Radio Theory 3

$Radio Theory Ground Waves (Surface Mode) These are radio waves that follow along the surface of the earth, they are able to diffract or bend around obstacles and this causes them to follow the curvature of the earth. Surface attenuation or "clinging" is one way in which these waves follow the curvature of the earth. Part of the wave comes into contact with the surface of the earth and "clings" to it and slows down causing a downward tilt in the wave. Sky Waves (Ionospheric Mode) These are radio waves that are sent up towards space and then reflected back to the earth from the ionosphere. This reflection allows the sky waves to travel a very long distance often far beyond where the ground waves stop. The area between where the ground waves end and the sky wave touches back down at the earths surface is called the skip zone; within the skip zone the signal will be erratic or non-existent. Sky waves will travel further at night than during the day. They can also be affected by solar activity and other electromagnetic disturbances. LF / MF and HF can utilize both ground and sky waves for propagation while VHF and UHF typically penetrate the ionosphere and speed out into space they are known as "Line-of-Sight" waves.$

Line of Sight (Direct Mode) VHF waves don't bounce or bend along the ground like LF / MF and HF waves, For this reason they are Line of Sight and will need to travel directly from one antenna to another, they are relatively free of atmospheric and precipitation static. Single Side Band (SSB) Single sideband (SSB) is a type of HF radio transmission in which only one of the sidebands of the signal is allowed to be transmitted and the other sideband and the carrier are suppressed. Once the signal gets to the receiver the carrier can then be re-inserted, in a normal AM signal we have three components: the carrier two sidebands called the upper sideband and the lower sideband