Signals are the means by which we transmit information. Vibration of molecules (sound), smoke signals, and passing electromagnetic waves through circuitry or through the air are all examples of signals. In these introductory notes, we will really only be worried about electrical and electromagnetic means of sending signals.
Electronic communication can occur over wires by passing electric signals through the wires, and we have had the means and the know how to do this for over 200 years. The first wired communication system was the telegraph system set up in 1844 and connected Baltimore and Washington. The image at the top of the page shows Samuel Morse’s penciled letters of the first message (the message seems rather ominous to me). There were also earlier experimental systems that were operational in lab settings in the early 1800s.
Electronic communication can also occur by passing signals through the air on electromagnetic waves. The theoretical basis of wireless communication is based on the work by James Maxwell who developed his famous “Maxwell’s Equations” relating electricity and magnetism. The practical development of a wireless communication system is widely attributed to Guglielmo Marconi who, demonstrated the wireless transmission of morse code over 2 km in 1896, then in 1901 he became the first to receive a signal transmitted over the Atlantic Ocean from Poldhu, Cornwall to St. John’s, Newfoundland.
The rest of this section provides a look at basic properties of signals.
 Although it can be shown that Nikolas Tesla published a paper on wireless communication upon which Marconi likely based his work.