SPRINGFIELD, VA.—Ever since Marconi began playing with radio at his family villa, there have been many variations on a theme when it came to transmitting antennas. Very early antenna design was rather simplistic: “Get as much wire up as high in the air as possible and tune for maximum spark or current.”
When radio broadcasting arrived in the early 1920s, virtually all stations adopted the horizontal long-wire antenna design favored by ship-and-shore radiotelegraphy operations. These radiators took the form of either a “flattop” with parallel multiple wires supported by cross arms, or a “cage,” with the ends supported by rings to create a cylindrical configuration. These arrays were suspended by self-supporting towers and were commonly located on tall buildings (collocated with the station’s studios). These antennas were typically linked to the station transmitter by a bundle of multiple conductors attached either to the middle (“T”) or at one end (“L”) of the horizontal wires. [See Reference 1.]
It seems to have escaped notice early on that these feeders were neither balanced lines nor wire-type coaxial cables, it was really the feeder that did most of the radiating; the horizontal wires above it basically amounted to top-loading.
According to Ron Rackley of duTreil, Lundin & Rackley Inc., this wire antenna trend can be traced to AC power distribution theory that carried over into early radio engineering.
“Most early radio engineers were trained in power systems design rather than in field theory,” said Rackley. “There was actually a controversy at the time, with many engineers believing that larger antennas wouldn’t radiate as well [as smaller ones], because if you increase the height, the antenna current goes down because the resistance goes up. A man named Stuart Ballantine showed mathematically that taller antennas produced increased horizontal plane radiation. He was doing calculus and showed that if you integrated current over a larger vertical span, you get more current. He published his paper in 1924 [2] and this started changing things.”
Prior to the adoption of the insulated-base vertical radiator, multiple-wire horizontal antennas were the de facto means for coupling RF to free space. The current FCC logo design incorporates the venerable flattop and its feeder system.INSULATED-BASE VERTICAL RADIATOR
Based on Ballantine’s findings, some pioneer stations did reexamine antenna effectiveness and began experimentation. New York’s WABC (now WCBS) was one of these, and erected what is believed to be the world’s first medium-wave insulated-base vertical radiator in nearby Patterson, N.J.
This radical departure from existing antennas created something of a sensation among radio practitioners and the WABC installation rated a cover story in the November 1931 issue of Radio-Craft magazine.
As described in the article: “This ‘mast-antenna’ (a new term in radio) is part of a new 50,000-watt transmitter … and is a new type of broadcast aerial construction which breaks away from tradition, and establishes a precedent.”
The story noted that in addition to providing a non-directional pattern (not possible with horizontal wire antennas) the new “mast-antenna” also concentrated more energy into the ground wave to provide better local area service.
The vertical radiator got high marks from Jack DeWitt, WSM’s legendary director of engineering, who had left a position at Bell Labs to take the WSM job just as that station was readying for 50 kW operations. DeWitt was able to convince management to dump the flattop that RCA had specified for the installation. In a 1982 interview, he recalled:
“Bell Laboratories was in the business of designing radio transmitters and studio equipment [and] now, they wanted a good antenna to recommend to purchasers of their equipment. Dr. Stuart Ballantine … pointed out that there was no point in putting up separate towers and stringing antennas between them because the towers could only be a problem due to the currents induced in them from the antenna and it would distort the pattern. Why not use the tower [itself]? Bell then went to the Blaw-Knox company in Pittsburgh and had them design a tower which would have low capacitance. The first one of those towers was put in at Wayne Township, New Jersey for the Columbia Broadcasting System. Strangely enough, I worked on that installation.”
WABC’s new 1931 transmitting plant included a half-wave vertical antenna, marking a radical departure from conventional horizontal wire antennas; however, the vertical radiator was slow to be adopted by the other medium-wave broadcasters.
(Click to Enlarge)This closeup view shows one of the multiple large insulators used to electrically break the WHK masts into non-resonant sections. The integrated insulated tubing for breaking up the copper gas line is visible on the right side of the insulator. The special “jack-knife” ladder is seen immediately at the right of the insulator.
