What's the difference between AM and FM radio?

Question

And what are the advantages and disadvantages of both?

Why is FM more popular?

Answer 1

It depends on the wave.

They are both different wave types, FM is preferred because it can hold more information.

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Answer 2

There's two things here to talk about, AM and FM broadcast bands, one versus the other, and what AM and FM are.

The frequencies in use have different properties. The AM broadcast band is bothered more by electrical disturbance like lightning and electric motors. Signals in the AM band are generally sent via ground wave, the follow along the curvature of the Earth until the signal is absorbed. It gives them the ability, with enough power, to travel long distances. The FM band is fairly strictly line of sight. Depending on the height of the transmitting antenna the signal can only travel to the horizon.

AM stands for Amplitude modulation. That is, the strength of the signal, its amplitude, contains the intelligence. As audio gets louder the signal strength increase with it. The signal has a carrier frequency, as audio shifts in frequency the modulation shifts the signal up and down from the carrier by that frequency. For example a radio station on 1000kHz, with an audio tone of 350Hz will produce a signal at 1000.350 and 999.650 kHz. These two signals are what are known as sidebands, there's an upper and lower. The strength of that signal is related to how loud that audio tone is.

FM is frequency modulation. Here the signal is full strength all the time. Again we have a carrier frequency. Let's assume a station in on 99.9MHz. As audio is applied the frequency shifts up and down, but unlike AM, it shifts in relation to the loudness. The stronger the audio, the farther the frequency shifts. The audio frequency determines the rate at which the shift occurs.

Now, by the nature of FM, because the receiver responds to changes in frequency instead of amplitude, FM is more resistant to electrical interference. So in addition to the frequency range used, the modulation is quieter. So FM generally offers a lower background noise level.

Next is bandwidth. FM, because it's the rate of change that determines frequency, can deliver a very high frequency response is less bandwidth than AM. In the USA AM broadcast stations are limited to 10kHz audio bandwidth, which uses 20kHz of radio bandwidth. FM stations can go out to 15kHz audio.

Over the years FM has been used for higher fidelity content versus AM. FM is also more resistant to interference from other stations, due to the nature in which the receiver works. AM signals mix easily, FM do not.

FM is not always more popular. It depends on the stations in your area. AM is still widely used. News, sports, talk, are popular on AM because the high fidelity is not required.

One does not travel farther than another. It is almost exclusively the properties of the frequencies in use that determine how and how far a signal will travel. FM would function on the AM broadcast band, and vice-versa.

Answer 3

First you have to understand radio waves, which are like waves on water.  Now, AM stands for amplitude modulation, which means that the radio waves vary by height, not frequency.  FM stands for frequency modulation, which means more or fewer cycles per second, but the wave height stays the same.  AM can travel over longer distance because you are not changing the frequency, but you lose the sound quality of FM.  AM is also more succeptible to atmospheric influences on the amplitude of the radio wave.  FM produces a better sound because of the higher frequency of radio waves.  FM requires more energy to maintain the cycle rate, so the range of FM is not nearly as far.

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