(click thumbnail)Loy E. Barton and one of his giant sunflowers. Courtesy Sarnoff LibraryFor several years now, I’ve done a straw poll in the radio hall at the NAB convention, stopping passersby and asking them if they had ever heard of Loy Edgar Barton. I’ve made it a point to ask the silvery- or white-haired crowd, not kids who appeared to be fresh out of school.
To date, no one has been able to offer a clue to Barton’s identity and his place in the history of radio.
To save a little time, I’m going to go ahead and give away his secret. He was the individual who set forth the principle of high-level Class B plate modulation.
This was in the early 1930s. From then on, virtually all of the medium- to low-power AM transmitters (and even some of the high-powered rigs) used anywhere in the world were Class B plate modulated.
Barton’s modulation scheme set the standard for nearly five decades of AM radio, until solid-state transmitters and some radically new modulation techniques began to dethrone it in the late 1970s
Most all of us associate Armstrong with FM; Colpitts and Hartley with oscillators; de Forest with the vacuum tube; Yagi and Beverage with their antennas; and, if you’re really into this sort of thing, perhaps Black with negative feedback.
Barton’s name draws no such recognition and he’s mentioned in few radio engineering books.
F.E. Terman’s 1937 “Radio Engineering” does cite Barton in a section on Class B amplification, but he’s nowhere to be found in the chapter on modulation. Even Andrew Inglis in his otherwise excellent 1990 broadcasting history book, “Behind the Tube,” slights Barton and his accomplishment. Inglis presents Barton’s modulator circuit while describing the work of another inventor. In fact, Barton really doesn’t appear to be associated with the science of radio at all.
How is it that Barton and an accomplishment as important as Class B plate modulation could be completely overlooked and forgotten?
Barton’s story properly begins in what is recognized today as the very infancy of broadcasting, that period in the early 1920s when the public at large was introduced to radio.
FESSENDEN AGAIN
More than 15 years earlier, Reginald A. Fessenden developed the world’s first AM modulated transmitter. He did it very simply and with the materials available to him, simply connecting a carbon microphone in series with the transmitter’s antenna circuit.
Sound waves caused the resistance of the microphone element to vary and the varying resistance produced a change in antenna current: AM!
However, there were some real drawbacks to this technique. First, as there was no amplification, it was not very efficient; i.e., there was not that much change in antenna current with reasonable audio levels. About the best depth of modulation that could be achieved was perhaps five to 10 percent.
Second, as the microphone was passing all of the antenna current, it got quite hot. Fessenden solved this problem to some degree by using platinum-iridium electrodes and water cooling.
RAYMOND HEISING
(click thumbnail)Heising modulation (adapted from Barton’s 1925 thesis drawing).
It took several more years and a Bell scientist named Raymond Heising to develop a much improved modulation scheme.
Heising modulation, or constant current modulation as it is sometimes know, can best be explained by referring to Fig. 1, which is adapted directly from Barton’s master’s thesis document.
The plate of the modulator tube is tied to the plate of the RF amplifier (actually a power oscillator, as was state of the art at the time) with a common iron core choke supplying DC potential to both. As audio input level to the modulator tube rises, the tube tries to draw more plate current, but the inductor tends to resist this change and the plate voltage drops. (The inductor is trying to maintain a constant current flow.)
As the common plate voltage drops, the RF amplifier gets less of its share and antenna current is reduced. As the audio level drops, things start to get back to normal with the modulator plate current requirements dropping off. Again the change in current is resisted by the inductor and this turn lets the RF amplifier plate potential rise, increasing antenna current.
Heising’s circuit became the basis for most all early broadcast transmitters, with Western Electric either manufacturing them or licensing the technology to other vendors.
Enter Loy Barton.
Barton was an Arkansas native who entered engineering school in 1917 in a Land-Grant school located in his home town. This was the University of Arkansas in Fayetteville. After receiving his bachelor’s degree, Barton worked for a while as an instructor in mechanical engineering at the school.
