Radio wave

A radio wave is an electro magnetic wave. We modulate them using three different modulations, frequency modulation, amplitude modulation, and pulse modulation, to carry information.

http://www.howstuffworks.com/radio5.htm

For frequency modulation slight variances are made in the frequency of the wave to represent different bits of information. This is widely used because it is less likely to have static.

 

For amplitude modulation the height or amplitude of the wave is changed to contain information. Amplitude modulation is not only used by radio stations but it is also used to send the picture part of television.

 

Pulse modulation is where there are breaks in the wave to indicate the desired information. This is usually used for morse code but can be used for a few other things as well.

 

propagation

According to maxwell's equations radio waves travel at the speed of light. The magnitude of a wave will decrease at a rate of r^2. Where r is the distance from the origin. This is because the wave is propagates in all directions so the same amount of energy spreads out over a greater area.

But how can we get signals from beyond the horizon? Today we could use satellites, but you can also bounce a radio wave off of parts of the upper atmosphere. This can be done because the sun ionizes levels of upper atmosphere. an electromagnetic wave resists crossing these layers.

http://www.arrl.org/tis/info/images/MagneticField.jpg

This is an illustration of how charged particles can affect a magnetic field. the distortion of the magnetic field around the earth is caused by solar winds, which are comprised of charged particles that are emitted from the sun.

For the same reason solar activity can interfere with radio wave propagation.

intro

antennas

transmitters and receivers