Reginald Fessenden & the Physics of the First Radio Broadcast

In 1899, a temperamental Canadian scientist had a vision that speech and music could be sent by wireless.  It took him seven years but in November of 1906, Reginald Fessenden sent wireless music and speech for over 10 miles where “the sound was perfect”.  Ready for the story of how modern radio began?  Let’s go!

Let me tell you a bit about Reginald Fessenden.  Fessenden grew up in Canada but had moved to the US (after a brief stint in the Bahamas) in 1886 when he was 20 to try to work with Edison.  According to Fessenden, Fessenden sent Edison an introduction and Edison responded with a slip of paper that said, “Am very busy.  What do you know about electricity?”  Fessenden honestly replied, “Do not know anything about electricity, but can learn pretty quick,” whereupon Edison spat, “I have enough men now who do not know about electricity”!  Fessenden persevered and got a job burying electrical lines for Edison.  He fondly recalled how difficult it was to get permits and bribes to bury electrical lines and how the “strategy” was “to open a street, replace half a dozen lengths of main and get the street into innocent-looking shape again between police patrols.[1]”  Fessenden quickly moved up the ranks to become Edison’s head chemist.  In 1889, “Fessy” heard about Hertz’s experiments in creating and transferring radio waves.  He asked Edison for permission to study wireless, which Edison agreed to as soon as he returned from the Paris exposition (the same place where Tesla heard of Hertz’s experiments and was inspired to invent the Tesla coil).  However, as soon as Edison returned “the whole laboratory was shut down,[2]” due to financial difficulties, and Fessenden was out of a job!  Fessenden then worked for a while for Edison’s rival George Westinghouse who helped Fessenden get a job as a professor.

Reginald Fessenden
Reginald Fessenden

It was as a professor, in 1898, that he was asked to conduct some wireless experiments.  He declined and told them to ask Marconi, but it started him thinking about wireless again.  He realized that plenty of people was conducting wireless experiments but no one was doing any scientific studies with exact measurements.  The big handicap, he felt, was that at the time the receiver that most people used, a coherer, would stick together (or cohere) in the presence of a radio wave but as it worked as an on-off switch it didn’t work to tell how powerful the radio wave was.   

Fessenden started to play with different receivers that would create a variable resistance with the strength of the radio wave.  One of these systems induced a voltage in a secondary wire with a telephone speaker attached that would beep.  Fessenden used a transmitter that made a “peculiar wailing sound”.  He was astonished to find that when someone hit the long dash on the telegraph that sound “was reproduced with absolute fidelity in the receiving telephone. [3]”  Fessenden was instantly convinced that he could transmit sound wirelessly – or make a wireless telephone.    

At the time, the system to create radio waves was called a spark gap generator and would create a pulse of radio waves and a spark a number of times every second (usually around 20-50).  Fessenden’s friend created the blueprints for a transmitter that made 10,000 radio pulses per second so that it would create basically continuous (although uneven) pulses of radio waves.   By the end of 1900, it was complete and Fessenden attached a microphone to the transmitter so that when a person talked into the microphone it compressed or extended the carbon fibers in it to change the resistance and thus the amplitude (or strength) of the current.  Because this system modulated the amplitude it was eventually called AM radio (for Amplitude Modulation).  He managed to send a signal for over a mile, however, it created what was to him an, “extremely loud and disagreeable noise, due to the irregularity of the spark.[4]”  What Fessenden needed was a better way to make smooth continuous radio waves, so he created one.

Fessenden and the Early History of Radio Science

In 1904, Fessenden worked with General Electric (no Edison anymore) to create an AC generator that would make smooth continuous waves at 100,000 Hz.  The idea was to create AC current the same way a generator does (spinning wires near electromagnets) but spin it ridiculously fast and have as many magnets as possible.  Instead of using complicated coils, they created a solid metal disk with radial slots in it filled with a non-conducting material.  It was a major project.  They hired a 26-year-old Swedish-American engineer named Ernst Alexanderson and two years later, in 1906, they finally succeeded.  The Alexanderson alternator was the finest radio wave producer in the world.  However, it was also the size of a car and significantly more expensive.

