IAN LANG ELECTRONICS
Marconi was responsible between 1901 and 1907 for the establishment of wireless telegraphy across the Atlantic Ocean. His telegraph sent Morse Code and was in essence a binary system, amplitude high and amplitude low. It was most useful for ship-to-ship and ship to shore signals.
On April 14-15 1912 the Marconi operators on the Titanic, Jack Phillips and Harold Bride, sent a telegraphic CQD (distress call) which was picked up by David Sarnoff, another Marconi man at that time, who stayed in touch with the Carpathia over the next 72 hours whilst survivors were rescued. Were it not for Marconi's wireless telegraph system, many more lives would undoubtedly have been lost that night.
Amplitude modulation was the first method used in radio communications and is still an important technology today. Important pioneers were William Preece Guglielmo Marconi, and Reginald A Fessenden, the latter two having short articles about them on this site.
In this section we will look at the general theory of continuous sine waves, relate that to AM, and discuss a few important practical considerations to be borne in mind.
General Theoretical Concerns in AM
All radio communications are made using an electro-magnetic wave that is sinusoidal in nature. Let us consider the general form for the instantaneous value of electrical waves:
The graphical representation is as below:
From this we can see that if we alter anything on the right hand side of the equation, we also alter v on the left.
fig1:unmodulated carrier wave