Skip to main content

Voice Over Radio

Fall 2010 | Volume 25 |  Issue 3

In 1900 the United States Weather Bureau hired 34-year-old electrical engineer Reginald Fessenden to develop a wireless system that could distribute forecasts and relay meteorological data. The Canadian-born inventor, a protégé of Thomas Edison, former consultant for Westinghouse, and professor at Purdue and Western universities, moved his family to Spartan accommodations at the Weather Bureau station at Cobb Island, Maryland, 60 miles southeast of Washington, D.C., in the Potomac River. After a year of hard work, Fessenden and his assistants had succeeded in transmitting Morse code 50 miles to Arlington, Virginia.

He also pursued the more difficult task of transmitting sound. His first efforts used the same “spark-gap” equipment that he and others were developing for wireless telegraphy. By operating at a higher frequency and improving the sensitivity of the components, Fessenden understood that he could transmit almost continuous waves (instead of dot-dash signals) and reproduce them in the receiver. The result would be a rapidly varying electric current that would duplicate the original sound when heard through telephonic headphones. On December 23, 1900, as darkness fell and a light snow dusted Cobb Island, Fessenden succeeded in making the first radio transmission of voice ever, sending a signal between two 50-foot-high wooden masts a mile apart.

In hopes of improving his wireless telephony apparatus, Fessenden looked for something to replace the coherer, a detector of electromagnetic waves that was part of all early radio setups. The coherer amounted to a tube of metal filings inserted within a circuit. If no radio waves were present, the filings were randomly oriented and had a fairly high resistance. But when the coherer was acted upon by a wave, the filings lined up and completed the circuit. The coherer worked better than any other wave detector, but it had numerous deficiencies, not the least of which was that it had to be tapped with a vibrator to decohere the filings.

Fessenden replaced the coherer with what he called a barretter, a very thin piece of wire. A radio wave induced a current in the wire, heated it, and increased its resistance. This “hot-wire” barretter, which took form during 1901, was no more sensitive than the coherer, but because it lacked the coherer’s on-or-off nature, it could reproduce speech much more efficiently.

Long-distance wireless telephony, however, required a more sensitive detector. He found an answer by accident in 1902 when he broke a barretter while cleaning it in nitric acid. Surprisingly, the broken wire worked much better than a whole one. He then designed a detector incorporating two extremely fine platinum wires whose ends were dipped into a pool of acid.

Though it required frequent maintenance, Fessenden’s “liquid barretter” proved successful, soon enabling him to broadcast musical notes between Roanoke Island and Hatteras. As word of his accomplishments spread, various U.S. and Mexican government agencies began placing orders for his apparatus.

In 1905, now president of his own company, National Electric Signaling Company, he built a 400-foot-high cylindrical tower in Brant Rock, Massachusetts, and another in Machrihanish, Scotland. On January 10, 1906, he oversaw the world’s first successful transatlantic wireless two-way transmissions. Night is the best time for sending radio signals, but atmospheric conditions made it impossible to exchange successful transmissions every night, and as the days grew longer, the signals began to fade. Finally transatlantic communications had to be abandoned, not to be resumed until October.

By that time, Fessenden had taken another great step. For years he had realized that the key to achieving greater clarity in transmission of both telegraphy and telephony lay in the use of higher frequencies. At 60 cycles per second, ordinary wireless signals created vibrations that made telegraph clicks difficult—and voices nearly impossible—to hear. Increasing the frequency of the signal above the range of human hearing could greatly reduce this problem.

Fessenden’s plan required a means of converting audible signals into higher-frequency electromagnetic waves, transmitting them, and then converting them back to sound at the receiving end. His heterodyne principle worked on the idea that if two vibrations are created simultaneously, additional vibrations, or beats, will be heard at the sum and difference of their frequencies. He would send out a high-frequency signal that was modulated—varied slightly in frequency—by a speaker’s voice. That signal would be mixed with another signal of the same high frequency, except that this one would be held constant. The two signals would differ by the amount of the modulation—in other words, by the frequency of the sounds being transmitted. Therefore, the beat frequency, equal to the difference of the two, would reproduce the voice that had modulated the original signal.

On December 21, 1906, reporters listened as Fessenden established voice transmission with a fishing boat. Then, on Christmas Eve, the inventor made history’s first public radio broadcast. Intended for ships at sea, it consisted of the playing of a recording of Handel’s “Largo”; Fessenden himself performing “O Holy Night” on the violin and singing the last verse; a Bible reading; and finally Fessenden wishing everyone a Merry Christmas. “I had not picked myself to sing,” the inventor later explained, “but on Christmas Eve I could not get any of the others to either talk, sing or play, and consequently had to do it myself.” Ships equipped with Fessenden’s apparatus had been told several days earlier to listen for the broadcast.

Fessenden had named his principle after the Greek word for “different power.” It proved so simple and effective that it is still in use today. In 1905, however, when Fessenden patented the system, it was way ahead of its time. Anyone receiving the signal would need an expensive and finicky apparatus to generate a matching frequency. It would take the addition of Lee De Forest’s vacuum tube, which was integrated with Fessenden’s principle in Edwin H. Armstrong’s “superheterodyne” system of 1912, to make voice transmission reliable enough for widespread use.

On the heels of a century that saw wireless progress from the dots and dashes of Morse code to the 0s and 1s of the Internet, the magnitude of Fessenden’s achievements appear quite farsighted and support his own definition of an inventor as “One who can see the applicability of means to supply demand five years before it is obvious to those skilled in the art.”

We hope you enjoyed this essay.

Please support America's only magazine of the history of engineering and innovation, and the volunteers that sustain it with a donation to Invention & Technology.


Stay informed - subscribe to our newsletter.
The subscriber's email address.