He was keenly interested in electricity and radio and went on to pursue advanced studies in this field. By 1924, he was ready to take on a “hands-on” practical engineering project that was part of the college’s graduation requirement.
A “Cinderella” project was offered by the faculty and Barton was quick to take it on.
A few years earlier, the school has contracted with a commercial firm to build a campus radio station. What was delivered was a rather crude 100 watt transmitter that proved far from satisfactory. The engineering faculty felt that the best solution was a new 500 watt transmitter constructed “in house” and under their auspices. Barton was given a budget and the task of designing and building everything from the microphone pre-amplifier to the antenna.
A copy of Barton’s thesis details the areas of power supplies, antenna and counterpoise, audio amplifiers, oscillator, and of course, the modulator. Barton was more intrigued with the modulator circuitry than with anything else and begins his thesis with a thorough analysis of the state-of-the art Heising modulator.
He concludes several things. First, as the iron core inductor sourcing plate voltage to both the modulator tube and RF amplifier (power oscillator) will never allow the RF amplifier plate voltage to drop to zero, or on the other swing, double plate voltage, 100 percent modulation of the carrier is impossible.
Second, the circuit is grossly inefficient, as the audio amplifier single-ended and has to be operated in class A mode. To compound the problem, this class A audio amplifier has to develop as least as much power as the RF amplifier that it modulates! (This was carried to the extreme with Western Electric’s early Heising modulated 50 kW transmitters — AC input power was in the neighborhood of 250 kW!)
GENIUS
(click thumbnail)The 11-foot modulation transformers used in the WLW 500,000 W plate-modulated transmitter. Image courtesy Charles Stinger, AWA.
Barton has a stroke of genius as he analyzes the Heising circuit and states in his thesis:
“Therefore, it is impossible to get 100% modulation, or apparently approximat (sic) to it, unless there is considerable power in the modulators. The above discussion has suggested to the writer the use of a transformer instead of the choke XL with the modulator plate circuit through the primary and the oscillator plate through the secondary.”
That is, if the choke were to be replaced by a suitable transformer with the input side forming the audio amplifier plate load and the secondary providing plate voltage to the RF amplifier, transmitter modulation might be considerably bettered.
However, Barton continues, “The writer will not have the time to test or try the idea for this paper.”
The new school station (KUOA) ultimately was a success, with reception reports coming from all over the United States and the Caribbean. Barton received his degree and departed for Schenectady and a job at General Electric.
After a couple of years battling the upstate New York climate and the corporate structure of GE, Barton decided that the job was not his true calling and returned to Arkansas, where he hired on back at his alma mater as an assistant electrical engineering professor.
The modulation improvement idea developed during his thesis work kept haunting him and before long he was able to get funding for construction of a special transformer needed to test his idea (the world’s first plate modulation transformer). The 600-pound transformer arrived and KUOA’s transmitter was reworked with it. As predicted the (now) one kW rig’s depth of modulation and operating efficiency were greatly enhanced.
Barton, then an associate professor of electrical engineering, published his findings in an obscure little journal, the University of Arkansas Bulletin, a tome more at home with papers on such topics as “Origin and performance of principal cotton varieties in Arkansas” or “Problems relating to the fabrication of building boards.”
Barton’s modulation paper appeared in the edition dated May, 1930 — Bulletin No. 8, under the unassuming title “A Plate Modulation Transformer for Radio Stations.”
One has to question why Barton and the university would allow something this revolutionary to go virtually unnoticed. Perhaps it was that the Great Depression had arrived in full form and there wasn’t money available for attorneys and a patent filing. Perhaps no one in the school really understood the significance of what Barton had done and that there was some real money to be made with the invention. Perhaps Barton was modest and didn’t think that what he’d done was really that big a deal.
Nearly 80 years have passed since that first transmitter went on the air with Class B plate modulation and none are left who might have been able to shed some light.
OFF TO CAMDEN
Somehow the troops in Camden got word of Barton’s modulator. Shortly thereafter he left Fayetteville and academia for South Jersey and the Radio Corporation of America.
