1904

Alexanderson alternator

• Before 1904, many inventors, including Nikola Tesla,
• created an alternator to generate an electromagnetic frequency,
• but none of these produced a frequency high enough
• for radio transmission; they were all under twenty kilohertz.
• However, in 1904, Reginald Fessenden, working for
• National Electric Signaling Company, contracted with GE
• for an alternator to produce up to a hundred kilohertz
• for continuous wave radio transmission.
• Ernst Alexanderson designed an alternator whose frequency
• was controlled by a rotor with hundreds of narrow slots
• that caused a variable reluctance to interrupt the flux,
• which induced a radio-frequency voltage in a set of coils.

Transoceanic broadcasts

• The Alexanderson alternator allowed the installation
• of broadcast stations around the world for broadcasting transoceanic
• high-power longwave radiotelegraphic messages in Morse code,
• which became an urgent requirement during World War I.

Alexanderson Day

• The Varberg Radio Station
• near Grimeton, Sweden,
• celebrates Alexanderson Day
• by broadcasting Morse
• code messages on 17.2 kHz
• using the last working
• Alexanderson alternator.

The box

• People thought
• you needed
• a spark-gap transmitter
• to make radio waves.
• Today we call that
• thinking inside the box.