I’m Positive You Will Not Know What This Is. Go Ahead And Prove Me Wrong (If You Can)
These basic radios used no battery, had no amplification and could operate only high-impedance headphones.
They would receive only very strong signals from a local station.
They were popular among the less wealthy due to their low build cost and zero run cost.
Crystal sets had minimal ability to separate stations, and where more than one high power station was present, inability to receive one without the other was a common problem.
Electromagnetic waves were predicted by James Clerk Maxwell in his 1873 theory of electromagnetism, now called Maxwell’s equations, who proposed that a coupled oscillating electric field and magnetic field could travel through space as a wave, and proposed that light consisted of electromagnetic waves of short wavelength. On November 11, 1886, German physicist Heinrich Hertz, attempting to confirm Maxwell’s theory, first observed radio waves he generated using a primitive spark gap transmitter.[4] Experiments by Hertz and physicists Jagadish Chandra Bose, Oliver Lodge, Lord Rayleigh, and Augusto Righi, among others, showed that radio waves like light demonstrated reflection, refraction, diffraction, polarization, standing waves, and traveled at the same speed as light, confirming that both light and radio waves were electromagnetic waves, differing only in frequency.[20] In 1895, Guglielmo Marconi developed the first radio communication system, using a spark gap transmitter to send Morse code over long distances. By December 1901, he had transmitted across the Atlantic ocean.[4][5][6][7] Karl Ferdinand Braun invented the phased array antenna in 1905. Three antennas are arranged to transmit a directional signal.[21] Marconi and Braun shared the 1909 Nobel Prize in Physics “for their contributions to the development of wireless telegraphy”.[22]
During radio’s first two decades, called the radiotelegraphy era, the primitive damped wave radio transmitters could only transmit pulses of radio waves, not the continuous waves which were needed for audio modulation, so radio was used for person-to-person commercial, diplomatic and military text messaging. Starting around 1908 industrial countries built worldwide networks of powerful transoceanic spark transmitters to exchange telegram traffic between continents and communicate with their colonies and naval fleets. During World War 1 the development of continuous wave radio transmitters and rectifying electrolytic and crystal radio receiver detectors enabled amplitude modulation (AM) radiotelephony to be achieved by Reginald Fessenden and others, allowing sound (audio) to be transmitted. On November 2, 1920, the first commercial radio broadcast was transmitted by Westinghouse Electric and Manufacturing Company in Pittsburgh, under the call sign KDKA featuring live coverage of the Harding-Cox presidential election.