I can somewhat understand how the spark-gap was devised to transmit waves and how the waves were first measured in frequency but what lead to the idea of "modulation" where another electrical signal generated from a voice would be carried on the wave produced by the spark-gap.

Fessenden was I believe the first to demonstrate this by constructing large alternating current spark generators but he would still need to know how to "encode" a wave onto another wave and rectify it in such a way at to both transmit and receive.

I was even wondering if perhaps he was proficient in Fourier analysis or perhaps some other mathematics to figure out how to encode or modulate and demodulate the signal. I am still researching the topic and the more I think about this the more amazing of a feat it seems to be.

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    The alternators built by Fessenden were high-speed machines that generated a high frequency alternating current, that –with a proper antenna– produced electromagnetic waves. Nothing to do with spark oscillators, where current pulses fed a resonant LC circuit tuned to the desired frequency. – xxavier Dec 4 at 9:21
  • thank you for commentary. Is the alternator you refer to produce the "carrier"....if so how did scientists come to realize they could embed intelligence in the form of an electrical signal from a voice which is a much lower frequency and embed the intelligence in the signal from the alternating current. Also I am wondering if the spark oscillator is anther method to modulate the wave perhaps developed after ? – Sedumjoy Dec 4 at 16:29
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    Fessenden used an alternator giving a carrier frequency of 75 kHz, modulated in amplitude by the simple expedient of inserting a carbon mike between one of the alternator leads and the antenna... More info here: ieee.ca/millennium/radio/radio_differences.html – xxavier Dec 4 at 17:32
  • Outstanding article in the link. – Sedumjoy Dec 5 at 1:32

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