In 1904, Abraham White, president of the American De Forest Wireless Telegraph Company, saw the Saint Louis Exposition as the perfect opportunity for promoting his company as the preeminent radio firm in the United States, and also, not coincidentally, a chance to sell a lot of stock of dubious value. (According to Susan J. Douglas' 1987 book, Inventing American Broadcasting, Guglielmo Marconi had also planned to set up a display at the fair, but withdrew when he learned that De Forest was going to be there).

White lived up to his reputation as a skilled promoter by staging an impressive collection of displays, along with exaggerated accounts of his company's accomplishments. The article below appears to have accepted many of these claims at face-value--in particular, the reports of stations transmitting simultaneously without interfering with each other were really more a hope for the future than what the De Forest equipment was actually capable of at this time. Still, as a promotion White's efforts were a success, as De Forest Wireless, followed in 1906 by its successor, United Wireless, would become the largest U.S. radio corporation, until its collapse and bankruptcy in 1912, when it was taken over by Marconi.

The Electrical Age, September, 1904, pages 161-167:

operator at work

Wireless  Telegraphy  at  the  St.  Louis  Exposition
tower EACH great World's Exposition has been characterized by the presentation of some prominent invention. At the Centennial Exposition the telephone was first presented as a scientific curiosity; Chicago saw the incandescent lamp applied for the first time on an adequate scale for general and ornamental illumination; and the St. Louis Exposition may be similarly characterized as the first to present in an adequate and comprehensive way the new art of wireless telegraphy.
    This latest invention is well shown in the exhibit of the De Forest Wireless Telegraph Company, who have on the fair grounds ten operative sets of instruments representing seven separate stations. The De Forest observation tower stands prominently at the entrance to Orleans Plaza, 300 feet in height, and is equipped with two electric elevators. These are in constant operation, and the many visitors to the top of the tower evidence the popular interest in this new art of wireless telegraphy, as well as an appreciation of the opportunity for obtaining a bird's-eye view of the main picture of the fair.
    The wireless telegraph station on this tower is on the 100-foot platform, far above the building tops and over-looking Forest Park. The walls of the station are made entirely of glass, and in the distance may be seen the masts of the two downtown newspaper stations, to which the wireless messages are being continually sent. The St. Louis "Post Dispatch" and the St. Louis "Star" receive regular daily news service from this station. From 3000 to 5000 words per day are transmitted at a rate of 25 to 35 words per minute, detailing such World's Fair news as the reporters of the two papers can collect upon the fair grounds. The downtown operators are located in the press or setting-up rooms of the newspapers and hand the copy directly over to the typesetter. station interior
    On this observation tower the antennæ lead tip to a gaff extending from the roof of the tower, a distance of 200 feet. Notwithstanding the fact that the steel structure of this tower does not make it well suited for wireless telegraph transmission, messages have been received from this station as far away as Springfield, Ill.,--a distance of 105 miles. Were this tower of wood, a considerably greater distance could be attained. The wireless tower is covered with incandescent lamps, over 3500 being used in its decoration, and at night it stands out conspicuously, far above all the other buildings, even overtopping the crown of Festival Hall.
    The power supplied at the observation tower is direct current at 500 volts. A 70-H. P. motor-generator transforms this voltage to 240, at which pressure the current is supplied to the elevator motors. On the 100-foot platform a 240-volt motor drives by belt a 2-K. W., 60-cycle, 110-volt generator. This latter voltage is used for the wireless telegraph transmitter. The ordinary Morse key of the transmitter breaks up the 60-cycle current into the dots and dashes of the telegraph code so rapidly that a speed of transmission is attained fully equal to any on land wire.
    Next in importance are the three De Forest exhibits in the Government Building. Of the seven patents chosen by the United States Patent Office to be represented at the World's Fair, those relating to wireless telegraphy probably command the most popular interest. In the same building the United States Signal Corps has two De Forest sets in operation, and messages may be received from either the observation tower or the Patent Office station. In the Government Building the power is taken from a 25-cycle current, and as the De Forest coil is of open-cord type it will not operate satisfactorily on this low frequency. A Wagner motor-generator of 1-K. W. capacity is therefore used to transform the current from 25 to 60 cycles, 110 being the voltage in each case. wireless auto #3