Barton’s modulator circuit and modulation methodology were offered up to the patent office in Jan. 1932 and he eventually received U.S. patent number 2,063,290 under the rather deceptive name “Radio Signaling System.”
It’s a given that the patent was assigned to RCA.
It was typical in those days for companies such as RCA and Western Electric to reward employees for patent assignments with tokens such as $50 savings bonds.
(click thumbnail)High-level Class B plate modulation circuit (adapted from Barton’s article in the 1930 University of Arkansas Bulletin).Of course, working for such a company as RCA offered perks that were not monetary. A very big project was brewing there in the early 1930s. Not content with a mere 50,000 watts at Cincinnati’s WLW, owner Powell Crosley Jr. placed an order with RCA for a one-half megawatt machine. Class B high-level plate modulation would be used in its construction and ownership of Barton’s patent would come in quite handy. One must speculate that it must have been very satisfying for Barton to witness such a scaling up of the modulator he built for the one KW rig back in Fayetteville. This time it was a 400,000 W push-pull Class B audio amplifier, built around eight of the awesome UV-862 100 kW water-cooled tubes and two 11-foot tall, 50-ton modulation transformers.
Barton published several articles in the RCA house publication, Broadcast News. In his first article on modulation in June, 1935, the editor added a note to Barton’s article with the information, “It is significant that Loy E. Barton is the originator of Class B Modulation, having started his development of this system while he was instructor in the University of Arkansas. He has contributed greatly to the present Class B Modulation system employed by RCA, and is considered the outstanding authority on the subject of Class B and other types of Modulation. — Ed.”
RADIO-POWERED CAR
Once the giant transmitter was up and running and had settled into some degree of reliability, there was time for a little idle thought and daydreaming.
For Barton, this was in the form of a memo dated March 1, 1934 and addressed to his supervisor, I.R. Baker. In what even 70 years later reads like science fiction, Barton lays out plans for a radio-powered car.
“Some time ago I suggested to you and Mr. L. F. Jones the possibility of picking up enough energy from the WLW antenna to operate a car along the highway near the new WLW transmitter. I have checked with Dr. (George) Brown, of the Research Division, as to the probably (sic) energy pickup at distances of up to about one-fourth mile from the antenna … The results of the preliminary consideration of the problem indicate that about 200 watts may be picked up on a loop at distances up to one-fourth mile and that circuit arrangements can be devised to supply power to a 1/8 horsepower motor.”
Barton went on to speculate that it might be possible to construct a vehicle from a stripped Austin chassis capable of carrying one person at three to five mph on level pavement. He admitted that such a vehicle would serve no useful purpose other than for publicity, concluding, “The cost of construction and demonstration of such a car will, I believe, be quite small as compared to the publicity derived …”
As there’s no record of such a car having been built, Barton’s argument probably didn’t win over any of the top brass at RCA. There would also be the matter of a suitable rectifier, as silicon diodes were some three decades in the future.
Barton’s career did stretch into that solid-state future and by the 1950s he was designing transistor radios and other semiconductor circuitry with the best of them.
Barton continued his career track at RCA and along the way produced a few more patents; his name appears on a total of 83.
His interest in modulation and Class B operation never waned and he published articles on these subjects in RCA’s Broadcast News, Proceedings of the IRE and the amateur radio publication QST, among others.
COLOR BURSTMore InfoThe author used the following sources for this article, which may be of interest to those who wish to learn more about the topic.
(1) U.S. patent no. 2,594,380
(2) Baker, I.R., “A Visit to the New WLW”; (RCA) Broadcast News, Feb., 1934.