In the meantime, Fessenden also created a better receiver than made radio waves audible, called an electrolytic receiver.  See, if you have an antenna you can “catch” radio waves.  If you add a capacitor which is an object that has two conductive sides with a thin insulator between them the capacitor can collect charges on the surfaces.  If a capacitor discharges through a coil, it will create a changing current and a magnetic field in a coil, which creates more current in the coil, which then charges the capacitor in the other direction, which will then discharge the other way.  What I’m trying to say here is if you have a capacitor and a coil it will tend to oscillate, this is called a tank circuit and is the backbone of all radio.  Therefore, if you have an antenna with a coil and a capacitor then you can tune your coil so that it vibrates at the same frequency as the incoming wave.  However, if you placed the signal in a speaker it would oscillate way too fast for a human to hear.  What he needed was a one-way valve or a rectifier. If you then listened to the signal on headphones, the headphones would only respond to the envelope – or the uneven amplitude of the signal.  So, the big question is, how do you make a one-way electrical valve?

Fessenden created his best one-way valve in 1903.  Fessenden’s “detector” had a thin piece of platinum in a cup of acid that was connected to a battery with a variable resistor.  The resistor would be adjusted to give a tiny bit of voltage across the detector, which would create a reaction between the acid and the metal and would create an insulating bubble around the metal.  If a separate voltage was placed in the same direction then the bubble would increase in size and no current could flow.  If the voltage was in the opposite direction then the bubble would decrease and the current could then flow.  Voila, a one-way valve.  For a few years, this detector was the most popular radio detector around.

Reginald Fessenden, an electrical engineer, broadcast the first audio over radio 115 years ago

So now Fessenden had a way of creating a smooth radio wave and modulating the amplitude with sound and a way to listen to it in a receiver, it was time to build a giant radio tower and send the first, true AM radio signal.  On December 10, 1906, they sent out invitations to scientists and local newspapers to witness history and wireless transmission of sound over 10 miles!  They spoke and played records and even surprised a fisherman on a boat (who was expecting the beep of Morse code, not audible speech). 

Fessenden also later claimed that he created a whole musical selection for the enjoyment of people on a boat on Christmas eve, 1906, but there is much contention about whether that actually happened or not.  Even if it did, however, Fessenden wasn’t thinking about broadcasting radio signals, he was thinking about making a wireless telephone.  Also, Fessenden began to fight with his coworkers and in 1911 was fired from his job (he was known for his temper, famously telling an assistant, “Don’t try to think.  You haven’t got the brains for it.”[5]).  Fessenden then stopped working on wireless altogether.  

In fact, almost no one was thinking about broadcasting music and news to a box before 1920.  But there was one man who did dream of modern radio broadcasting way back in 1908.  His name was Lee de Forest, and after reading about Fessenden’s “wireless telephone” system he decided to create a wireless telephone company.  DeForest said that with “his” radio system, “the opera may be brought into every home.  Some day the news and even advertising will be sent out to the public over the wireless telephone.”[6] He also dreamed that people could gather in a “large salon” and with a “huge receiver” people could, “hear the music simultaneously.[7]”  DeForest was a visionary, but he also stole most of his devices.  How this con artist accidentally transformed our world is next time on the secret history of electricity.


[1] P 2274 Radio News “The Inventions of Reginald Fessenden” June 1925

[2] p 237 Radio News “The Inventions of Reginald Fessenden” Aug 1925

[3] “Fessenden, “Wireless Telephony” Transactions of the American Institute of Electrical Engineers, Vol. 28 June 29, 1909 p. 579

[4] Fessenden, Reginald “Wireless Telephony” Transactions of the American Institute of Electrical Engineers, Vol. 28 June 29, 1909 p. 570

[5] p 9-10 “Wireless Radio: A History” Coe

[6]quoted in Homer, Rene “The New Wireless” Universal Engineer Vol. 8-9 January 1909 p. 346

[7] P. 107 Radio News “The Life and Works of Lee deForest” July 1925

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