Working in the field that I do, there are certain things that catch your eye while in a area.

For me, currently being in Nashville. one of those is the historic WSM Broadcast tower.

WSM Broadcast Tower, Nashville, TN

The tower itself was brought in to service in October of 1932. The primary job of this behemoth?

To broadcast the Grand Ol Opry, the longest-running radio program in history, which began as the WSM Barn Dance in 1925. WSM played a major role in the history of American music and radio by broadcasting country music’s signature program over a huge area for decades.

At the time of it’s building, this tower was the tallest tower in America. Standing 878 feet high, it looms over the interstate as you drive by.

It’s still a record holder. Currently it’s the only clear channel Tower that still broadcasts music instead of a news/talk format of broadcast, which it has done since 1979.

AM Towers are built to be “tuned”. Their design attributes to both their frequency and their broadcast area.

Watt Hairston, CE of WSM wrote this regarding the tower:

Blaw-Knox dual cantilevered (center guyed towers). A.k.a. “diamond antenna”. WSM-AM tower I-65 and Concord Road, Brentwood, TN.

Any tower structure exhibits many dynamics that result from gravity, wind and temperature cycles. These forces are constantly at work and result in movements vertically and horizontally of the structure. These movements (even slight) result in tremendous tensions where the structure attaches to a very rigid earth through its foundations. Most specifically the horizontal twisting that results, becomes a formidable “moment”. To compensate for this, either the strength of the structures lower components (where the moving tower meets the non-moving foundation) must be massive enough to compensate for this “moment” or attached to the foundation through a hinge mechanism in the form of a pivot. Thus the tapered base we see on most towers of significant length.

With all this in mind we can reason that for a tower of the height of 808 feet the dynamics (movements) are integral to the mass of the structure. The higher the tower, the size and strength of the lower supports must grow at an un-proportionate rate. If this tower were not tapered, the lower supports (where this twisting moment couples to the foundation) would have to be so large as to make the project extremely costly to accomplish. In the case of AM towers that are electrically insulated from the ground, the problem is magnified because the tower has to rest on porcelain insulators that would be located at the transition to the foundation. The point of maximum force. In a pivot attachment, the moment is not critical because the tower can rotate on its base. This is why tower manufactures use this mechanism to this date. The WSM tower lower half is made up of larger steel members than the top section. Where the bottom taper is linear, the top is not. There is a transition at about the 680-foot level. Eight guy cables are attached at the joining section between the tapers. The entire weight of the tower and the pull of the guy cables rest on a two-section series pivotal Lapp insulator. This tower represents the construction methods and technology at the time. The laws of physics remain unchanged.

The WSM tower was erected in 1932 and began operation from it late that year and is still in-usetoday. The tower was designed and manufactured by The Blaw-Knox Steel Company of Pittsburgh Pa. The original mechanical drawings are very detail. The erection crew was from South Carolina. Originally, the WSM tower was 878 feet tall. This included 758 feet of square structural lattice then 120 feet of tapered mast. By 1939, it was determined the tower was electrically longer due to velocity effect. This contributed to a very high angle of radiation that resulted in a groundwave/skywave cancellation (fade) over Chattanooga some 120 miles distance. This condition was alleviated by this adjustment in height to 808 feet. As a side note, part of the mast was erected as the flagpole for the adjacent Lipscomb School. It was in use there until 1996 when the original school building was replaced. 50 feet of the pole still exist on the top of the tower. It was used to support a turn style antenna for the FM station that WSM operated at this location from 1939 until 1952. The original antenna was in the 45 MHz band. After World War II, the FM allocation moved up to 100.1 MHz. The antenna was replaced with another turn style antenna. That antenna is still up there. WSM relinquished the FM station license in 1952 as television was on the scene and FM broadcasting was no where near profitability.

Picture by John Hettish of Middle Tennessee Two-Way, Inc.

Blaw-Knox went out of the tower business in 1958. There are several of these types of towers still in use besides the WSM tower. The same crew that installed the WSM tower installed the WLW tower near Mason Ohio. In fact, the crew went directly to Ohio when they finished WSM. There are three shorter versions of these towers at WBT in Charlotte, NC. Blaw-Knox built taller towers as well. The WSMV-TV tower is 1369 feet tall and has a 12-foot width face. This tower supports the antennas of WSMV-TV, WSM-FM and WZTV-TV. It is the classic pivotal base sectional guyed tower.

Prior to using the Blaw-Knox tower, WSM used a “cage” type antenna that was supported by two self-supporting towers. A wire was strung between the towers and a vertical feed wire fed the center from a tuning house directly centered between the towers. This was also referred to as a “flat top” antenna. Dr. George Brown et. al, of RCA fame, impressed the FRC with his vertical, series fed antenna that used 120 quarter wavelength radials as 360 degree counter-poise. There have been no improvements on this design to date. Dr. George Brown (like Blaw-Knox) is deceased.

Picture by John Hettish of Middle Tennessee Two-Way, Inc.

There has been some suggestion that the Blaw-Knox tower was designed to be “fat” in the middle to accommodate a current loop (I max) in a 1/2 to 5/8 wave length tower. This was purely consequential and was not a consideration in the design of the tower.

W. Watt Hairston (N4UHE)
Chief Engineer
WSM
Nashville, TN.

The tower itself puts out over 50,000 watts at 650 Kilohertz.

It’s been a feature in American history, although while a backstage a player, a player nonetheless. As a tribute to the station’s centrality in country music history, the diamond Blaw-Knox antenna design was incorporated into the new Country Music Hall of Fame and Museum’s design in 2001. It was also part of the CONELRAD US National Emergency Plan in the event of a nuclear war.

Among the many people who have been affiliated with station Ralph Emery, Larry Munson and Pat Sajak are probably among the best known