The radio portion of the electromagnetic spectrum has been divided up by governments to regulate who has the right to use different radio bands. Information, entertainment, military communication, weather, cell phone etc all share the spectrum. 

Transmission of information through radio waves is done by first encoding the waves using different methods and transmitting the encoded waves using transmitters and antennas. Receivers intercept the radio waves and decode the information so that it can be understood. 

There are different means of encoding information onto radio waves including amplitude modulation (AM), frequency modulation (FM), single side band (SSB), and continuous wave (CW). Two methods of encoding we will examine in this lesson are AM and FM transmissions.

FM radio was invented by a man named Edwin Armstrong in order to make high-fidelity (and static-free) music broadcasting possible. He built the first station in 1939, but FM did not become really popular until the 1960s. 

If aliens were attempting to communicate with us using radio waves, we would have to understand how they are encoding their information. If they are using the same types of encoding that we humans use, that would be relatively easy with only the language of their communication left to decipher. But if they had a method of encoding that we had not discovered yet, the message would remain incomprehensible, if we even recognized it at all as communication with us. 

1. Why does an AM station sound different from an FM station?