Defining Your Radio Stations

So FM and AM radio are different, so what? Well, first a quick lesson about how radio works. A microphone converts sound waves into electrical waves. On the receiving end, a speaker converts the electrical waves into wound waves, usually with the help of an amplifier. In between, invert a radio transmitter and a radio receiver. Below is a simple diagram of how a radio works:

AM stands for Amplitude Modulation and FM stands for Frequency Modulation. You know all those numbers before "AM" and "FM"? Since radio waves are light waves, they stand for the Hertz of a wave. AM radio stations stand for a certain number of kilohertz and FM radio stations stand for a certain number of megahertz. For and example, 720AM is 720 kilohertz and 80.5FM is 80.5 megahertz. Radio waves are modulated, meaning the sound is encoded on the carrier wave so that the original sound can be detected by the receiver. 

In AM radio, the amplitude of the carrier is modulated by the electrical version of the signal, as seen on the left. However, most sound signals are not a smooth sine wave like the one in the diagram, they are much more complicated, like the silhouette of a mountain range. Then, it becomes difficult to "retain" the shape of the signal, as the AM wave would need to increase the amount of "bumps" in the wave to get all the details. There is a limit to the audio quality. 

This is where FM comes to play. FM radio modulates the frequency, like compressing a spring. FM radio can handle a larger range of sound (88-108 megahertz) compared to AM radio (.535-1.705 megahertz). This is why FM radio stations have better sound quality. 

On the other hand AM radio waves can travel long distances due to ionospheric refraction. The waves reflect off the ionosphere, a layer of heavily charged ion molecules above the atmosphere, and the ground. This is beneficial for long distance communication. However, this process is much more effective at night, so "at sunset most AM radio stations in the U.S. have to reduce power, directionalize their signal, or go off air."

FM radio waves are not effected by the ionosphere and their waves appear to go in a straight line. The benefit is that FM stations do not interfere with each other. However, because their signal will not "bend around earth" as much as AM waves, their signal cannot be heard as far from the station. Their "line-of-sight" waves can be disrupted by solid objects like buildings and mountains. FM transmitter antennas are usually taller, to cover a larger area.

FM radio was created after AM radio by Major Edwin Armstrong who changed how radio signals were transmitted. Unfortunately, he never was able to see its success. After long money draining legal battles trying to promote his superior radio system against David Sarnoff and RCA (Radio Corporation of America), he committed suicide January 31, 1954. After Armstrong's death, FM radio has increased in stations and listeners and has passed AM radio.

Next time you listen to the radio on the car, depending on if you are listening to FM or AM, see if you can hear "swishing sounds" due to large buildings or the decrease in clarity when nightfall hits. Happy listening!