Interference with consumer electronics, grounding, DSP

At some point or another, your amateur radio station will interfere with a radio or television set, a PA system, or a telephone. A SSB transmission generally causes some kind of humming, while a CW transmission can cause humming or clicking. Sometimes this may be your fault, other times it may be the fault of the device. In either case, you should do everything you can to eliminate this interference.

Sunspots and solar radiation, ionospheric disturbances, propagation forecasting, and indices

Amateur radio communications are subject to the whims of nature. Many different phenomena affect the propagation of signals, and it behooves you to know a little something about the phenomena. Doing so will make you a more effective amateur radio communicator.