Blaw-Knox Diamond Radio Towers

(Jim Hawkins' Radio and Broadcast Technology Page)

Accessed times since March 19, 2001

The Blaw-Knox diamond tower is an icon of broadcast and architectural technology. The WLW page on this site has elicited many e-mails and much discussion as to how many towers of this type exist, where they all are and how long will they remain. Thanks to the many broadcast people who have contacted me and sent pictures and information on these towers, this page became possible. I have found some other sources of information on Blaw-Knox. I will update the page as I learn more. Blaw-Knox is now a product line name of Ingersoll-Rand paving and road surfacing equipment. Thanks to J.T. Anderton and Watt Hairston, who have contributed information to this page. Thanks also to J.T. Anderton, Ed Brouder, Kara Hairston, Ron Lawrence (W4Ron) and Mike Miranda for contributing photos, which appear on this page in addition to my own. I invite others with more information to me. - Jim Hawkins


Some Blaw-Knox History

On March 12, 1906 Blaw Collapsible Steel Centering Company was formed in New Jersey to manufacture and market re-usable steel forms for molding concrete in heavy construction. The initial product line of the Blaw company was based on the patented invention of Jacob B. Blaw of Philadelphia. This invention was for a better way to set the concrete for the sewers than by means of the wooden forms normally used for such work.

In 1909 Luther Knox and Irvin F. Lehman became associated in the establishment of the Knox Pressed and Welded Steel Co. Luther Knox pioneered the use of pressed and welded steel, in place of previously used non-ferrous castings, for the manufacture of water-cooled equipment for open hearth furnaces and for other high temperature applications.

The Blaw-Knox Company name was adopted July 6, 1917, marking the merger of Blaw Steel Construction Company with the Knox Pressed and Welded Steel Company. This merger introduced the company to the steel industry and also brought together the three Lehman brothers into one business firm.

In 1927 the company added radio towers to its products.

During its growth years Blaw-Knox acquired a number of companies. In 1929 A.W. French & Company became part of Blaw-Knox. This was a factor in eventually establishing a complete package of road-building equipment. Blaw-Knox is now a brand name of this equipment and is now part of Ingersoll-Rand.

Blaw-Knox experienced less growth during the years of the Great Depression, but stayed in the black. The company was also involved in the manufacture of many products to support the efforts in WWII, such as: cast armor for naval vessels, turrets for tanks, anti-aircraft Bofors* gun mounts, Naval gun slides and mounts, rockets, projectiles, torpedo launching equipment and the operation of a 16-inch shell line, to name only a few. For it's excellence in the war effort, Blaw-Knox won seven Army-Navy "E" awards with 16 stars.

The company served four basic market categories: (1) the metallurgical industries; (2) chemical process and nuclear industries; (3) public service industries; and (4) public works and highway construction industries. ---

*Bofors is a Swedish company.

One more note of interest is that Blaw-Knox built one of its early manufacturing facilities in Hoboken, PA. The town was renamed Blawnox, PA and is located next to Pittsburgh. (I was born in Hoboken, NJ)

The above information was obtained from a 28 page booklet, published in 1957 entitled: "Blaw-Knox Growth Through Invention And Enterprise," which is the text of an address, given by W. Cordes Snyder, Jr., who was president of the Blaw-Knox company of Pittsburgh, PA. at the time.

The text contains far more details of acquisitions, people and various products, facilities, which are beyond the scope of this page. However, since the address was given in 1957, there is a gap of information which is needed to bridge to it's present part of Ingersoll-Rand. Also, I have yet to find historical information on the decisions and engineering, which led to the design and installation of this type of radio tower. Input is invited.

... Jim Hawkins

Six Stations with Blaw-Knox "Diamonds"

WADO - 1280, New York, NY
5KW (at the time)
This tower was replaced and the
station now runs at 50KW daytime.

Height: 424'

Photograph: Jim Hawkins

WBT - 1110 Charlotte, NC
3 in directional array

Height: 428' each

Photograph: Ron Lawrence - W4RON

(I was informed that some people were cropped
out of the photo. This photo is displayed as

- 1370 Manchester, NH

Heights: Taller of two towers
in directional array,
350'(second tower is 199')

WFEA tower letter

"Attached is a letter from Blaw-Knox
president Nicholas Gerton to William
Foss in Washington. Foss was either
an engineering consultant or an agent
for WFEA's owners in Portland, Maine.
Gerton was explaining the delay in
shipping WFEA's tower and the
letter is dated October 13, 1931.
Ed Brouder
Man From Mars Productions
Photograph: Courtesy of WFEA

WLW -700 Cincinnati, OH

Height: 747'

Photograph: Jim Hawkins
WSM - 650 Nashville, TN

Height: 808'

Photograph: Kara Hairston

WCAU 1210 - Philadelphia, PA

Photograph: Popular Science Mechanical
Encyclopedia, March 1944
WBNS 1460 - Columbus, OH
Photographed in 1998



= Blaw-Knox / 2

This is former WHO 1040 tower. The
leftover bottom half of this Blaw-Knox
diamond is now a utility radio tower.

