Monday, June 17, 2013

WLW And The Blaw-Knox Antenna

WLW Blaw-Knox tower
Ohio Historical Marker:

"In 1922, during the infancy of broadcast radio, the call letters WLW were assigned to the station begun by Cincinnatian Powel Crosley, Jr. The station moved its transmitting operations to Mason in 1928, and by April 17, 1934, WLW had permission to operate experimentally with 500,000 watts. Becoming the first and only commercial radio station to broadcast at this 'superpower', WLW was formally opened at 500,000 watts by President Franklin D. Roosevelt on May 2, 1934. Using its 831-foot Blaw-Knox antenna to broadcast at ten times the power of any station, it earned the title 'The Nation's Station'. Locals reported hearing broadcasts on barbed wire fences, milking machines, rainspouts, water faucets, and radiators. The custom built transmitter, a joint venture between RCA, GE, and Westinghouse, remained in operation until March 1939 when the Federal Communications Commission (FCC) ordered the station to return to broadcasting at 50,000 watts."

On a bitter cold, grey day in March, I passed through Cincinnati on the way back to New York and drove out to the WLW transmitter site in Mason, Ohio. It is just west off I-75. Rounding the bend in Tylerville Road, the WLW tower is probably the most impressive singe tower I have ever seen, as the attached pictures will show.

Some History

In July 1921, Powel Crosley began broadcasting from station 8CR using a 20 watt transmitter at his home in College Hill, Ohio. The WLW call letters were originally licensed to the Crosley Radio Corporation, and in March 1922, Crosley was granted a license to broadcast using WLW at a power of 50 watts. He was assigned two frequencies: 833 KC (kilocycles) for entertainment programs, and 619 KC for weather and farm reports.

In late summer of 1922, WLW moved to Crosley's new manufacturing facility and was authorized to increase power to 500 watts, using newly installed Western Electric transmitters on a frequency of 970 KC. Its antenna was a 140 foot "T"-type cage antenna strung between two towers.

Power was increased again in 1924 to 1000 watts, with a frequency shift to 700 KC, then 710 KC. In 1925, the station was moved to Harrison, Ohio and authorized 5000 watts. In 1927, the Federal Radio Commission relocated WLW back to 700 KC.

In 1928, WLW was granted a construction permit by the commission to raise power to 25,000 watts regularly and 50,000 watts experimentally. By the fall of that year, now relocated in Mason, Ohio, WLW became the first station to broadcast at 50,000 watts on a sustained basis. Four more stations across the US joined in this elite group by the end of the year.

In early 1933, WLW began construction of a new 500,000 watt superpower facility at Mason, Ohio after approval of the Federal Radio Commission. RCA supplied the 500KW transmitter. A new 831 foot, half wave, end-fed, Blaw-Knox double diamond-shaped vertical antenna weighing 136 tons was erected for the small sum (in today's dollars) of $46,000. The wider, middle of the tower structure is 35 ft. square. A concrete lined pond was built in front of the transmitter building for transmitter cooling. Water was pumped through specially designed water cooled tubes, and was then sprayed into the air by fountains, returning back into the pond.

The Blaw-Knox company was a manufacturer of steel structures and construction equipment based in Pittsburgh, Pennsylvania. Today, the company is best known for its unique radio towers, most of which were constructed during the 1930s in the United States. Although Blaw-Knox built many kinds of towers, the term Blaw-Knox tower usually refers to the company's unusual, so-called "diamond cantilever" design, which is held upright by guy wires attached only at the vertical center of the mast, where its cross-section is widest. A 1942 advertisement claims that 70% of all radio towers in the US were built by Blaw-Knox.

On January 1, 1934 the commission authorized WLW to begin using the 500,000 watts on an experimental basis using the call W8XO. An operational license was granted on April 17, 1934 to operate at 500,000 watts at regular hours under the WLW call letters. Under great fanfare, on Wednesday, May 2, 1934, President Roosevelt pressed a telegraph key in the White House which turned on "RCA 1", the WLW transmitter.

WLW was required to cut back to 50,000 watts during the nighttime hours in December of 1934 due to interference caused to CFRB at Toronto, Ontario and other stations. The solution was to erect three 50 ft. anti-skywave phaser towers across the road to cancel out high-angle radiation in that direction. This was the first use of skywave directional control for broadcasting. It worked, and WLW resumed full power.

Superpower WLW was heard virtually around the world.