    Visitors to the Electricity Building have their attention drawn to the southwest corner by the sharp and penetrating crackle of the high-frequency, wireless-telegraph spark in the De Forest booth. Here stand the tallest structures in the building, three slender towers of wood, reaching up 75 feet to the eaves of the building, representing, in facsimile, the 225-foot towers which the American De Forest Company are about to erect at Cape Flattery, Wash., for Alaskan and trans-Pacific service. From the tops of these three towers depend three screens of fine antennæ, converging at the bottom to the bright helix on top of the transmitting instrument.
    All day long the operators at this booth are busy transmitting and receiving messages from the tower of the long-distance station or from the Fort Wayne station in the same building. A very popular test by the public is to write out messages at the station in the Fort Wayne exhibit and, strolling over to the main De Forest booth, find them already written out by the operator there.
    Some very interesting work in tuning or syntonic wireless telegraphy, showing the ability of the De Forest system to operate several different transmitters simultaneously without interference, is shown there every day. The receiving operator can, at will, attune his receiver to the messages from the Fort Wayne station, from the observation tower, or from the long-distance station on Art Hill.
    In the Electricity Building the 60-cycle current is obtained directly from Machinery Hall. There the 2-K. W. transformer, which is regularly rated for 300-mile transmission over water and 100 miles over land, is exactly similar to that in the observation tower.
    But perhaps the most interesting of all the De Forest installations upon the Exposition grounds, especially to the electrician and technical man, is the long-distance station on Art Hill. The tall mast of latticed wood, holding aloft its gigantic cross-arms, 210 feet above the hill, towers far above the white walls of "Old Jerusalem" with its star and crescent.
    The ground plate at the long-distance station consists of 140 square feet of copper plate, buried 8 feet directly below the station. Means are provided for maintaining this in a damp condition.
    At the Electricity Building, the ground is made to the system of water pipes and, at the wireless observation tower, directly to the frame of the tower itself. This latter arrangement makes the wave length of the antennæ considerably longer than if they were suspended from a wooden structure and the ground were made in the ordinary manner. towertower
    The arrangement of antennæ at the long-distance station is interesting. Along the 40-foot cross-arm hangs a horizontal wire from which 20 verticals are suspended. These antennæ average 250 feet in length and are bowed out from the mast to a great distance by means of cord spreaders. The antennæ enter the roof of the building in two sections of 10 wires each. The receiving antennæ are entirely distinct from these. Within the building, which is 20 by 40 feet, the visitor sees only the operating table, the relay keys and the receiving instrument. The large transformer, condensers and other apparatus are placed in a separate room; through a window in the partition, however, one may see the dazzling brilliancy of the enormous spark which accompanies every signal. This spark has been so successfully muffled as to be scarcely audible outside of the building, but when the doors of the muffler are opened, a roar is heard, reminding one of the cannonading at the Boer war show, nearby.
    Messages have already been sent from this station to Springfield, Ill., where the signals are heard in the telephone with a sound, as described by one operator, "like the rattling of stones in a tin pail." Overland service with Chicago and Kansas City awaits only the completion of similar masts at those two cities.
    Although the station in the Electricity Building is only a quarter of a mile away from this long-distance station, the operator there, with his receiver connected to the 75-foot antennæ, is entirely unaware of the transmission of messages from this large power station, until he has attuned his instrument carefully to the wave-length of that transmitter. Similarly, at the "Post Dispatch" and the "Star" stations downtown, the operators are receiving press dispatches continually from the observation tower while the long-distance station is transmitting to Springfield. On several occasions two operators, each with a distinct receiving and tuning apparatus, were connected to the same receiving wire downtown, and while one received dispatches from the long-distance station the other operator read messages from the observation tower.
    In addition to the foregoing stations, the De Forest Company exhibit in the Transportation and Electricity Buildings their wireless telegraph automobiles, such as they used so successfully in sending stock quotations from the New York curb exchange to the brokers' offices nearby.
art hill station