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The early days of radio:

Excerpts from JA Fleming's "An Elementary Manual of  Radiotelegraphy and Radiotelephony" (1919 edition), published by Longmans.

‘The future of electricity is absolutely beyond the realm of imagination’
Dr JA Fleming, FRS

Early Detection Systems
A comprehensive overview of the different systems devised in the late 19th and early 20th century to detect radio signals. They range from the famous "coherer" detector, through early valves and lesser-known varieties such as electrolytic detectors, to those reliant on "the curious property of unilateral conductivity"!
The Fessenden "heterodyne telephone"
Three methods of detecting morse signals ranging from the relatively crude but ingenious "tikker" and tonewheel, to Fessenden's hetrodyne technique, which today would be described as "direct conversion":
A detailed outline of a Northumberland radio station (see illustration above), which used both spark and Poulsen Arc transmitters.
Induction Coils