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The First AM Broadcast

Reginald A. Fessenden

Reginald Aubrey Fessenden was the first person to broadcast with an amplitude modulated sine wave. In light of the technology and attitudes of his time, it was a remarkable accomplishment.

His initial broadcasts took place between December of 1906 and July of 1907.

In order to succeed, he needed to create an entirely new system of sending and receiving wireless signals. He knew that Marconi’s method of sending short and long burst of electrical noise was inadequate. He also knew that Marconi’s coherer would never work as a detector of voices and music.

Fessenden was among the first, if not THE first, to know that high frequency continuous waves were the only practical way to send information over long distances without wires. And for quiet, distortion-free telephony to be possible, he knew that he needed perfect sine waves, not the hash produced by arc or high-speed quenched-gap spark transmitters.

It was Fessenden who convinced General Electric to build the Alexanderson alternators that he used to create the radio frequencies that carried his first broadcasts.

Fessenden designed special microphones to amplitude modulate the transmitter’s high frequency electrical currents.

At the receiving end he developed the “Liquid Barreter,” the first detector capable of separating audio frequencies from the carrier frequencies.

For his achievements as the creator of the first AM radio broadcasts, Reginald Aubrey Fessenden is regarded as “The Father of Modern Radio.”

As early as 1899, while the rest of the world was still anticipating the wonders that Marconi and his system of wireless were about to reveal, Fessenden was already convinced that sending dots and dashes in the form of short and long bursts of static was obsolete.

Alternating current had already arrived in the field of electrical power; Westinghouse put A.C. generators on Niagara Falls in 1895. Tesla had actually built an alternator capable of producing 15,000 cycles per second as early as 1890. The transition to high frequency, alternating current radio signals should have been the natural next step.

But to transmit voices over the air, Fessenden felt that he needed an alternator capable of delivering 150,000 cycles at 25,000 watts. In 1900, he contacted George Westinghouse and asked him to build one. After Westinghouse turned him down, Fessenden turned to Charles Proteus Steinmetz of General Electric. Fessenden suggested that he could help Steinmetz design such a machine, and eventually purchase forty or more of them.

Marconi Coherer at Museum
Donated by Doug Whitney

But even if Fessenden could build an alternator capable of the output that he envisioned, he would need some kind of detector at the receiving end. Until Fessenden's discovery of the "Liquid Barretter" in 1902, the primary detector used in wireless work was the coherer, a crude device incapable of recognizing anything but short and long bursts of energy.

Illustration "C" above2 is a de Forest "Spade Detector." The platinum wire was sealed in a small glass tube drawn down to a point at one end, primarily to conceal its similarity to Fessenden's design. Fessenden sued, and "in 1906, after three years of litigation, de Forest was denied use of the spade detector and assessed damages for infringement."3

Fessenden chose the term "barretter from an old French word meaning 'exchanger' since it changed alternating current into direct current."1

The Liquid Barretter became known as the electrolytic detector and from a distance it resembled a crystal detector, in both scale and construction. In place of the "cat's whisker" was a fine platinum wire that just broke the surface of a small cup of acid solution, either nitric or sulfuric. This contact created a small electrolytic condenser that placed a high resistance to current in one direction but not in the other. By the time of his 1906 broadcast, many of the Navy's ships were equipped with some form of Fessenden's detector, although many were copies marketed by de Forest as the "Spade Detector."

To develop the kind of wireless system he envisioned, Fessenden needed financial backing. The world was not ready for the concept of broadcasting. Wireless communication was viewed simply as a means to an end; getting information from one point to another. The fact that unintended listeners could "tune in" was a detriment, not an asset.

By 1902, his radio patents, successful demonstrations, and outspoken authority enabled him to secure the backing of two wealthy Pittsburgh businessmen, Hay Walker and T.H. Given. Together, they formed the National Electric Signaling Company (NESCO); just in time, it appears, for in March of 1903 the first G.E./Steinmetz/Fessenden alternator arrived. Providing only 10,000 cycles per second at low power, it was a big disappointment. Ever resourceful, Fessenden "connected its output to a spark gap and used the spark to excite the antennae. By 1904 NESCO was advertising wireless telephone sets using this combination for commercial sale, with a guaranteed range of twenty five miles."4

1906 Alexanderson/Fessenden Alternator5

The heart of the 1906 transmitter was another General Electric alternator, this time designed by Fessenden and the brilliant young Swedish engineer, Ernst Alexanderson. The principal difference between the Steinmetz and Alexanderson models was that Steinmetz used a conventional rotating armature with coils attached that tended to disintegrate above 3,800 revolutions per minute, while Alexanderson used a fixed armature winding and a stationary field coil suspended between two rotating steel discs. The rotating discs had "teeth" cut into them that caused the lines of flux to alternately rise and fall, thus inducing an AC voltage in the armature windings. Perhaps the oddest feature of the new design, however, was a wooden armature. Fessenden, convinced that iron would be subject to large hysteresis and eddy current losses, especially at radio frequencies, insisted that the windings be placed in wood.