In 1938, the US Senate adopted the "Wheeler" resolution which resulted in capping high power AM stations at 50 kilowatts due to numerous interference complaints and the desire to establish a path for more locally-oriented stations. Consequently in 1939, WLW's 500 kilowatt broadcast authorization was not renewed, bringing an end to the era of superpower AM radio. The W8XO experimental license for 500 kilowatts remained in effect until December 29, 1942 due to an impending war feeling and the possible need for national broadcasting in an emergency. The 500 kW transmitting equipment was maintained into the 1960s by site engineers, but it was never operated on-air after 1943. Reports have it that WLW was used to broadcast coded communications during the war.

Crosley sold WLW (as well as the Crosley Corporation) to the Aviation Corporation in 1945 at the end of the war.

The WLW Blaw-Knox tower height was decreased from its original 831 feet to 747 feet. When a flagpole was removed from the top of the WLW tower, it was further reduced to 736 feet. The other tower in the background of one of the photos is a backup tower. The lookout tower shown in one photo was manned by armed guards that watched the facility during WWII.


WLW is currently owned by Clear Channel, Inc. and broadcasts an all talk format. The transmitter site remains on Tylerville Rd. in Mason, Ohio.

At least five Blaw-Knox diamond cantilever towers are still standing in the United States:

   WSM-650, Nashville, TN
   WLW-700, Cincinnati, OH
   WBT-1110, Charlotte, NC
   WFEA-1370, Manchester, NH
   WBNS-1460, Columbus, OH

Other Crosley Contributions

Among other notable contributions, Powel Crosley and his brother Lewis were responsible for many "firsts" in consumer products. He was the builder of the Crosley automobiles, the second car radio (Motorola was first), the first push button radio. He developed early radio soap operas, the first non-electric refrigerator, the first refrigerator with shelves in the door, the first to light a major league baseball field. He was the owner of the Cincinnati Reds major league baseball team for many years. Crosley Field, in Cincinnati, Ohio, was renamed for him. Crosley was also chief engineer and later executive vice president of Emerson Radio.


A number of web sites have excellent history on WLW. Two of the best are:

WLW's Big-Arse Transmitter
History of WLW, Cincinnati

Transmitter building

Guy insulator on Blaw-Knox tower

Historical marker

Center section with call letters

World War II guard tower, employee residence, and backup tower


Stephen said...

Interesting article, Bill. :)

So when you were standing next to the tower, how was reception on your various radios of stations near 700 (or 1400) kHz? :)

I'm especially interested in:

690 WZAP Bristol, VA (SE, ~2.4x past 0.15mV/m on radio-locator's map)
690 KSTL St. Louis, MO (W, ~2.5x past 0.15mV/m)
710 WEKC Williamsburg, KY (S, ~1.8x past 0.15mV/m)

680 WHBE Newburg, KY (SW, just within 0.15mV/m)
680 WKAZ Charleston, WV (E, ~2/3 past 0.15mV/m)
720 WGN Chicago, IL (NW, ~10% past 0.15mV/m)

1400 WCYN Cynthia, KY (S, ~30% past 0.15mV/m)

1390 WBLL Bellafontaine, OH (NE, ~40% past 0.15mV/m)
1390 WZZB Seymour, IN (W, ~2/3 past 0.15mV/m)
1410 WING Dayton, OH (N, near 2.5mV/m)

1380 WKJG Fort Wayne, IN (N, ~10% past 0.15mV/m)
1380 WMJR Nicholasville, KY (S, 1/3 past 0.15mV/m
1420 WHK Cleveland, OH (NE, 2x past 0.15mV/m)

1370 WGCL Bloomington, IN (W, ~1/3 past 0.15mV/m)
1430 WXNT Indianapolis, IN (NW, ~25% past 0.15mV/m)

on these radios:
E1, ICF-2010, SRF-M37V, WRX911, DT-400W, PL-600, PL-380, KA321, or whichever ones you had with you. :)

I didn't attempt to use your field strength calculator, as I'm not yet sure how to deal with paths of varying ground conductivity. Any ideas on how to do this?


Hi Stephen,

Actually, I didn't do any monitoring that close to the tower. The radios would have been swamped anyway with too much signal. The selectivity is not adequate to prevent overload or desense at that close a distance. Have been working recently on code to compute varying ground conductivities using the FCC's US M3 map data. The going is slow and I still have more bugs to work out. The total number of recursive calculations almost overwhelms the computer...


Unknown said...

In the early 60's just down the street from the WLW tower there was an
old wooden sign that had a light blub that illuminated the sign.
The light bulb was no longer hooked up to any power, but at night you could see it
was dimly lite do to the static electricity from the tower.


Welcome John,

Thanks for your comments. That must have been quite an interesting sight. I remember using light bulbs for dummy loads in my early amateur radio career. Of course they were wired in!