The reason why an amateur radio operator is called a 'HAM' is not known. Some relate these three letters (HAM) to the names of three great radio experimenters.

They are-

• Hertz (who practically demonstrated the existence of electromagnetic waves in 1888),
• Armstrong (who developed a resonant oscillator circuit for radio frequency work) and
• Marconi (the 1909 Nobel laureate in Physics, who in the year 1901 established the first transatlantic radio contact).
  

Some people believe that when the young and inexperienced radio enthusiasts began to venture on air with crude spark transmitters based on vehicle ignition coils, their Morse code transmission must have been pretty poor and professionals dismissed them as 'ham fisted'!

While others have their own version; according to them during the earlier days of radio communication, government stepped in to conquer short-waves and allowed the radio amateurs to operate only on certain frequencies; thus the frequencies of amateur radio stations were sandwiched like a 'ham sandwich' and so amateur radio operator came to be called a 'HAM'.         

Another speculation is that  the word "HAM" stands for " Help All Mankind" as reflected in its service towards people in distress during natural calamities, disasters and civil emergencies!

"Ham: a poor operator. A 'plug'."

That's the definition of the word given in G. M. Dodge's The Telegraph Instructor even before radio. The definition has never changed in wire telegraphy. The first wireless operators were landline telegraphers who left their offices to go to sea or to man the coastal stations. They brought with them their language and much of the tradition of their older profession. In those early days, spark was king and every station occupied the same wavelength--or, more accurately perhaps, every station occupied the whole spectrum with its broad spark signal. Government stations, ships, coastal stations and the increasingly numerous amateur operators all competed for time and signal supremacy in each other's receivers. Many of the amateur stations were very powerful. Two amateurs, working across town, could effectively jam all the other operators in the area. When this happened, frustrated commercial operators would call the ship whose weaker signals had been blotted out by the amateurs and say "SRI OM THOSE #&$!@ HAMS ARE JAMMING YOU."Amateurs, possibly unfamiliar with the real meaning of the term, picked it up and applied it to themselves in true "Yankee Doodle" fashion and wore it with pride. As the years advanced, the original meaning has completely disappeared.

There is a continuing debate on what the activities carried out by radio amateurs should be called. Some radio amateurs complain that the terms 'ham radio' is derogatory, and some even object to being called 'amateurs' on the ground that this may be taken to imply 'amateurish', but in fact nowadays amateur radio communication system is of more than the professional standard. Today, with most traffic sent by machine telegraphy or data communication, it is observed that there are fewer professional stations availing these facilities and Morse code heard on the amateur radio bands is of more than the professional standard.