AM vs. FM Radio: Differences, Advantages, and Trends

Introduction:  For those of you who, like me, have always just accepted the fact that the difference between FM and AM radio is the amount of talking that goes on each station, it is time to broaden your amplitude of radio knowledge.  This simple comparison does not answer why.  Why is music predominantly played on FM stations?  Why do AM stations cover a broader geographic range than FM?  Why is there more static in AM stations than FM stations?   I will answer all of these questions in the following paragraphs.

Definitions:

To begin to understand the difference between FM and AM radio it is important to know what each stands for.  AM stands for Amplitude Modulation, meaning the wave that carries the message has a varying amplitude that the receiver (aka radio) uses to understand the sound information. Amplitude is the overall strength of the signal.   AM radio waves also have a smaller bandwidth size, 10kHz, meaning the range of frequencies available to AM radio are smaller in comparison to FM radio wave bandwidth.   A sample carrier wave for an AM transmission is shown below:

FM stands for Frequency Modulation and is represented by the image above.  Instead of amplitude, the frequency of the carrier wave is varied and the receiver interprets this to understand the sound information.  Frequency is the number of waves being received per second.  Bandwidth size for FM radio waves is much larger than AM, 200 kHz, allowing for a larger range of frequencies, more advantagious for music. 

Advantages:

AM    1.       The range that AM radio can cover is far superior to that of FM radio.  It accomplishes this mass transmission by refracting waves in the atmosphere.

                2.       AM radio waves are cheaper because they are less reliable.

FM     1.       FM radio presents a huge advantage over AM radio.  For one, because it doesn’t rely on varying amplitudes, it doesn’t get as much interference from weather conditions in the atmosphere that disrupt AM transmissions.

                2.       FM radio waves allow for the source to emit two channels of information simultaneously, allowing for left and right audio channels, perfect for stereo quality. 

Disadvantages:

AM    1.       AM radio has an increased susceptibility to weather conditions that distort the signal because the amplitude is what the weather conditions affect, which is where the signal is carried for AM waves.

           2.       AM radio only emits one audio channel, which is not ideal for stereo sound.

FM     1.       FM radio can only cover a range of about 50 miles.

Trends:        As you can see, FM radio is definitely more advantageous for playing music, while AM radio is more advantageous for talk radio.  In fact, AM radio’s broad geographic range is one of the reasons talk radio uses it more than FM.  The trend in the 1980s and 1990s in the United States for music stations was a switch from AM to FM radio stations because of the better sound quality.  Today, the number of FM radio stations far exceeds that of AM radio stations, 28,693 and 16,265 respectively.  However, it is also important to keep in mind the fact that the geographic range problem for FM radio stations may also have an effect on the number of stations needed to cover most areas. 

Reflection:  As it stands, clearly FM radio is more popular in the eyes of American radio broadcasters and American radio listeners.  As we discussed in class, music radio accounts for 70 percent of all radio formats, while talk radio and news accounts for only 13 percent of all radio formats.  Even if all talk radio and news stations were on AM radio stations, which they aren’t, FM radio clearly dominates with 70 percent, all of which are on FM stations.  Even WTOP, a news station that covers traffic and weather on the 8s, switched from AM radio to FM radio because “more people listen to FM radio”, according to Neil at WTOP.  Overall, the advantages of FM radio outweigh the costs of a shortened geographic range, while AM radio can’t seem to overcome its cost of reduced signal quality.