One of the most heralded radio advances during World War One was the development of compact and rugged vacuum-tube transmitters, which allowed airplane pilots to communicate with persons on the ground. During the war, the Glenn L. Martin Aviation Company of Cleveland, Ohio was one of the companies which produced radio transmitters for military aviation.
At the time of the broadcast reported in this article, the ban on commercial and civilian operation of radio transmitters was still in effect, so the Martin company presumably operated its station under a wartime military authorization. (The ban on civilian radio listening had ended just two days before this broadcast took place.) Although this article reported that a series of weekly radio concerts were planned, it is not clear how many additional broadcasts were ever actually made. However, the April, 1920 issue of QST noted that two Glenn L. Martin stations in Cleveland, still using their "air station" calls of UM and GMC, were on the air with radiophone transmssions. (A letter in the July, 1920 issue of this magazine listed the callsign of the Glenn Martin Aircraft station as GMA)
Electrical Experimenter, August, 1919, page 351:
CARUSO CONCERTS TO AMATEURS BY WIRELESS 'PHONE.
Cleveland, Ohio, or that portion equipt with wireless receiving instruments, heard its first wireless telephone concert on the night of April 17th. And it is to become a permanent institution.
Every Thursday night between 8 and 10 o'clock the radio amateur or professional who "tunes" his instrument to receive wave lengths of 375 meters will be able to listen to strains from Caruso and Sousa's band interspersed with baseball scores and the latest news bulletins.
The concert will come from the plant of the Martin Company, air plant manufacturers and will be audible to wireless operators within 200 miles. It is estimated that 400 radio amateurs "listened in" on the first concert.
The wireless transmission of music is accomplished by use of the wireless telephones as developt by F. S. McCullough, wireless expert for the Martin Company. The same apparatus as is used in airplanes is employed and the music produced by a phonograph. The transmitting apparatus of the telephone replaces the phonograph horn. The baseball news and bulletins were announced by voice, so that no knowledge of "codes" were required to receive them.
The Glenn L. Martin Company participated in at least one other pioneer broadcasting experiment. In 1945, it and Westinghouse were reported to be developing "stratovision", which involved TV and FM broadcasting using transmitters that were placed on circling B29 aircraft.