Science and Invention, March 1922, page 1043:

Radiophoning  To  and  From  "L" Trains
outside photo IF the present plans of the Chicago Elevated Railroad do not miscarry, the patient straphangers will gladly pay the present fare of 8 cents without any murmur, and be willing to donate an extra dime or two for the privilege of riding on the elevated. The elevated system is figuring on installing a radio system on its cars and furnishing its passengers with songs, music, and even grand opera, on their way to and from work. Pretty soon it will be a privilege to work; not only will the passenger be entertained, but it will be possible for you to call your home while in transit and suggest what kind of meat you want for dinner.
    The first trial of the radio was made on a Chicago, North Shore & Milwaukee electric line recently. A dozen pretty girls from the offices of the line danced with the road officials to the strains of music transmitted from the radio station on top of the City Hall. They were also able to carry on conversation, i. e., talk to as well as hear, the chief of the fire alarm system in Chicago, and every test proved eminently successful.
    One of the accompanying photos shows the girls, on the Chicago elevated train enjoying a dance to the music being sent from the radio transmitting station in Chicago. Another photograph shows a passenger talking from the moving train to his home in the city via radiophone, while the third photo shows how the antenna wires are mounted on insulators along either side of the roofs of the "L" train.
    The radiophone transmitting set used in this test was equipt with vacuum tubes for producing the necessary high frequency oscillatory current suitable for charging the antenna, together with a high voltage d. c. dynamo, the current from which is acted upon by the vacuum tubes in the production, as well as the voice modulation of the high frequency oscillations.
inside photos