Radio, in which parameter is the information?

[Helicobacter]

When I listen to radio, then I know that the radio gets the information from electromagnetic radio waves. But in which parameter is the information of the song/news/output/whatever included?

It can't be amplitude, since amplitude decreases with distance of obstruction, and the data most people receive is relatively identical.

it can't be frequency/wavelength, since every channel has a constant frequency assigned to.

 

[rachmaninoff]

http://en.wikipedia.org/wiki/Modulation
http://en.wikipedia.org/wiki/Amplitude_modulation
http://en.wikipedia.org/wiki/Frequency_modulation

It can in fact be in the ampliutude or frequency. Think relative amplitudes, and small variations in frequency.

Some other modulation schemes are listed in the first link.

 

[jtbell]

it can't be frequency/wavelength, since every channel has a constant frequency assigned to.

In the USA, each FM channel actually spans a frequency range of 0.2 MHz. For example, a station that broadcasts at 90.1 MHz actually uses frequencies between 90.0 and 90.2 MHz.

http://www.fcc.gov/mb/audio/bickel/oddno.html

The diagram on that page has a typographical error. FM Channel 202 should be labeled as 88.3 MHz.

 

[DaveC426913]

AM = amplitude modulation
FM = frequency modulation

Remember that the radio freq is a carrier wave. This means that the (AM)680kHz wave or (FM)107.1 MHz wave is modulated to provide a much lower normal humans range signal riding on top.

FM = the frequency of the carrier is modulated to carry sounds in the normal human range
AM = the amplitude of the carrier is modulated to carry sounds in the normal human range