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What is the Difference between FM and AM Radio?


Before smartphones were invented, the easiest way to listen to music was to tune in your favorite radio station. A pair of batteries or electrical power was enough to get the device going. With an ‘FM’ or ‘AM’ modulator, and a volume regulator, you could remain entertained and receive news all-day.

Radios and FM stations are still relevant and popular globally. And unlike in the past, they are available on multiple devices. Their underlying technologies, AM and FM signals are still active and different as ever.

Below we review the main differences between the two kinds of radio waves, their strengths, and drawbacks in transmitting radio signals.

What are Radio Waves?

Radio waves are a type of electromagnetic radiation with frequencies as high as 300 GHz and as low as 30Hz. The waves travel at the speed of light. Sometimes lightning and astronomical objects can also transmit radio waves.

Artificial radio waves are used in many fields besides in AM and FM radio stations. They are used on communication satellites, wireless computer networks and for mobile radio communications. The waves have varying levels of strength. Long waves can diffract around buildings and mountains while short wavelengths only travel in the visible horizon.

In radio transmissions, signals are modulated to travel longer distances than they naturally can. Radio signals have low frequencies. But by being added to carrier signals that have long, constant waveforms, they are able to travel thousands of kilometers.

AM versus FM

Modulation happens in two major ways: amplitude modulation and frequency modulation. A third form called phase modulation carries data into alternating currents phase by phase. We’ll tackle the first two.

What is AM?

Amplitude Modulation (AM) dates back to the early days of radio waves. Scottish physician James Clerk Maxwell discovered wavelengths in 1867 but his theory didn’t come to light until in the 1890s. AM signals vary in proportions equal to those emitted by message signals.

In essence, they alter the amplitude of the signals sent over depending on the information sent. AM signals do not affect the frequencies. This also explains why some channels on AM radio appear weak but the sound largely remains static.

What is FM Radio?

Frequency Modulation (FM) is transmitted through frequencies as opposed to amplitude. Information is encoded and sent through carrier waves that only vary by frequencies. Compared to AM signals, FM waves produce less noise and lead to lower frequency interferences.

The difference in noise levels is very clear should you attempt to switch channels using either AM or FM. With the latter, the sound is cleaner and less noisy even when radio station signals are weak. As a result, almost all devices that transmit radio waves use FM signals.


Sound Quality

FM undoubtedly trumps AM signals when it comes to sound quality. AM signals are vulnerable to noise interference because of the way they are transmitted (amplitude). The fact that information sent over radio waves is stored in the amplitude doesn’t help.

By comparison, FM signals focus on frequencies, allowing them to transmit information with less noise interference. Surprisingly, AM isn’t obsolete yet and is used in many fields of science besides radio.

As a consumer, however, stick with FM and always buy the best FM antenna to improve the quality of radio signals in your house. They are inexpensive but make a huge improvement to the level of sound quality you receive on your radio devices.

Area of Reception

There is a reason why you can’t listen to your favorite music stations abroad. Radio waves are limited in how far they can be transmitted. FM signals have low reception coverage, which limits them to cities and neighboring areas. AM waves traverse cities and remote areas alike, reaching far more people than FM.

Radio waves are also regulated in every country. In the US, the Federal Communications Commission (FCC) regulates interstate communications made by cable, satellite, wire, radio and TV stations. With radio, each station is licensed to transmit their waves in certain regions only, failure to which they can be fined up to $250,000.

Equipment and Costs

AM has been around for more than 100 years and very little has changed in how it works. Its signals take up little bandwidth at 30 kHz. They can travel far and don’t have any complexities. This also makes them less complicated to install and overall cost friendly.

The equipment used to transmit FM signals, especially over long distances, can be expensive and complicated. The waves also consume more than double the bandwidth AM requires at 80 kHz. Transmitting the same amount of information through FM is often much more expensive than with AM.

Because of cost issues and other factors, best portable AM FM radios combine both AM and FM technologies but use them for different purposes. Some radios broadcast news through AM to reach more people but air music on FM to maintain high qualities.

Power Consumption

AM radios made sense back when electricity was costly and inaccessible in many areas in the world. Back then, you had to power your radio using cell batteries. AM didn’t and still doesn’t consume a lot of power, hence its popularity in remote areas.

By comparison, FM signals consume a lot more power than AM waves. The differences are not huge though, which is why your radio bills aren’t exorbitant. Whereas in terms of power consumption, jobsite radios consumes less power and has a special charge system that is designed to top up the battery very quickly.

Applications outside Radio

AM and FM may be popularity in radio but the signals modulate more than just radio waves. They are used for underwater communications by submarines, divers and support members. The signals used for this purpose are a subset of AM that transmits information through Single sideband modulation.

Another area radio transmission may be used is with radar and seismic communications that help scientists detect earthquakes before they happen. In hospitals, doctors monitor movements in unborn children thanks to frequency modulation. The modulations also help with music synthesis among other things.

To Conclude

AM and FM radio waves are widely popular around the world despite the emergence of newer, improved communication technologies. AM came before FM and transmits information by altering the amplitude aspect of the signals. FM alter the frequencies, which make the signals cleaner and less noisy.

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