The two stations used for this test were operated by the U.S. Navy: NAA, across the Potomac River from Washington, D. C. in Arlington, Virginia, transmitting on the longwave wavelength of 2,650 meters (113 kilohertz), and NOF, located the Anacostia section of Washington, D.C., operating on 412 meters (728 kilohertz on the AM (mediumwave) band).
Radio World, June 3, 1922, page 7:

Code  Messages  Now  Circle  Globe

By  Carl  Hawes  Butman
WASHINGTON. -- "Within a few months, probably, it will be possible for a representative of the U. S. Government to talk to anyone in the world, or to all people at one time, on the new Naval radiophone transmitting set at NAA, the Arlington Station on the Potomac River." This remark was made by a high-ranking officer of the Navy Department, recently, who added that the Navy could now send code messages practically around the world, by the use of relays.
    Speaking into any ordinary telephone in Washington connected with the Arlington Broadcasting Station, an official could talk to a Pacific Coast station, which would automatically relay the message within a sixtieth of a second to Pearl Harbor, thence to Guam and Cavite, where the message would arrive in one quarter of a second after it left Washington. The further routing he did not explain, but is is known that other big stations are in prospect overseas.
    The simultaneous broadcasting of a single spoken message from two stations on different wave-lengths was successfully conducted for the first time by the Navy on Saturday, May 20, for the purpose of making sure that plans for broadcasting the headquarters dedication program of the National Woman's Party were satisfactory. Through the cooperation of the American Telephone and Telegraph Company, direct wires were strung from the Woman's Party Headquarters to the Naval Air Station at Anacostia, D. C., and the Naval Radio Station at Arlington, Va. Test messages spoken at the headquarters were transmitted by wire to these stations and put on the radio-broadcasting circuits. At Anacostia, NOF, a 412-meter wave was used, with about 13 amperes radiation; at Arlington, NAA, on a 2,650 meter wave, with 40 amperes.
    The system worked perfectly, serving two classes of receiving stations at once, the 412-meter wave furnishing many amateur stations within from 400 to 700 miles, while the long wave served stations equipped with larger receiving sets, between 800 and 1,500 miles distant.
    The actual broadcasting of the speeches, Sunday afternoon, however, was prohibited by Naval officials Saturday, on the ground that the meeting was of a political nature such as was previously ruled against by Edwin Denby, Secretary of the Navy.
    The experiments in simultaneous broadcasting from two stations on different wave-lengths have been so successful that, it is believed, several stations, not too greatly separated, will soon be able to broadcast a single phone message on a number of different wave-lengths at one time, reaching receiving stations nearby and at great distances, even crossing oceans to powerful foreign stations.
    With the perfection of this system and the necessary apparatus, President Harding, for example, could address practically the whole world, or at least all the people provided with suitable receiving apparatus who understand English. This would furnish an excellent method of issuing official verbal statements of serious import or bearing on the policies of the country. The broadcasting of a direct personal message, such as President Wilson made to Congress on the day the United States declared war, would have made America's position immediately known to the world. It is unlikely that any international broadcasts will be sent out by the Naval stations except experimentally or in the event of a declaration of vital national importance. The station is for official use only.