Popular Mechanics, January, 1920, page 117:
OPERA BY RADIO IS NOVELTY OF ELECTRIC EXPOSITION
A wireless-telephone receiver in the Signal Corps booth from which issued the strains of familiar grand-opera selections, was a striking novelty of Chicago's recent electrical show. The music was transmitted from a station about a mile distant, a phonograph supplying the airs. That the clearness and strength of the transmission were not dependent on the short range, became evident when the radio operators at Ludington, Mich., and Milwaukee, Wis., sent thanks for the entertainment thus furnished them.