More about Crosley's mysterious WLWO.
- More on Crosley's mysterious WLWO.
By R.J. Reiman:
In 1941 the war in Europe was escalating, and the Axis propaganda stations were outdoing the Allies' efforts in number, both in power and in hours on the air.
The Roosevelt administration called a meeting of broadcast-equipment makers, RCA, GE, Westinghouse ... and the Crosley Corporation of Cincinnati because of its experiences with high-powered transmitters and in short-wave broadcasting. In 1937, Crosley was broadcasting short-wave over WLWO and WLWK with a 50kw unit made from an old WLW transmitter.
At the meeting, the government expressed its wish for six 200kw transmitters to broadcast to Europe, North Africa and South America within two years or less. RCA, General Electric and Westinghouse said they couldn't do it without disrupting their war efforts.
At this point, James D. Shouse, the president of Crosley Broadcasting, reportedly excused himself to call his chief engineer Jim Rockwell, who said something like "I think we can; we'll give it a good try." A one-page contract was written, a site was selected, and design work began.
The relatively small team of engineers at Crosley was challenged by
1) The 200kw power level, twice that achieved by any transmitter to date. Development of the tubes for the rig would start soon, but prototypes would not be available for two years.
2), Unknowns in the capability of insulators and transmission lines at the high RF (radio frequency) voltages required.
3), High power circuit fault interruption.
4), Wartime restrictions and shortages of steel, copper and electronic components. And,
5), Shortages of manpower.
Ingenuity and adaptability were key to the solution of many of the problems. One major problem was within the high power RF amplifier where voltages could reach 50KV and the difficulty of engineering a variable capacitor to work at 50KV. But using classical flux-mapping techniques, a design was reached using a minimum radius of one inch on the edges of the plates. Cooling-water jackets were designed for the big tubes when those would become available but, with adapters, smaller 100kw tubes were used in tests and early operations.
The unknowns in high-voltage RF technology were tested in a unique test set-up which used a one-half wave transformer, which also tested insulators, transmission lines, coupling networks, et al.
Likewise, original designs were developed for matching, tuning and coupling networks. The unique reentrant rhombic antenna designs proven in application at WLWO would be installed in the antenna field behind the transmitter building. Lacking steel for support towers, an ingenious arrangement was devised whereas two 45-foot wooden utility poles were connected at the butt-ends with a metal sleeve and then erected with guy wires to make a 90-foot support - four per antenna.
Primary-circuit-interruption proved to be a challenge. Even with the fastest circuit breakers available, the tremendous amount of energy delivered to a failure, for example an arc in a power tube by the 750KVA power supply, could produce a meltdown. An electronic circuit interrupter, using back-to-back ignitron tubes in each phase which could disconnect in 1/3 to 1/2 cycle, was devised in a joint effort with Westinghouse. Current limiting devices were also used in primary and high voltage DC circuits.
Construction of the station building, power substation and antennas occurred in parallel with the transmitter development. The latter was done in a rented building in downtown Cincinnati. Much had to happen simultaneously to meet the hurried schedule. Final assembly of the transmitters took place on the site.
By the Spring of 1944, the first transmitter was up and running and in a little over two years, the station was fully operational, a truly remarkable feat considering the small engineering staff and the wartime obstacles. At that time, it was the most powerful shortwave station in the world. Those transmitters remained in operation for 47 years after which they had to be replaced, only because power tubes were no longer available.
(Special thanks to C.C. Bopp for this.)