generate questions: Returning home to Brantford after six months abroad, Bell continued his experiments with his "harmonic telegraph".[N 12] The basic concept behind his device was that messages could be sent through a single wire if each message was transmitted at a different pitch, but work on both the transmitter and receiver was needed.
How many wires did Bell send a signal through? {sep_token} For  his system to work, Bell had to change what about each code? {sep_token} Bell needed to fix both the transmitter and what? {sep_token} Where was Bell's home? {sep_token}