What Is the Difference Between AM and FM Radio?

what actually is the difference between AM and FM radio?

Both are methods of encoding and broadcasting radio signals. The difference is how they do that. Radio signals travel as electromagnetic waves — invisible to us, but as fast as the speed of light, and on the spectrum of electromagnetic radiation.

Now, this is where it starts to get a little confusing. And it’s got to do with the words we use.

Radio waves are around us all the time, but we can’t detect them on our own. They are a long-wave form of electromagnetic radiation. So, more confusingly, radio waves are part of the same spectrum as light, not sound! That’s why they travel as fast as light.

Mechanical and Electromagnetic Waves

Radio waves can’t be “heard” and have nothing to do with sound waves. Soundwaves are sound waves and they move through air, water, and even solid surfaces, but they need to be able to move the particles of that medium; and transverse waves move through water and other media in perpendicular oscillations.

On the other hand, electromagnetic waves — the types of which include light, microwaves, infrared, x-rays, ultraviolet, and radio — do not require a medium through which to travel. That’s why they can move through deep space and through physical barriers.

Transmission and Reception

Radio waves surround us all the time, but the only way we can pick them up is with a radio receiver. The term radio also refers to the technology that allows information to be transmitted and received over radio waves. You can have individual pairs of transmitters and receivers that come together, like two-way radios or walkie-talkies, or one-way broadcasts from a single powerful transmitter to multiple receivers, which is like the giant radio towers in your city and the tiny radio in your living room.

Differences in Sound Quality

The difference in the way AM and FM radio signals are encoded means differences in sound quality, performance, and broadcast range between the two types of station. This explains why FM stations sound better than AM stations, but AM stations can be heard from further away.
AM radio varies the amplitude of the broadcast signal so the power at which that signal is broadcast is also changed, since amplitude represents the strength of the signal. Some receivers can’t pick up low amplitude signals at all. FM radio, always remains at constant amplitude, so signal strength does not change.

FM uses a higher frequency range and a bigger bandwidth than AM. AM radio operates from 535 kHz (kiloHertz) to 1605 kHz. When you tune the dial on your radio, the number changes by 10 kHz each time. This means that each station has 10 kHz of bandwidth on which to broadcast. FM radio on the other hand operates between 88 MHz (MegaHz) and 108 MHz, and your radio increments every 200 kHz.

Each FM station is allocated 150 kHz of bandwidth, which is 15 times that of an AM station. This means that an FM station can transmit 15 times as much information as an AM station and explains why music sounds so much better on FM. Since music has more electrical information contained within it than a monophonic voice audio signal, FM typically broadcasts music and AM generally sticks to talking programs.

The trade off for AM radio, though, is that the lower frequency band means that it has a larger wavelength and therefore a much longer broadcast range. If you think about important information that has to be broadcast out to a wide range of citizens, like traffic or weather warnings, or government announcements, AM is still the way to go. (Although if the information is urgent enough, it will likely be transmitted in as many places as possible.) That’s the reason Radio New Zealand National (AM) is our designated Civil Defense lifeline utility radio broadcaster.

In addition, the larger wavelength waves of AM also travel very well through solid objects, like mountains! Higher frequency FM radio waves don’t do so well here. Lastly, despite AM radio’s potential for increased interference from natural radio waves, particularly solar, it is actually theoretically possible for an AM broadcast to be heard right around the world.

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