The “Alexanderson/Fessenden” alternator was "shipped to Fessenden's experimental station at Brant Rock, Massachusetts, in late August, 1906 and after minor delays, due to a bent shaft and lack of a suitable drive motor, was connected to the antenna system and put on the air. The frequency could be raised no higher than 76kHz, and the output power at that frequency was less than 50 watts instead of the 250 that had been hoped for. But these were problems of development and refinement. As far as Fessenden was concerned the major victory had been won. He and the engineers of General Electric had done what Fleming and other advocates of the spark system had called impossible; the problem of generating continuous radio waves mechanically, at significant power levels, had been solved. There was reason for euphoria."6

Subsequent Alexanderson designs used a single rotating disc that spun inside a fixed armature and field assembly wound on iron laminations. Slots around the circumference of the rotor were filled with phosphor-bronze wire to minimize the effects of wind-friction and noise.

The illustration (at left) of a 1909 Alexanderson alternator shows how it was connected. The Magnetic Saturation Coil (M) acts as a variable shunt across the RF signal.


1) Hugh G.J. Aitken, The Continuous Wave, 1985, Princeton University Press, p. 56.
2) Rupert Stanley, Textbook on Wireless Telegraphy, 1917 Longmans, Green & Company, London, p. 235
3) Tom Lewis, Empire of the Air, 1991 Harper Collins, p. 49.
4) Aitken, p. 65.
5) Illustration of alternator from: Ernst Alexanderson, Alternator for 100,000 Cycles, presented at the 26th annual convention of the American Institute of Electrical Engineers, Frontenac, New York, June 28, 1909
6) Aitken, pp. 69-70.

Fessenden Timeline

1866: Reginald Aubrey Fessenden was born on October 6, in East Bolton, Quebec, Canada. He was the eldest of four sons of Elisha Joseph and Clementina (Trenholme) Fessenden. His father was an Episcopalian minister.

1880: graduated from Trinity College at Port Hope, Ontario at the age of 14

1881: began teaching math at Bishop’s College in Lennoxville, Quebec

1884: accepted the position of principal and only teacher at the Whitney Institute in Bermuda, where he met his future wife, Helen May Trott

1886: left for New York City with the intention of working for Thomas Edison. After many applications, he was hired as an assistant tester.

1887: promoted to chief chemist of the Edison Laboratory in East Orange, New Jersey

1890: became chief electrician for Westinghouse Electric in Pittsfield, Massachusetts and, in September, married Helen May Trott of Bermuda. They had one son, Reginald Kennelly Fessenden.

1891: worked as an electrician for the Stanley Company in Pittsfield, Massachusetts

1892: went to Purdue University to become professor of electrical engineering

1893 – 1900: accepted the newly created job of chair of electrical engineering at the Western University of Pennsylvania

1900 – 1902: worked with the U.S. Weather Bureau, on the understanding that the Bureau could have access to any devices he invented but that he would retain ownership.

1901: coined the term “Heterodyne” from the Greek heteros (other) and dynamis (force).

1902: awarded the first patent for a “heterodyne receiver” (#706740)

1902: With the backing of two wealthy Pittsburgh businessmen, Hay Walker and T.H. Given, Fessenden formed the National Electric Signaling Company (NESCO)

1906: performed the first AM radio broadcast from Brant Rock, Massachusetts on December 21

1909: Alexanderson and General Electric delivered a 2,000 watt, 100 khz alternator to Fessenden. Using a single rotor disc and iron armature core, it became the model for the larger and more powerful alternators of the future.

1911: Fessenden left NESCO and sued for breach of contract. In 1912 he was awarded $400,000 in damages.

1915: perfected his “Fathometer,” an early sonar device for measuring ocean depths and finding submerged objects

1921: awarded the Medal of Honor by the Institute of Radio Engineers

1922: awarded the John Scott Medal

1925: filed a $60,000,000 antitrust suit against the “Radio Trust” of RCA, GE, Western Electric, United Fruit, AT&T, Westinghouse, and The Wireless Specialty Apparatus Company.

1928: initially awarded $2,500,000 for the “Radio Trust” lawsuit, he eventually settled for $500,000. As part of the settlement, it was agreed that he would be named “The Father of Modern Radio.”
His home address at the time was listed as 45 Waban Hill Road, Newton, Massachusetts.
The home (in the Chestnut Hill district of Newton) is on the National Register of Historic Places.

1929: awarded the Scientific American Medal for Promoting Safety at Sea for his “Fathometer”

1932: Reginald Aubrey Fessenden died on July 22 at his vacation home by the sea in Hamilton, Bermuda. He was interred in the cemetery of St. Mark’s Church on the island.

On the stone lintel across his grave reads the inscription:

“By his genius distant lands converse and men sail unafraid upon the deep.”

Below that line, Egyptian glyphs proclaim: