Re: Fading
In general there are two sources. The first is attenuation through the path. This is more important at HF sky wave signals and does not occur noticeable on VHF local signals.
Multipath is the source of most fading. This is where the signal arrives over two or more paths and they have different lengths which produce different phases at the receiver antenna. On HF sky wave this is usually two paths. On VHF local it can be many.
The different statistics of the resulting amplitude is based on the number of paths and their signal strengths relative to each other.