Broadcasting election night returns was a well established tradition by 1920, going back to the earliest days of radio. At first the transmissions were limited to being sent in telegraphic code, until the perfection of audio radio transmitters.
In late October, 1920, Westinghouse rushed to set up a new East Pittsburgh, Pennsylvania station -- which had originally been intended for two-way interplant communication -- in time to broadcast the November 2, 1920 election results. The opening night broadcast used the Special Amateur callsign of 8ZZ. A few days later, the station's broadcast operations switched to using the callsign KDKA, which had been assigned to the Limited Commercial licence issued to authorize the two-way plant communication. (For at least the first year, KDKA appears to have been used for radiotelegraphic communication between factories during workdays, and for broadcasting at night).
Westinghouse's election night broadcast was scarcely noticed at the time -- DeForest's November, 1916 election night broadcast over his New York City station, 2XG, had received much more coverage, and likely had a much bigger audience. But Westinghouse would continue to expand and promote its operations, and quickly became the most energetic promoter of broadcasting activities.
Electrical Review, November 6, 1920, page 733:
SEND ELECTION RETURNS BY WIRELESS TELEPHONE.
An innovation in receiving and transmitting election returns by wireless telephone within a radius of 300 miles of Pittsburgh was inaugurated this year by the Westinghouse Electric & Manufacturing Co. and its subsidiary, the International Radio Telegraph Co. The returns were received direct from an authoritative source and sent broadcast by a wireless telephone stationed at East Pittsburgh, Pa. Receiving stations of almost any size or type were enabled to catch the messages within the radius by means of a crystal detector, a tuning coil, a pair of telephone receivers and a small aerial. By a two-stage amplifier the operator was able to attach his receivers to a phonograph so that messages could be heard anywhere in a medium-size room.