Trials & Errors #69: The Man Behind AM Radio

Some people get all the publicity . . . like Guglielmo Marconi, for example. Others, like Reg Fessenden, struggle a bit "behind the scenes" due to a much different personality. But both types of inventors have added to our radio interests tremendously. This is the forum discussion for the story of Reginald Fessenden, the inventor of Continuous Wave CW and AM Radio. Read the article at this link and comments below, please! Dave, W7DGJ

 

Fessenden used not only his own talents, but also relied on other great minds. In this particular project the key feature was the design of
the high-frequency alternator transmitter by Ernst Alexanderson who was a disciple of the great Charles Proteus Steinmetz.

Fessenden commissioned General Electric to design and build a workable alternator, and the assignment went to the young Alexanderson. He was able to find solutions to both the electromagnetic and dynamic structural mechanics problems inherent in such devices.

Previously, Fessenden had tried to use spark transmitters with very high spark rates to create the carrier, but had to abandon these attempts due to implementation difficulties.

In 1906, the only continuous-wave transmitter available was the alternator, as the practical Poulsen arc generator was still a few years in the future.

 

I recently read a biography of Marconi, and my perception of him of changed a lot. Neither a scientist or engineer...a bit like Edison. We can thank the Guinness fortune for giving him a start in business.

Now I am going to find a biography of Fessenden. Any suggestions?

 

Many of these great inventors were "marketers" just a few steps behind those guys selling miracle oil on pony carts. Marconi and Fessenden, and Edison, all had a genius that others may not possess, but both Marconi and Edison were masters of the media. Dave, W7DGJ

 

Here's his official family biography written by his wife, Helen. Dave W7DGJ https://www.worldradiohistory.com/B...omorrow-Fessenden-1940.pdf#search="fessenden"

 

"The Irish Connection"

 

Fessenden was deeply involved in underwater acoustics and signaling. He worked with Submarine Signal Company to develop ways to send sounds and detect them underwater, starting with bells under lightships. Here is the longer story:
https://archive.navalsubleague.org/...radar-submarine-signal-company-1901-1946-part

 

Thanks Gary. I mentioned some of his other patents, ie the above, in my article, which was primarily focused on the man's accomplishments in radio. Dave, W7DGJ

 

Nice job!

Fessenden did not 'invent' heterodyning. It was already a well known wave phenomenon. He did produce 'method and apparatus' for same at RF, as syntony took over the airwaves.

 

The heterodyne phenomenon was known in acoustics and wave physics since at least the mid-19th century.
Lord Rayleigh was one of the pioneers of describing mixing and heterodyning in a mathematical-physical context.

 

Fessenden used the heterodyne principle to make CW signals audible.

At about the same time, Alexanderson proposed a telephone repeater, which used alternators, heterodyning and magnetic amplifiers to create an early carrier-based telephone multiplex system.

 

Hence my comment. 'Syntony' is a tuned tone. That is, CW not raspy- noise spark.

 

Yep.

 

Marconi, and his predecessor Lodge, used the term"syntony" to describe the use of resonant circuits for narrowing the transmitted spectrum and create emissions with a somewhat defined centre frequency.
But the emissions were not single-frequency or coherent.

Further work by Rendahl and von Arco at Telefunken led to the development of "Tönende Löschfunken" or "quenched gap emissions", which were even narrower but still not coherent by any means.

 

Now I know what it'd feel like if Irony died and came back from the dead reincarnated as Charlie McCarthy wielding Edgar Bergen as the dummy and despite my best efforts I couldn't tell who was doing the talking.