Why Do Cars Have More FM Stations Than AM? The Science Explained

Radio has been a part of our lives for a long time, bringing us news, music, and entertainment. Even though we have lots of other ways to listen to things now, like streaming services, traditional radio is still pretty popular, especially in cars. You’ve probably noticed that your car radio has both AM and FM stations. But why do cars usually have more FM stations than AM?

To understand that, we need to get a little technical about how AM and FM radio work. They’re both ways to send sound through the air, but they use different methods. Let’s dive into the details

What is AM and FM Radio?

AM (Amplitude Modulation) and FM (Frequency Modulation) are two methods of encoding information onto a radio signal for transmission. Both methods involve altering a carrier wave to send audio content (like music, news, or talk shows) over long distances.

1. AM Radio:

Modulation: In AM radio, the strength of the carrier wave, or its amplitude, is changed to represent the audio signal. It’s like adjusting the volume of a sound to match the music or voice. The higher the sound, the stronger the amplitude.

Frequency Range: AM radio uses a lower frequency range than FM, typically from 530 kHz to 1700 kHz. This lower frequency range helps AM signals travel farther, but it also makes them more vulnerable to interference.

2. FM Radio:

Modulation: FM radio uses frequency modulation, which means the frequency of the carrier wave is changed to represent the audio signal. This is different from AM radio, where the amplitude (strength) of the carrier wave is changed.

Frequency Range: FM radio operates at a higher frequency range than AM, typically from 88 MHz to 108 MHz. This higher frequency range contributes to FM’s superior audio quality and reduced susceptibility to interference.

How Are AM and FM Signals Generated?

Both AM and FM radio start by turning sound (like a voice or music) into an electrical signal. This electrical signal is then combined with a special “carrier wave,” which is like a base signal for the information. 

In AM radio, the amplitude, or strength, of this carrier wave is changed to match the changes in the audio signal. Think of it like turning a knob up and down to match the volume of the sound. This modified signal is then sent out through an antenna.

In FM radio, the frequency, or pitch, of the carrier wave is changed instead of the amplitude. This means the carrier wave is constantly changing its frequency to match the audio signal. It’s like changing the pitch of a sound to match the music or voice. This modulated signal is then also sent out through an antenna.

How Do We Hear AM and FM Radio?

To listen to AM and FM radio, we use special receivers called radios. These radios are tuned to pick up the specific frequencies that radio stations broadcast. They receive the electromagnetic waves sent out by the stations and decode the information encoded within those waves, whether it’s amplitude modulation (AM) or frequency modulation (FM), turning it back into sound that we can hear.

AM radio signals have a longer wavelength, which allows them to travel farther, especially at night. However, this also makes them more susceptible to interference from electrical devices, weather, and even natural factors like the ionosphere. 

FM radio signals have shorter wavelengths, making them less prone to interference. This means they generally have better sound quality, with less static and better fidelity. However, because of their shorter wavelength, FM signals don’t travel as far as AM signals, especially when they encounter obstacles like tall buildings or mountains.

Why Do Cars Primarily Feature FM Radio?

Modern cars favor FM radio primarily because of its superior sound quality. FM offers clearer, more dynamic audio with minimal interference, making it ideal for listening in a car. Whether you’re enjoying music, talk shows, or news broadcasts, FM’s higher frequency range delivers better fidelity, reducing static and noise, and improving the overall listening experience.

On the other hand, AM radio, despite its ability to reach greater distances, is more susceptible to interference. In urban areas or places with numerous electronic devices, AM signals often become filled with static, making it difficult to enjoy clear audio. Furthermore, when driving at high speeds, AM signals are prone to distortion and loss of signal. The rise of electric cars exacerbates this issue as their electric motors can generate electromagnetic interference, further impacting the quality of AM radio reception.