VOICE OF AMERICA
by R.J. Reiman, Historian
In 1941, the war in Europe was escalating and the Axis propaganda machine was in full swing. It was outdoing the Allies' efforts by a factor of at least two in number and in power of the shortwave
broadcast stations as well as hours on the air, languages, etc.
The Roosevelt administration, determined to do something about this, called a meeting of the leaders of companies in the broadcast equipment business, RCA, GE, Westinghouse and, although not a manufacturer, The Crosley Corporation of Cincinnati. It was included because of experience with high power AM transmitters (500 kw) and because of early experience in short wave broadcasting. Crosley, as far back as 1937, broadcast SW first with a "homemade" 10kw "rig", then with a 50kw unit made from an old WLW transmitter. At this time, they had two 50's on the air, WLWO and WLWK.
At this meeting, the government presented a need for six 200kw transmitters to broadcast to Europe, North Africa and South America in a time frame of 2 years or less. The three big companies said they couldn't do it without interfering with the war effort.
Mr. Shouse, President of Crosley, reportedly excused himself from the meeting to call Jim Rock well, his chief engineer. Jim said something like " I think we can, we'll give it a good try,...". On that basis, a one page contract was written and we were on our way in early 1942. A site was selected and design work started.
There were a number of challenges for the relatively small team of engineers at Crosley:
- 200kw power level: This was twice that acheived by any transmitter to date. Development of the tubes for the job would start soon, but prototypes would not be available for two years.
- Unknowns in the capability of insulators and transmission lines at the high RF voltages required.
- High power circuit fault interruption.
- Wartime restrictions and shortages of steel, copper and electronic components.
- Shortages of manpower.
Ingenuity and adaptability were key to the solution of many of the problems.
A real tough problem was the high power RF amplifier where voltages could reach 50KV. How do
you make a variable capacitor to work at 50KV? Using classical flux mapping techniques, a design
was reached with a minimum radius of one inch on the edges of the plates. The cooling water jackets
were designed for the big tubes when they became available but with adapters, smaller 100kw tubes
were used in tests and early operation.
The unknowns in high voltage RF technology were tested in a unique test set-up which used a
one-half wave transformer. Thus insulators, transmission lines, coupling networks, etc. were exposed
to the real world.
Unique 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. Two 45 foot wooden utility poles were connected at the butt ends with a metal sleeve and
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 fault, say an arc in a power tube, by the 750KVA power supply could produce
a melt down. 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.
Building 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. In fact,
much had to happen at the same time to meet the 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 whole station was operational, which was a
truly remarkable feat considering the small engineering staff and the wartime obstacles.
At that time, it was the most powerful Short Wave Station in the world. Those transmitters remained
in operation for 47 years after which they had to be replaced because power tubes were no longer
NOTE: Special thanks to C.C. Bopp for this History of The Voice of America