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ALEXANDERSON ALTERNATOR

Notes:

Perhaps the first real generation of a sinusoidal continuous waves was by RA Fessenden, in the USA, with the use of a high frequency alternator.

This was the first time the words ‘high frequency’ seem to have been used although the highest carrier frequency produced was around 100kHz. It was keyed by varying the current in the field windings.

Here we see the ultimate development of Fessenden’s transmitter, the 200 kW Alternator developed by Dr Ernst Alexanderson, shown here at the Marconi station near Caernarfon in North Wales.

Fortunately, one of these remains preserved in operating condition in Sweden and comes on the air from time to time. For those unable to receive 17.2 kHz this is what it sounds likes.
The limitation on radio communications may have been the electrical nature of the equipment, but an incomplete understanding of radio propagation in those early days also indicated that the radio spectrum was unreliable or virtually useless above 3 MHz.