Etymology of ham radio
Ham is an informal term for an amateur radio operator, and, by extension, "ham radio" refers to amateur radio in general. This use of the word first appeared in the United States during the opening decade of the twentieth century — for example, Robert A. Morton in "Wireless Interference", from the April, 1909 Electrician and Mechanic, reported overhearing an amateur radio transmission which included the comment: "Say, do you know the fellow who is putting up a new station out your way? I think he is a ham." However, the term did not gain widespread usage in the United States until around 1920, after which it slowly spread to other English-speaking countries.
One reason for the slow adoption was related to the word's origin, as one of many insults employed by landline telegraph operators at the time, for it originally meant a "poor operator"., ("Ham" was also already in more general use as a slang word meaning "incompetent", most commonly in the phrase "ham actor".) Early radio (initially known as wireless telegraphy) included many former wire telegraph operators, and within the new service "ham" was employed as a pejorative term by professional radiotelegraph operators to suggest that amateur enthusiasts were unskilled — in "Floods and Wireless" by Hanby Carver, from the August, 1915 Technical World Magazine, the author noted "Then someone thought of the 'hams'. This is the name that the commercial wireless service has given to amateur operators..." A letter from a Western Union Telegraph Company employee, printed in the December, 1919 edition of the amateur radio publication QST, showed familiarity with the word's negative connotations, expressing concern that "Many unknowing land wire telegraphers, hearing the word 'amateur' applied to men connected with wireless, regard him as a 'ham' or 'lid'". However, during this period many other amateurs were in the process of proudly adopting "ham" as a description of their hobby, embracing the word that was originally an insult, similar to the way Yankee Doodle evolved. (See, for example, Thomas F. Hunter's exuberant "I am the wandering Ham" from the January, 1920 QST).
In spite of — or perhaps because of — its relatively straight-forward origin, many interesting and colorful folk etymologies about the supposed origin of "ham" have been developed over the years. Below are some of the competing later explanations that are often charming, but also wrong.
One alternate explanation is that "ham" is a shortened version of "ham-fisted", meaning clumsy. This is a reasonable conjecture, given that all early amateur radio stations used hand-operated telegraph keys to transmit Morse code, and sending style is referred to as an operator's "fist", so someone who sends badly could be called ham-fisted. But the earliest references to "ham" use only the single word, and there is no evidence that it evolved as a truncation of a longer phrase.
"A little station called HAM"
This widely circulated but fanciful tale claims that, circa 1911, an impassioned speech made by Harvard University student Albert Hyman to the United States Congress, in support of amateur radio operators, turned the tide and helped defeat a bill that would have ended amateur radio activity entirely, by assigning the entire radio spectrum over to the military. An amateur station that Hyman supposedly shared with two others (Bob Almy and Peggie Murray), which was said to be using the self-assigned call sign "HAM" (short for Hyman-Almy-Murray), thus came to represent all of amateur radio. However, this story apparently first surfaced in 1948, and virtually none of the "facts" in the account actually check out, including whether "a little station called HAM" ever really existed., , 
"Home Amateur Mechanic" magazine
In this version, supposedly HAM was derived from the initials of a "very popular" magazine which covered radio extensively. But there is no evidence that there ever was a magazine by this name.
It is sometimes claimed that HAM came from the first letter from the last names of three radio pioneers: Heinrich Rudolf Hertz, Edwin Armstrong, and Guglielmo Marconi. However, this cannot be the source of the term as Armstrong was an unknown college student when the term first appeared.
Likely an example of corporate wishful thinking, Hammarlund products were supposedly so pre-eminent in the pioneering era of radio that they became a part of the language of radio. As the story goes, early radio enthusiasts affectionately referred to Hammarlund products as "Ham" products, and called themselves "Ham" operators. In truth, Hammarlund was a minor and barely known company at the time "ham" started to be used.