Spark gap transmitter were (one of?) the first form of radio broadcasting: https://en.wikipedia.org/wiki/Spark-gap_transmitter https://en.wikipedia.org/wiki/Spa

Spark gap transmitter were (one of?) the first form of radio broadcasting: https://en.wikipedia.org/wiki/Spark-gap_transmitter https://en.wikipedia.org/wiki/Spark-gap_transmitter . Since it is not very selective - its signal spreads through the whole spectrum - its use is forbidden today; think a single radio station which transmitter over all frequencies, like you can turn the dial and it will always interfere and you can't get rid of it. Because tuning was a known "phenomenon" and having the possibility of using the radio spectrum for multiple transmission was desirable, efforts began to make transmissions more selective so they wouldn't pollute the whole radio spectrum. Radio pioneers didn't have anything close to modern small, powerful, solid state, very close to sine oscillators at the time. They had to use what was available so they could modulate their transmission. In a simplified model, a radio transmission be thought of as an antenna whose electric potential varies with the sine of time at, for AM broadcasts, the order for hundred of kilohertz. This oscillation is then "multiplied" by the signal one want to transmit. Better results occur when the "transmitted signal" (think about it as something close to a payload) has a much lower frequency than the "carrier": the frequency at which the potential of the antenna would oscillate to transmit a constant value. Now, early broadcast really worked around the technology available at the time. To oscillate the electric potential of the antenna, they resorted to eletromechanical methods. Very interesting solutions were developed: https://en.wikipedia.org/wiki/Spark-gap_transmitter#Rotary_gap_transmitters https://en.wikipedia.org/wiki/Spark-gap_transmitter#Rotary_g...