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"Wavescan" is a weekly program for long distance radio hobbyists produced by Dr. Adrian M. Peterson, Coordinator of International Relations for Adventist World Radio. AWR carries the program over many of its stations (including shortwave). Adrian Peterson is a highly regarded DXer and radio historian, and often includes features on radio history in his program. We are reproducing those features below, with Dr. Peterson's permission and assistance.
Wavescan N622, January 24, 2021
KDKA Mediumwave and Shortwave in Pittsburgh: Unusual Radio Events
As is so well known, mediumwave radio station KDKA in Pittsburgh, Pennsylvania was not only a pioneer broadcasting station, but it was also a station whose equipment was in use for progressive radio experiments. A very interesting three page article about the history of station KDKA was published in the November 24, 1941 edition of the American trade journal "Broadcasting."
This now historic article was prepared by Dwight A. Myer, who was the Chief Engineer at KDKA back then, and it was written to commemorate the station's 21st anniversary. In his extensive information, Myer mentions several different facts about radio station KDKA that are not usually included in historic information about this station.
As has been presented here in Wavescan on previous occasions, the inaugural broadcast from station KDKA began at 6:00 pm on Tuesday evening, November 2, 1920, under the temporary callsign 8ZZ. A new 100 watt transmitter was specially constructed for the occasion, and its operating channel was 550 metres (545 kHz), at the bottom end of what subsequently became the standard mediumwave band. The entire 8ZZ-KDKA radio station was installed in a temporary wooden hut on the top of the flat-roofed Building K at the Westinghouse factory in East Pittsburgh.
However, it is not generally known that test transmissions were made in advance at that same factory location with the use of another radio transmitter in order to test the feasibility of the intended project. The temporary test transmitter was Engineer Frank Conrad's own amateur station 8XK that was brought in specially for the occasion from his home in nearby Wilkinsburg. The 8XK transmitter was described as a breadboard layout using two 50 watt tubes, and the antenna system was a six wire flat top that was afterwards used for the inaugural broadcast.
When the station was subsequently on the air for its regular daily programming, the operators needed to know that the station was actually on the air. For this purpose they needed a monitor receiver, so therefore they rigged up a small portable crystal set receiver with headphones. The on-duty operator carried this primitive monitor radio receiver with him constantly.
However, there were occasions when carrying a portable crystal receiver was inconvenient, so instead, they rigged up another type of radio receiver to monitor the transmissions from the KDKA radio transmitter. An original Fleming valve or tube was placed close to the transmitter, and enough RF energy was thus picked up to activate a large headphone which was attached to the narrow end of a motor car horn. This combination served as a radio receiver with a loud speaker.
The second location as the transmitter site for KDKA was on top of a low hill on Greensburg Pike, Forest Hills, which was taken into service on August 13, 1924. Three years later, a new full power 50 kW mediumwave transmitter was inaugurated at this location, and the radiation system was a diamond shaped rhombic antenna. However, each leg of the diamond was in itself a multi-wire cage antenna.
Now, when the new KDKA transmitter station was taken into service at this new location in 1924, what happened to the one year old 1 kW transmitter that was previously in use on the top of Building K in East Pittsburgh? Well, that transmitter was dismantled and shipped to Chicago, where it was incorporated into the technical equipment of the Westinghouse three year old KYW, Chicago's first radio broadcasting station.
In 1927, Westinghouse radio KDKA installed an experimental ultra shortwave transmitter at Forest Hills that was capable of emitting RF signals on 10 meters (30,000 kHz). That was indeed a pioneer event back then. These days the radio spectrum around 30 MHz is in use for amateur and commercial communications.
Then a year later (1928), at the same Forest Hills location, a shortwave transmitter was designed so that it would emit both amplitude- and frequency-modulated signals simultaneously. In this unusual arrangement, this special transmitter could emit both AM and FM signals on 63 metres at the same time.
When the Allison Park transmitter station was planned in the era immediately before the commencement of World War II, it was intended that the KDKA shortwave service via WPIT would also again be co-sited with the mediumwave. However that did not happen. Instead, station WPIT was transferred from Pittsburgh to Boston; and that's a story for another time.