Why does AM radio sound so poor compared to FM radio?

Question

I do not understand why the fidelity of AM radio is so poor compared to FM radio. In theory, there should be no difference, I believe.

Answer 1

When discussing the effectiveness of AM vs. FM, you have to understand the affect of Attenuation.

When radiation (Radio waves are a form of radiation) travels through any material, it loses energy. This is known as Attenuation.

Now, AM is amplitude modulation, and FM is frequency modulation. This means that the information being sent (music, sports talk, or an over-zealous evangelist) is 'encoded' or modulated over a base 'carrier' wave. In the case of AM, the amplitude of the carrier wave is changed, whereas in FM, the frequency is changed.

The reason why AM sounds so much worse, is due to the information being lost. When a particular 'piece' of radiation is attenuated, one of two things happen:
1) It is absorbed completely
2) It loses some energy

Absorption would affect AM and FM equally. However, the degradation of AM comes when the radiation field loses energy. What part of the wave gives up this energy? The Amplitude of the wave represents the energy of the particle (photon, in this case).

As an AM signal loses energy, it's amplitude changes, which makes the signal different from when it was first sent.

As an FM signal loses energy, it's amplitude changes as well. Since the information is stored in the frequency changes, this signal remains the same (just as crisp and clear), but the strength of the signal drops.

Answer 2

AM stands for amplitude modulation, which means that the amplitude of the signal stores the information. Noise is added to all forms of communication, and is additive, which directly effects the amplitude, thus causing distortion and hurting the fidelity of the signal.

FM stands for frequency modulation, where the frequency is changed to pass information. Since the the tuner or radio filters much of the noise caused by other frequencies, and the added noise mostly effects the amplitude (which has very little effect on the frequency), FM does not get as effected by the noise.

If you are interested in the best fidelity of radio, look into HD radio, which is digital signals passed on the same FM bands, this is digital radio, which will produce no distortion, giving you CD quality radio. XM and Sirus radio are also digital signals, but are based on different frequencies and sourced by satellite and local repeaters. (plus you'll have to pay for XM or Sirus service)... HD radio is free, and will eventually replace the analog FM we all use now.

Answer 3

The quality of all types of communication comes down to SNR (signal to noise ratio). FM has a higher SNR than AM, under similar conditions. In the absense of noise, i.e. your imagination, they will produce the same quality signal.

There are types of modulation that produces a higher SNR than FM, but FM is good enough so they didn't pick up.

If you don't believe, then try this test. The next time your favorite song comes on the FM dial, have the same song in your CD player. Flip back and forth from listening to it on the radio and from the CD player. The CD player will sound better because of the higher SNR.

Answer 4

AM is "amplitude modulated" radio where as FM is "frequency modulated".

The main reason FM sounds better is because it can be broadcast in stero and AM cannot. As well, the amplitude modulation allows for interference to sound like static without completely washing out the signal as it can in FM.

Answer 5

AM stands for Amplitude Modulation where FM stands for Frequency Modulation.... AM is not able to travel the same distance as FM becuase of the way the signal waves travel, which is why is sounds poor unless you are very close to the tower.

Answer 6

Am has to do with the size of a radio wave, fm has to do with the frequency or speed of the radio wave.

Fm comes in sterio, and AM is in mono, AM is a much older technology.

Answer 7

DAB had its reward, besides the undeniable fact that the signal is there or it truly is not. Even the slightest stream can decrease to rubble what's meant a more desirable physically powerful signal. digital television is overvalued, and there are too many blocks appearing on the television demonstrate to make something watchable.

Answer 8

AM use variation in amplitude to define the information and most of noises caused by another equipment(motors, machines,storms.....) put another amplitude to our signal so we receive signal & noise but in FM we use frequncy variation and in recieving we can cut additional amplitude(caused by noise achieved in signal way) result in pure singnal(for YOU)