One popular theory is that it is the conbination of the initialsof the last names of three 
Harvard students who supposedly had an amateur station in the teens.Their names were 
supposedly Hyman, Almay, and Murray, and they operated the little stationwith a call sign 
of HAM. . The problem with this theory is that an exhaustive searchof theCongressional 
Record turns up no such speech, and Harvard has no record of littlestation HAM. 

     Another theory holds that it derives from whatcommercial operators called amateurs. 
They referred to them using the old telegrapher's insult of "ham fisted",meaning that they 
weren't of professional skill. This may be the true origin of the term,but it seems unlikely 
that amateurs would willingly adopt a term meant to be insulting tothem as their name. 

     A third theory derives from the fact that HugoGernsback published a magazine called 
Home Amateur Mechanic in the early days of radio and it included manyradio construction 
projects. Thus when asked what sort of radio a person had, he mightsend back that he 
had one of those HAM radios (using just the initials of the magazinename in true CW 
shorthand fashion). I like this explanation best.