In article , Alun
writes:

Fessenden demonstrated voice modulated spark operation as early as
1900. His methods have been verified by actual tests using replica
transmitters and dummy loads.

Fessenden transmitted voice over one mile during December 1900, possibly
on the 12th, on Cobb Island, Maryland.

Yep. You can even listen to re-creations of what it may have sounded like
on-line. I posted the urls here some time back.

By 1903, he had reached 50 miles.

Of course in a way *almost all* spark transmitters use alternators, because
except for simple spark coils, they *all* use AC generated by alternators...

Fessenden's innovation was to use AC above the voice frequency range.

Brilliant guy. Over 500 patents, in a variety of fields.

Fessenden had a two-way transatlantic radiotelephone setup in operation
by November of 1906 using alternator RF sources.

The demo of Christmas Eve 1906 was repeated a week later (New Year's
Eve).

These events are well documented.

As is DeForrest's later voice coverage of the New York yacht race, using a
spark transmitter of the earlier type (no alternator) but using a
regenerative detector with a triode tube. I can't remember when that took
place, although it is in several books, but the triode (audion) patent
discloses the regenerative detector and was issued in 1907, so the yacht
race must have taken place around that period.

Practical regenerative detection is generally credited to Armstrong in 1915.
However, DeForest's use of voice communication at such an early date is another
historic fact.

Seems to me that Fessenden's transatlantic 2 way radiotelephone operation is
the most significant of these early developments. Less than 5 years after
Marconi claimed one-time one-way reception of a single coded letter, Fessenden
had practical, repeatable, two-way voice transatlantic radio communications
over a longer path, using much less power.

73 de Jim, N2EY