Des Moines , Iowa

Photo provided by Paul Jellison,
Regional Technical Services Manager
Clear Channel

J. T. Anderton, VP/Managing Director of Duncan's American Radio

"WHO in Des Moines had one until the late 1940's, when it was replaced at the same site by the existing uniform cross-section tower. The bottom two-thirds of the old WHO tower was moved to the rear of an Iowa State Police station in Des Moines for use as a communications tower.

These towers are a special part of radio history. I have visited all of them, and they do make quite a visual impression. Most uniform cross-section towers all but disappear visually against many skyscapes, but not these. Their mass stands out against any color of sky, often resulting in strong visual images. The WLW tower, with the call letters lighted in white at the mid-way point, makes a strong visual impression, especially at twilight."

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

"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-use today. 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.

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.

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."

WBT TOWERS After Hurricane Hugo

(Photo by J.T. Anderton)

This photo of the WBT towers was taken by J.T. Anderton. According to J.T., they remained in that state for a couple of months, while WBT ran on a one-tower special temporary authorization (STA)(10-kw non-DA, as he recalled). The towers were rebuilt exactly the way they were before the damage.

More Hurricane Hugo Damage

(Photos by Mike Miranda - W4DXL (former KD4WKV)

"I worked on air at WBT from 1985 till 1990 and it was a great time. I had listeners from Miami to Montreal, the ultimate ego trip! WBT has a rich history and takes considerable pride in that history. The WBT towers were designed when the station was on 1080. When they broadbanded the antenna system for AM Stereo they electrically shortened the towers with a fence that is perpendicular to the towers and runs around each one. The only place I have ever seen something like that." .... Mike Miranda

Blaw-Knox Ads

"electronics" magazine
June 1940. Pg 46.

"electronics" magazine
Jan. 1941, Pg. 52

"electronics" magazine
May 1940. Pg. 44

"electronics" magazine
July 1940. Pg. 52

"electronics" magazine
Mar. 1940. Pg. 52

"electronics" magazine is a publication of the McGraw-Hill Publishing Company, Inc.

WFEA's Mystery wooden tower

WFEA Blaw-Knox and Wooden Tower "I finally figured out the origins of WFEA's mystery wooden tower. It
was apparently built in 1933 or 34 to accomodate a power increase and a
move from 1430 to 1340kc. It was half the height of the BK tower (which
was referred to in print locally as "the third of its kind" in America).
Between the two towers ran a rope from which a reflector was hung to
protect WSPD in Toledo, Ohio. The wooden tower blew down in the
hurricane of Sept. 1938 and was replaced within 3 months by a John Lingo
199 foot mast as pictured in the photo you have. The BK and Lingo
sticks are still active today though the building is simply a ghost
structure--transmitters but no people."

Ed Brouder
Man From Mars Productions

Products of
The Blaw-Knox Company

As taken from a 1920 Blaw-Knox Transmission Tower Catalog

Fabricated Steel

Fabricated steel, one of the principal products of Blaw-Knox Company, includes mill buildings, manufacturing plants, bridges, crane runways, trusses and other construction of a highly fabricated nature.
A corps of highly trained engineers is maintained for consulting and designing services.

Transmission Towers

Four legged straight line or suspension towers, anchor and dead end towers, latticed and channel A-frames, river crossing towers, outdoor sub-stations, switching stations, signal towers, steel poles, derrick towers.
We specialize in the design and fabrication of high tension transmission lines.

Plate Work

Riveted, pressed and welded steel plate products of every description, including: accumulators, agitators, water boshes, annealing boxes, containers, digesters, filters, flumes, gear guards, kettles, ladles, pans, penstocks, air receivers, stacks, standpipes, miscellaneous tanks, miscellaneous blast furnace work, etc.

Blaw Buckets

Clamshell buckets and automatic cableway plants for digging and rehandling earth, sand, gravel, coal, ore, limestone, tin scrap, slag, cinders, fertilizers, rock products, etc.
For installation on derricks, overhead and locomotive cranes, monorails, dredges, steam,shovels, ditchers, cableways, ships for handling cargo and coal, etc.


Steel form for every type of concrete construction: aqeuducts, bridges, cisterns,. Columns, culverts, curbs and gutters, dams, factories, floors, foundations, houses, locks, manholes, piers, pipe, reservoirs, roads, sewers, shafts, sidewalks, subways, tanks, tunnels, viaducts, retaining walls, warehouses, etc.

Furnace Applicances

Knox patented water-cooled doors, door frames, front and back wall coolers, ports, bulkheads, reversing valves, etc., for Open Hearth. Glass and Copper Regenerative Furnaces: water-cooled standings, boshes and shields for Sheet and Tin Mills.

Links to Other Blaw-Knox Tower Sites
in the World


Lisnargarvey, Northern Ireland built: 1936, and

Lakihegy, Hungary built: 1933, height: 314 metres,
Bernd Waniewski Page: and

Vakarel, Bulgaria built: 1937, height: 352.9 metres, was at
completion second tallest tower of the world, ,

Stara Zagora, Bulgaria

Submitted by Harold Lutz of Germany

Other Tower Pages

Also, for your viewing pleasure, please visit my Cincinnati Star Tower page
The Building of Cincinnati Star Tower by Helicopter


All images are Copyrighted and are provided for your personal enjoyment. Use of these images for commercial purposes including their distribution on CD-ROM or any other media without permission of the owner is prohibited.

Jim Hawkins