(Click to Enlarge)
PHOTO CREDIT:
Cleveland Broadcast Radio ArchivesBREAKING FROM CONVENTION (SORT OF)
About the same time that the vertical radiator was being readied for prime time, WHK, a pioneer Cleveland, Ohio station, was having second thoughts about the “conventional” flattop antenna they’d been using since commencing commercial operations in 1922. Its studios and transmitter plant were collocated in a downtown high-rise building, and as the 1920s drew to a close the station’s management, and its chief engineer E.L. Gove, were became increasingly concerned about coverage problems:
“A careful study of the range of WHK, Cleveland, Ohio, revealed the fact that the field pattern was decidedly ragged in certain areas of the city. From this and other investigations it was quite apparent that the station, situated on the top floor of a Cleveland office building, surrounded on all sides by other skyscrapers and broadcasting on a power limit of 1,000 watts, was by no means operating at its highest efficiency.”[3]
Gove concluded that the poor coverage was due to the rooftop transmission plant employed by the station — specifically, the presence of other nearby high-rise steel framework buildings, a poor ground system and power loss from re-radiation by the flattop’s supporting towers.
The solution appeared simple: Relocate the transmitting plant!
“After considering the problem from all angles it was decided to petition the Radio Commission for permission to move the transmitting apparatus into the country where it would be possible to put in an effective ground system, and where there would be no interference from steel girdered buildings.”[4]
A search of retired Federal Radio Commission records for the station did not disclose the referenced “petition,” but it was most likely filed in 1929.
Inside the building (and below the station ground plane), this Western Electric transmitter excited the flattop radiator 185 feet above.
PHOTO CREDIT:
Cleveland Broadcast Radio Archives WHK acquired property about nine miles south of Cleveland for the new facility and proceeded to construct what was to become perhaps the most unusual transmitting plant ever built, as the station elected not to adopt the new vertical radiator technology, but rather to stick with the “tried and true” flattop. The idea was to make it perform better.
THE NEW (AND RADICAL) WHK ANTENNA
Gove correctly identified the rooftop antenna supports as major contributors to the station’s poor coverage and was determined to do something about this at the new site: employ flattop support masts that did not re-radiate. Wooden towers of the desired height — 185 feet — were apparently ruled out as impractical, and Gove enlisted the services of Arthur O. Austin, chief engineer at the Ohio Brass Company’s insulator division, to develop a way to break the steel masts into non-resonant sections, just as was done with the guy lines at the new WABC installation.
Austin had been previously granted a patent for sectionalizing high-tension power line support towers and was a logical choice for the WHK mechanical engineering tasking. He was later granted another patent for the design of the WHK isolated section towers. [5]
Fabricating the necessary insulators posed no real problems; however, there were still issues to be resolved.
Arthur O. Austin received a patent for the design of the special WHK antenna supports.
(Click to Enlarge) One of these was access to upper tower sections for maintenance. As it would have been unwieldy and dangerous for riggers to climb over or around these big hunks of glazed ceramic, Austin devised what was referred to as a “jack-knife” ladder system, with ladders pivoting to an open position when not in use to maintain isolation of tower sections. He also engineered a means for breaking the steel winch cables used to hoist up the flattop into non-resonant lengths.
AN UNUSUAL LIGHTING SYSTEM
The real engineering challenge was in lighting the new masts to warn aircraft pilots of their presence at night.
Radio tower lighting was in its infancy then, for as mentioned, most antennas were installed on high buildings, which had their own warning lights.
With the new breed of insulated-base vertical radiators (and the WHK sectionalized masts), a major problem arose — lighting power conductors would shunt RF to ground, or in the case of WHK, ground the RF and defeat the purpose of the isolated tower sections.
WABC made their 665-foot tower visible at night with powerful ground-mounted floodlights illuminating the mast, building and surrounding acreage.
