In the late 1930s, Shepard had become interested in Frequency Modulation (later known as FM). In 1937 a plan was developed envisioning that 90% of New England could be provided with FM programs by building mountaintop stations, consisting of a 50 kilowatt transmitter on Mount Asnebumskit at Paxton, Massachusetts, plus 5 kilowatt stations on Mount Washington in New Hampshire and Mount Mansfield in Vermont. (Later plans dropped the proposed Mount Mansfield station). With the help of the inventor of FM, Major Edwin H. Armstrong, the Yankee Network inaugurated the nation's first FM radio network, beginning with an early January 1940 demonstration of an FM inter-city relay, linking Shepard's experimental FM station W1XOJ in Paxton, Massachusetts, to an FM transmitter at station W1XPW in Meriden, Connecticut (now WHCN), to Armstrong's W2XMN in Alpine, New Jersey, to the parent broadcasting system based in the studios of WEAF in New York. Shepard's FM network officially made its debut in December 1940 when W1XOJ in Paxton was permanently linked with W1XER on Mount Washington. Because of their superior audio quality, the FM stations became known for broadcasting live classical music concerts.