Radio waves

What are radiowaves?
Radio waves do more than just bring music to your radio. They also carry signals for your television and cellular phones. Cellular phones use radio waves to transmit information. These waves are much smaller that TV and FM radio waves.

What are the dangers of too much radio waves?
Large doses of radio waves are believed to cause cancer, leukemia and other disorders. Some people undeniably experience pain and other symptoms that those people attribute to their hypersensitivity to radio signals, but said there is no proof that radio signals are indeed the cause of the pain.

What is the difference between FM and AM on radios?
M stands for “frequency modulation” and AM stands for “amplitude modulation".
AM radio ranges from 535 to 1705kHz (kilohertz, or thousands of cycles per-second of electromagnetic energy). These are the numbers you see on your AM radio dial.

How far an AM station's signal travels depends on

1. The station's frequency (channel)
   
2. The power of the transmitter in watts
   
3. The nature of the transmitting antenna
   
4. How conductive the soil is around the antenna (damp soil is good; sand and rocks aren't)
5. Ionospheric refraction. (The ionosphere is a layer of heavily charged ion molecules above the earth's atmosphere.)

The FM radio band goes from 88 to 108 MHz (megahertz, or millions of cycles per second). Again, you can see these numbers on your FM radio dial.

To keep from interfering with each other, FM stations must be 200kHz apart within the same geographic area. However, since the signals of FM stations cover only limited distances, the same frequencies can be used in different geographic areas of the country.
First, these waves go in a straight line and don't bend around the earth as AM ground waves do. Thus, they can quickly disappear into space so the farther away from the FM or TV station you are, the higher you have to have an antenna to receive the FM or TV signal.
There's another problem: Since FM and TV signals are line-of-sight, they can be stopped or reflected by things like mountains and buildings. In the case of solid objects like buildings, reflections create ghost images in TV pictures and that "swishing sound" when you listen to FM radio while driving around tall structures.
Of course, the higher the FM or TV transmitter antennas are the greater area they will cover and this explains why these antennas are commonly very tall, or placed on the top of mountains. AM radio doesn't need that kind of advantage, since AM radio waves don't behave in the same way.

References:
http://news.techworld.com/green-it/3204279/radio-waves-may-be-dangerous-says-french-government/
http://science.hq.nasa.gov/kids/imagers/ems/radio.html
http://www.darvill.clara.net/emag/emagradio.htm
http://www.cybercollege.com/frtv/frtv017.htm
http://www.mentalfloss.com/difference/fm-vs-am/

Done by Michelle Dapito & Naveena Menon