(3) Barton, Loy Edgar, “The Design, Construction, and Operation of the 500-Watt Broadcasting Station of the University of Arkansas”; thesis submitted May 13, 1925
(4) Barton, Loy E., “High-Power Audio from Relatively Small Tubes”; Proc. of the IRE, July, 1931
(5) Barton, Loy E., “Application of Class B Audio Amplifier to A-C Operated Receivers”; Proc. of the IRE, July, 1932
(6) Barton, Loy E., “Class B Audio Amplifier as Modulator For Broadcasting Stations”; Radio Engineering, July, 1933
(7) Barton, Loy E., “Modulation System For Transmitters”; (RCA) Broadcast News, June, 1935
(8) Barton, Loy E., “Some Further Thoughts on Modulation”; (RCA) Broadcast News, Dec., 1935
(9) Barton, Loy E., “Recent Developments of Class B Audio and Radio Frequency Amplifiers”; Proc. IRE, July, 1936.
(10) Brown, George, “And Part of Which I Was,” Princeton, J.J.; Angus Cupar Publishers, 1979.
(11) Poindexter, Ray, “Arkansas Airwaves,” Cassville, Mo.; Litho Printers, 1974.
(12) “Did WLW Propel A Car? — Telecommunication,” edited by Don DeNeuf, The Old Timer’s Bulletin (Antique Wireless Association publication), May, 1990.
In the early 1950s, Barton was a member of the group that worked round the clock to develop compatible color television. (Barton shared the patent for the principle of the color synchronizing burst with Peter Werenfels.)
Barton still had roots in Arkansas and occasionally returned to his home town to visit relatives. He also felt strong ties to his school and never missed an opportunity to stop in and visit former associates and to guest lecture engineering classes.
Jim Haynes, an engineering student at the University of Arkansas in the 1950s, recalls Barton appearing on campus several times.
“He popped in one day and lectured to us about this new solid state device he referred to as the ‘thyristor,’” Haynes said. “It was so new that few of us had heard about it. I had read something about a silicon-controlled rectifier though, and I finally put the two together.”
Haynes recalls locating and moving the special modulation transformer that Barton had designed in 1928.
“Around 1957, one of the professors recognized it in a storage closet and we all thought it could be put to good use in the school’s ham station, K5YM,” said Haynes. “It was extremely heavy and I don’t think that we could have gotten it up to the third floor shack without the freight elevator.”
The planned modulator was never constructed and the ham shack and transformer continued to move around the campus until the latter finally disappeared, possibly falling victim to a scrap yard or local landfill.
Barton retired from RCA in the mid-1960s after some 35 years with the company. (Patent records indicate that in the late 1930s he defected for a couple of years, going across the Delaware River to work for rival Philco.) His career spanned the startup of the earliest broadcast stations all the way to the invention of the chip.
RCA continued to sell Class B plate modulated transmitters into the last decade of that company’s existence. There is no record of the amount of money that Barton’s patent produced for RCA through transmitter sales and licensing agreements, though it had to have been substantial.
Barton continued working and inventing practically to the end. His last patent was issued after his retirement from RCA and dealt with textile mill machinery.
Not a great deal is known about Barton’s personal life. However, a 1960 article in the University of Arkansas’s Arkansas Alumnus magazine provides a bit of information in an article titled, “What College Did For Me.”
The 62-year-old Barton wrote: “In fact some make up for the things they could not do as students back in the days when money was scarce … To compensate for the lack of social activity, I now have the time and money to do some of the things I wish I could have done in college. For example, I am learning to dance. I will be retiring in three years and I am making an effort to be ready for the new venture.
“When I started college the one thing that helped me the most was that I was not afraid of work and had plenty of courage. In fact, the principal reason for taking electrical engineering was that it was reputed to be the most difficult course in college.”
In the article, Barton recalled that the “best boost anyone could ask for” was his development of the Class B amplifier and its use in high-level modulation. He estimated then that more than 90 percent of broadcasting stations were using his modulation technique.
Loy Edgar Barton died in 1986 at the age of 89.
So, from now on, when you think about Class B amplifier operation and especially the utilization of Class B for plate modulating AM rigs, think about Loy Barton. Even though high-level Class B plate is nearing its 80th birthday and has been largely replaced by other methodologies, I propose that from here on it be referred to as “Barton modulation.”
Special acknowledgement is given to Jim Haynes for his assistance in preparing this article. Haynes published an article about Barton in the June, 2003 issue of Electric Radio magazine.
