Although not mentioned by name, the "concert given in Medford" would have been broadcast by 1XE, the American Radio and Research (AMRAD) station in Medford Hillside, Massachusetts. AMRAD manufactured radio equipment, so the wireless receiver set "toy" for sale was also made by that company.
Boston Globe, December 21, 1920, page 18:


Telephone  Instruments  on  Sale  at  Filene's

    Taking the mystery out of the wireless telephone and telegraph is the latest achievement of science for the boys of America, who are lured by that hitherto somewhat complicated subject. Not only is the mystery being removed, but today the boy can have instruments for either operation in the den.
    For today, at the Filene store, a wireless receiving set is being exhibited, which is one of the most unusual toys on the market. Through a horn, which magnifies the sounds received, Boston folks listened to a concert given in Medford, to wireless reports from the Brooklyn Navy Yard and to Sundry other commercial messages and small talk of the air.
    The sounds were very clear and audible. The toy is a creation of a company out in Medford, and it has a range of 500 miles, although better conditions prevail with it, at slightly shorter distances. Any boy can carry the receiving set in a satchel. He can link up his wires on his own bed if he chooses, and "listen in" on what the world is saying.