Other schemes were also proposed for lighting this new breed of medium-wave antenna. [6]
One involved outlining the structures with neon tubing energized by the tower’s RF. This would have required all-night operation though, something that few stations did then. Another approach was the use of a motor-generator set, with the generator mounted on the tower and separated from the ground-mounted motor via an insulated shaft. In theory, this could have worked at WHK, but would have required multiple generators, as AC (or DC) lines couldn’t cross tower section insulators, and some very, very long insulated shafts.
Eventually WHK gave up on flattop antenna technology and reworked the 1931 supporting masts into “conventional” vertical radiators. This 1944 photograph shows the “after” version with capacity hats added to the original structures. The station had also gone “directional” and added a third tower. Close examination shows the insulators used to isolate the upper sections have been bypassed and conventional lighting installed. The photo also reveals that the bottom-most tower sections are still isolated from the upper portions, with a “feeder box” (or perhaps an ATU) located at the top of the lowest section. Multiple conductors emerge from this unit and connect to all four mast legs.
PHOTO CREDIT:
Cleveland Broadcast Radio Archive A slightly saner approach would have been the use of chokes designed to pass low-frequency AC lighting current, while presenting a high impedance to RF. This approach was successfully adopted for insulated-base vertical radiators, but would not have been practical at WHK due to the number of tower sections that had to be isolated from each other.
Austin and Gove finally settled on a lighting system that did not depend on electrical power at all.
A gas line was brought up to the tower bases and a tubular porcelain insulator was used to connect this to a copper line running along the periphery of each tower section. The line was broken again at each the tower section via non-conductive passageways incorporated into the tower section insulators. Gas was flared at various levels of the towers to identify them to night-flying aircraft.
One can’t help but wonder what nearby inhabitants and aircraft crews and passengers thought about these two 185-foot “burning men.” One can’t help but wonder, too, what sort of gas bill this lighting system generated, as the gas jets would have had to flare 24/7. Relighting them every evening would not have been practical.
Looking back 80-plus years, another aspect of the “new” WHK transmitter plant is also quite interesting. The two-story transmitter building was constructed with its lower eight-and-a-half feet set below ground level. According to the surviving document, this was done so that the top of the transmitter was at the level of the ground system. Readers can draw their own conclusions about this bit of engineering.
An Austin “ring transformer” couples AC lighting power on to this modern AM vertical radiator. Did A.O. Austin invent it due to the difficulty in lighting WHK’s 1931 towers? Austin’s tower patent also describes the use of a heating system (either gas or resistance heaters powered by storage batteries) to keep the sectionalizing insulators dry and minimize losses. It is not known if this amenity was included in the WHK installation.
Quite an unusual transmitting plant!
By the way, while Arthur O. Austin is not really well known for inventing the sectionalized radio tower; he is remembered for his later invention of the “ring transformer” for passing AC to insulated base radiator lighting systems without shunting RF to ground. Undoubtedly, his experience with WHK led him to invent this special transformer that bears his name and is still used today.
Special thanks to Ron Rackley, Ludwell Sibley, Frank Foti and Mike Olszewski for assistance.
James E. O’Neal is technology editor for Radio World sister publication TV Technology. Find past history articles by scrolling the Roots of Radio tab under “Columns” at radioworld.com.
REFERENCES
[1] Chamberlain, A. B., and Lodge, W. B., “The Broadcast Antenna,” Proceedings of the Institute of Radio Engineers, Vol. 24, No. 1; Jan. 1936, p. 13.
[2] Ballantine, Stuart, “On the Optimum Transmitting Wavelength for a Vertical Antenna Over Perfect Earth,” Proceedings of the Institute of Radio Engineers, Vol. 12; Dec. 1924, pp. 833-839.
[3] “Station WHK introduces important refinements into radio transmitting,” (author not named), Radio Engineering magazine, Aug. 1931, p. 21.
[4] Ibid, Radio Engineering, Aug. 1931.
[5] U.S. Patent No. 1,968,868, “Radiotower,” filed Feb. 16, 1930; granted Aug. 7, 1934.
[6] Gunsolley, Verne V., “Radio Tower Tuning and Lighting,” Radio Engineering magazine, June 1932; pp. 7, 8, 12.
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