Herman's call sign 'W-6-XRL4' indicates his geographical region ('W' for USA and '6' for California) and his unique identifier (in this case, a mock code, since the last suffix-character should always be a letter).
Herman sings "My Mother's Eyes" (music by Abel Baer, L., lyric by Wolfe Gilbert), the theme song from the motion picture Lucky Boy (1929).
Grandpa's transistorized divining rod can be programmed to search for Girls, Metal, Water and Flying Objects.
"Ham radio" is an informal name for an amateur radio operator. As early as 1901, the terms "ham" and "plug" were used by landline telegraphers to describe an operator "who lacks ability" or who had poor or "ham fisted" skills.
The ham radio operator who gives Herman a "raspberry" for singing "My Mother's Eyes" is from Milan, Italy.