susceptible to noise and interference, which can cause static and distortion in the signal.

FM radio, on the other hand, works by varying the frequency of the radio wave to carry the audio signal. Information is superimposed on the carrier wave’s frequency, which causes the wave’s frequency to fluctuate accordingly. FM radio waves carry more information and provide higher signal quality than AM radio.

Frequency Band

AM waves are sent between 535 to 1605 kHz, while FM waves oscillate between 88 and 108 MHz. This variation means that AM waves are a better choice for long-distance communication, as they can travel farther compared to FM waves, which have a shorter range.

The reason for this difference is that lower frequencies tend to have longer wavelengths and can penetrate buildings, mountains, and other obstructions more effectively.

However, AM waves aren’t always the better choice. Their lower frequency also makes them more vulnerable to interference and noise from other electronic devices, including power lines, motors, and other electrical equipment. This interference can be frustrating for listeners, especially in urban areas with a high concentration of electronic devices.

In contrast, FM waves operate at higher frequencies, resulting in a shorter wavelength and more stable signals. As a result, FM radio stations can broadcast higher quality, clearer sound and are less affected by interference, making them the preferred choice for local radio stations.

Wavelength

As we mentioned earlier, the wavelengths of AM and FM waves differ, and this has a significant impact on the quality and reliability of the signals. Wavelength is simply the distance between two corresponding points on adjacent waves, such as the distance between the peaks or the troughs of the waves.

In the case of AM waves, the wavelength is much longer than FM waves, measuring between 600 and 300 meters. This means that the waves have a lower frequency, and therefore less information can be carried.

FM waves, on the other hand, have a much shorter wavelength, between 3 and 10 meters. This makes them capable of carrying more information, resulting in better sound/ signal quality.

Range

The range of a radio wave depends on its wavelength. With wavelengths between 600 and 300 meters as we’ve seen, AM waves can travel further without being attenuated (losing signal strength). This makes AM radio a better choice for long-distance transmissions. This can be advantageous for listeners in rural areas, as they may not have access to other forms of media.

AM waves travel farther due to the ionosphere’s reflection. This allows them to reach around the world without boosters, unlike FM waves which dissipate into space. However, this increased range also makes AM radio more prone to interference from other devices, such as other transmitters and power lines.

Signal Quality

When comparing AM vs FM radio in terms of signal quality, FM typically comes out on top. This is because FM radio is capable of transmitting a wider range of frequencies due to its higher bandwidth.

The higher bandwidth allows for more information to be carried, which results in a clearer and more detailed sound. The range of frequencies that FM radio can transmit also means that it can pick up more subtle nuances in music and speech, resulting in a more accurate reproduction of sound.

On the other hand, AM radio has a lower bandwidth, which limits its ability to transmit a wide range of frequencies. This results in a less detailed and clear sound quality, which is why AM radio is often used for talk radio and news broadcasts.

Despite its limitations, AM radio is still a popular medium for long-distance communication, especially in remote areas where FM radio signals may not be available.

It’s also worth noting that the quality of the signal received can be affected by several factors, such as the strength of the input signal, the quality of the equipment used to transmit and receive the signal, and the environment in which the signal is being transmitted. 

Resistance to Interference

FM radio trumps AM radio when it comes to resistance to interference. This is because FM radio’s frequency modulation is less susceptible to interference than AM radio’s amplitude modulation.

In simpler terms, FM radio’s method of encoding information into the carrier wave’s frequency means that any interference in the wave’s amplitude won’t affect the transmitted information.

This results in clearer and more reliable sound quality, with less distortion and noise. AM radio, on the other hand, encodes information into the amplitude of the carrier wave, making it more vulnerable to interference. This can cause static, crackling, and other unwanted sounds that can interfere with the listening experience.

AM vs FM Radio: Where Is Each Type Applied?

As we’ve seen, AM and FM have distinct characteristics that make either inherently more suitable for certain content. AM radio has long been the go-to for talk radio and news broadcasts, thanks to its ability to cover a larger range and lower susceptibility to interference.

This is particularly useful for emergency announcements and public service messages that need to reach a wide area quickly. AM waves travel farther than FM waves due to their reflection off the ionosphere.

This allows them to reach more distant locations without the need for terrestrial boosters. Additionally, AM waves easily move past many physical obstacles, making them ideal for emergency communication. AM radio is also generally more accessible, with a larger number of low-cost receivers available.

FM radio, on the other hand, has traditionally been the preferred choice for music broadcasts because of its lower susceptibility to noise and superior sound quality, which is essential where fidelity and clarity are imperative to the end listener’s experience.

Over time, the distinction between AM and FM radio has evolved, with most radio stations now using FM for talk shows and news programs due to advancements in technology that have improved sound quality.

Nonetheless, the traditional use of AM and FM radio still holds true in some places, with AM radio often serving as the primary source for talk radio and news, and FM radio as the top choice for music broadcasts.

AM vs FM Radio: 6 Must-Know Facts

1. James Clerk Maxwell predicted radio waves in 1864, which Heinrich Hertz discovered in 1888. Hertz earned the honor of having the unit for frequency named after him in recognition of his work.
2. Both types of radios use electromagnetic radiation which travels through air at light speed (300 million meters per second).
3. Reginald Fessenden was the first person to broadcast an audio signal using amplitude modulation (AM) on Christmas Eve 1906 from Brant Rock Massachusetts.
4. In 1933, Edwin Armstrong demonstrated wide-band FM using a prototype transmitter he had built himself out of spare parts he found lying around his lab at Columbia University.
5. In order to receive an AM signal, you need an antenna that can pick up long-wave signals; however, in order to receive an FM signal, you need an antenna that can pick up short-wave signals or use a satellite dish if you’re using satellite radio services such as SiriusXM.
6. Cheap, consumer-grade walkie-talkies typically use amplitude modulation (AM), while more costly professional-grade ones usually employ narrow-band frequency modulation (FM).

AM vs FM Radio: Which One Is Better?

When it comes down to it, the decision of whether to use AM or FM radio usually depends on the situation at hand.

For long-distance communication, AM radio is typically the better choice, as it can travel farther and penetrate walls and other obstacles more effectively. However, due to its lower bandwidth, it’s more susceptible to interference from other signals, resulting in static and distortion.

On the other hand, FM radio is the preferred choice for local radio stations, providing higher quality sound and being less affected by interference. However, its shorter wavelength limits its range, making it less suitable for long-distance communication.

Ultimately, the choice between AM and FM radio comes down to the specific needs of the broadcaster and the intended listener, and the environment in which it’s being used.

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