Final answer:
Edwin Armstrong invented a circuit for nationwide broadcasting in 1934, introducing the frequency modulation (FM) system as an improvement over the existing amplitude modulation (AM) system.
Step-by-step explanation:
Edwin Armstrong invented a circuit that allowed for nationwide broadcasting in 1934. He developed the frequency modulation (FM) system, which greatly improved the quality and range of radio broadcasts compared to the existing amplitude modulation (AM) system. FM radio became popular in the 1940s and eventually became the standard for radio broadcasting.