Propagation

Related wiki pages are Feedlines and Antennae QRN, Tropospheric ducting

Propagation Prediction
Australian Space Weather Agency (IPS)

Propagation Theory (unfinished)
Radio frequencies form a fragment of the entire electromagnetic spectrum. It is generally considered that radio frequencies are found between 10 kHz and 300 GHz. 10 kHz is considered to be the lower end of the electromagnetic spectrum. Above 300 GHz infrared begins.

Electromagnetic energy travels as waves that move at the speed of light (300 000km/s), normally in a straight line. Atmospheric conditions can affect radio transmissions, and are responsible for transmissions between ham radio stations that are not a "straight line" distance apart.

Electromagnetic waves have two components, electric and magnetic. These are at right angles to each other. Unlike sound waves, electromagnetic waves do not need a medium through which to pass. Hence radio transmissions to and from deep space are possible.

Interference
Related wiki pages: Broadband over Power Lines (BPL) What causes QRN?

Interference or noise (also known as QRN) is the effect of unwanted radio signals in the same frequency that one is listening to or wishes to transmit on. Interference is generally classified as being either man-made, terrestrial or cosmic.

Man made interference is created by man-made electrical devices. Broadband over Power Lines (BPL) is a good example of this. Links to another page of this wiki can be found below.

Terrestrial sources include lightning, which is generally worse in summer on the lower HF bands, due to increased numbers of storms. Rain and snow storms can also produce significant interference.

Cosmic interference results from the emission of high energy radio waves from stars including our own sun. The sun has by far the greatest effect in this category, due to its proximity to Earth.