The "Anacostia Naval Station" that broadcast President Harding's congressional address operated under the callsign of NOF -- its transmitting wavelength of 427 meters corresponds to a frequency of about 702 kilohertz.
Commercial America, April, 1923, pages 27, 29:
President Harding delivering speech to Congress

Broadcasting  the  Presidential  Message  to  Congress

How  the  Words  of  President  Harding  Delivered  to  a  Joint  Assembly  of  the  House  of  Representatives  and  the  Senate  were  Broadcasted  to  a  Huge  Invisible  Audience  over  the  United  States

transmitting equipment in the capitol basement WHEN President Warren G. Harding delivered his message to a joint assembly of the House of Representatives and Senate, on December 8, last, for the first time in the history of the sessions of the American Congress the utterances of a President of the United States were heard by an invisible audience by means of the radio telephone. His remarks were heard as distinctly within a radius of approximately 200 miles of the National Capital as they were by members of the Cabinet who occupied front seats in the House of Representatives. The radical departure of broadcasting the deliverance of a President is epochal, and radio telephony demonstrated certain advantages over Morse telegraphy and Bell telephony as a means of communication. The vastness of the area covered within the twinkling of an eye is a peculiar virtue of this vehicle of intelligence.
    The voice of President Harding on the state of the Union, as he specifically addressed the Fourth Session of the Sixty-Seventh Congress, was probably heard by the largest audience in the history of the world. The seating capacity of the House of Representatives was occupied to the point of overflowing, thus constituting his visible hearers. The invisible audience, it would be hazardous to attempt to name its numbers, was comprised of the thousands of owners of radio-telephone receiving outfits who were apprised of the deliverance of the message and those who had the inclination to "listen in." A microphone mounted on a pedestal, located about four feet from the rostrum on which President Harding stood, received the voice vibrations. From this cup-like device, the sound waves were conveyed by a telephone wire to the Naval Air Station, at Anacostia, D. C, approximately four miles away. Here, the United States Navy Department maintains a powerful radio-telephone transmitting outfit, the one in service at Schenectady, N. Y., under the direction of the General Electric Company, alone exceeding its range as a radiotelephone sending station.
    The message of the Chief Executive of the Nation, having been relayed to Anacostia along a telephone line built by the Chesapeake and Potomac Telephone Company, was broadcasted on 427 meters. The daylight effective range of the radio-telephone transmitter at the Anacostia Naval Air Station is approximately 200 miles, compared to a radius of 750 to 1,000 miles at night. The utterances of the President borne on the medium of electro-magnetic waves, transmitted from Anacostia, were received by newspapers and other radio-telephone stations in the east, west, south, and north and re-broadcasted to another invisible audience. The Pittsburgh Post, Chicago News, Indianapolis News, St. Louis Post-Dispatch, Kansas City Star and Denver Post covered the western half of the country as with a blanket. Northward, wireless stations in Philadelphia, Newark, and the American Telegraph and Telephone Company in New York disseminated the words of President Harding. In the south, the Louisville Courier-Journal and Times, and other newspapers maintaining wireless receiving and sending apparatus, "picked up" the message on 427 meters from the Naval Air Station and re-broadcasted it to thousands of radio-telephone receiving sets in resonance with the transmitters.
    The dignified Secretary of State, Charles E. Hughes, who occupied a front seat in the House of Representatives, was in common with the rural dweller in the isolated farmstead of the boy in the "red schoolhouse" on the hill, in hearing the voice of the Chief Executive of the Nation if the latter perchanced to own a wireless receiving outfit. Fortunately, Mrs. Harding was not denied the privilege of hearing the voice of her distinguished husband on this occasion, since a radio-telephone receiving apparatus was available in the White House, where she has been convalescing from a serious illness for several months. Until her illness the "First Lady of the Land" had accompanied President Harding to the Capitol on every occasion that he addressed a joint sitting of Congress. Liable to attend this time, the "wonderful wireless waves," in part at least, counteracted the disappointment of forced detention in the White House.
    The mechanism for relaying the voice of the President to Anacostia was installed by the Western Electric Company and the local telephone company projected a telephone wire from the Capitol to this point. To the microphone was attached three telephone circuits, with direct connections to the Anacostia Naval Air Station. Only one of these electric circuits was employed in conveying the message of the President. The second circuit was used as a so-called "order wire," thus affording means for telephone engineers to conduct conversations while observing the action of the voice of the President as it was relayed for a distance of about four miles. This observance contemplated the maintenance of an evenness of tone as the voice was impinged on the microphone, and then conveyed by wire to Anacostia. The third electric circuit in the series was an emergency unit, which would have avoided a complete disruption of the service in the event of a breakdown of the other two telephone lines. The system, for the most part, duplicated that in operation when the addresses of the speakers at the dedication exercises of the Lincoln Memorial were relayed to Anacostia and Arlington, from which points they were broadcasted by radio telephone. Also a similar service was maintained at the ceremonies incident to the burial of the "Unknown Soldier" in Arlington Cemetery.
    The radio-telephone installation made in the House of Representatives for the dissemination of the message of President Harding is of a permanent character. This fact, however, does not give assurance that the proceedings of Congress will be broadcasted by radio telephony or wireless telegraphy. The "doings of Congress" may eventually be radiated throughout the United States, but such action is not a certainty at this time. Such a service contemplates the use of a high-power radio-telephone transmitting station, the operation of which, of course, involves the expenditure of money. The wireless telephone and telegraph transmitting stations of the United States Navy Department are dedicated to other services, the dispatch of naval business and the broadcasting of serviceable communications from allied government departments. On this occasion permit to use the radio-telephone transmitter at the Anacostia Naval Air Station was granted by Commander S. C. Hooper, head of the Radio Division, U. S. Navy Department.--Reprinted by permission from Radio News.