Despite the assertion by this article that this was the first broadcast from "the halls of Congress", at least two earlier broadcasts from that location had already occurred: President Harding's message to Congress on December 8, 1922, plus House debates that were broadcast on December 22, 1922.
WCAP was deleted in 1926 when AT&T sold its broadcasting assets to the Radio Corporation of America, but the other five participating stations are still on the air, although all have changed callsigns: WEAF is now WFAN, WJAR is WHJJ, WDAF is KCSP, KSD is KTRS, and WFAA is KLIF.
Washington Post, December 4, 1923, page 9:
PRESIDENT'S SPEECH WILL BE BROADCAST
It is announced by the American Telephone and Telegraph Company that arrangements have been completed to broadcast the President's address to Congress. Microphones have been installed in the House of Representatives and special circuits have been set up for the purpose. Calvin Coolidge, President of the United States, will read his message to Congress in person, and it will be made available to a vast radio audience through six high-power broadcasting stations.
These are WEAF, American Telephone and Telegraph Company, New York city; WCAP, Chesapeake and Potomac Telephone Company; Washington. D. C.; WJAR, Outlet Company, Providence, R. I.; WDAF, Kansas City Star, Kansas City, Mo.; KSD, St. Louis Post Dispatch, St. Louis, Mo., and WFAA, Dallas News, Dallas, Tex.
This is the first occasion upon which microphones for use in connection with radio broadcasting have been installed in the halls of Congress and it is also the first occasion that the voice of Calvin Coolidge will be picked up by microphones for immediate broadcasting.
Within range of these stations are hundreds of thousands of receiving sets and it is considered quite likely that more than a million and a half persons will listen in on this occasion.
It is also announced that on December 10, President Coolidge will make a special address before microphones installed at the White House in behalf of the Harding Memorial association at 6:30 p. m. This will be broadcast by station WCAP, Washington.