Although a half-hour segment of the Grand Ole Opry reached the nation each Saturday night over the NBC radio network, the program left its deep impression on our culture because millions of Americans from Maine to Florida to Colorado could pick up the entire program over WSM directly. Not only did WSM’s signal occupy a ”clear channel,“ with an exclusive nationwide claim on its place at 650 on the AM dial, it was also cranked up to 50,000 watts of power and transmitted into the air through a million pounds of radiating steel.
The WSM tower is that slender, diamond-shaped antenna standing just to the left of I-65 as one nears Franklin. Originally 878 feet high, it was the tallest radio tower in the United States when it was built in 1932. Only four towers of similar design and vintage were constructed; of those, only WSM’s and WLW’s in Cincinnati still remain in operation today. The mast took on such iconic power during the heyday of the Grand Ole Opry that for many years it illustrated WSM’s letterhead, and its distinctive shape has even been worked into the design of the new Country Music Hall of Fame: The top half of the diamond will tower atop the building’s rotunda, while the bottom half will hang into the hall as a chandelier, Iwhere, fittingly, it will illuminate the plaques of Hank Williams, Loretta Lynn, and the dozens of other stars who relied on the real WSM tower to communicate their music to half the nation.
Before 1932, WSM’s signal beamed out of a flat-top antenna, resembling a laundry line, suspended between two 165-foot towers at Compton Avenue and 15th Avenue South. But in the early ’30s, WSM officials aggressively lobbied the Federal Radio Commission to secure a hard-to-get license for a 50,000-watt signal, and they realized their tower was inadequate to broadcast with that kind of heft.
At the same time, WSM president Edwin Craig hired back an engineer who had been at the controls the night WSM went on the air in 1925. Jack DeWitt, who would go on to run WSM, was the son of a Nashville judge and a teen radio hobbyist so astute that he was asked to build Nashville’s very first radio station, WDAD, on the campus of Ward Belmont School in 1922. After a year or so with WSM, DeWitt dropped out of Vanderbilt’s engineering department when he found they could teach him nothing new about radio, and he went to work for Bell Labs in New Jersey.
When Craig persuaded DeWitt to return as WSM’s chief engineer in 1931, the 50,000-watt RCA transmitter had already been purchased. It was a behemoth with 5-foot-high radio tubes and an elaborate system of pipes designed to cool the tubes with water. But a debate was under way about the best design for a tower. DeWitt told Country Music Hall of Fame historian John Rumble in a 1986 interview that RCA’s engineers recommended another flat-top antenna, but DeWitt had seen a more compelling new design at Bell Labs, built by the Blaw Knox Co. of Pittsburgh. Instead of towers holding up a transmitting wire, the steel tower itself acted as a muscular signal radiator. That meant the tower had to be insulated from the ground, so it made sense, in essence, to weld two tapered radio towers together at their bases, forming a diamond, and set the structure on its tip. Forty feet wide at its middle, the tower is only 2 feet in diameter at its base. Held up by eight insulated guy wires, the mammoth structure sits on a 9-inch-wide rubber and porcelain insulator tested to support up to 3 million pounds.
The soaring height of the WSM towermore than 300 feet taller than the Washington Monumentwas determined by the laws of physics and by WSM’s position on the far left of the radio dial. A signal radiator is most efficient when it is five-eighths the height of the standing wave generated at a radio station’s given frequency. WSM’s spot at 650 kHz makes a wave 460 meters high, so the tower had to be over 800 feet tall. Years later, during some engineering adjustments, 70 feet of the mast at the top of the tower was removed and donated to Lipscomb Elementary School, where it was put to use as a flagpole.
The tower’s diamond shape had another effect that served the Opry well: The lower half, canted toward the earth, laid a powerful ”groundwave“ signal that made WSM brilliantly clear in a wide circle around Nashville. The upper half directed its signal above the horizon line. At night, especially in the winter, a layer of ions in the upper atmosphere becomes a natural reflector of radio waves, and the signal can bounce between sky and earth for thousands of miles. It was this ”skywave“ signal that warmed so many radios across the country and made the Opry a household name.
The author is indebted to former WSM engineer Aaron Shelton, who died in April of this year.
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