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History of detectors
Heinrich Hertz
1886
spark gap
~100V
Eduard Branley
1890
coherer
~10V
Jagdish Chandra
Bose 1894
PbS crystal
~0.1V
John Ambrose
Fleming 1904
thermoionic
diode ~0.3V
Armstrong +
Meissner 1912
regenerative
RX ~1mV
Edwin Armstrong
1922
super-regen.
RX ~1μV
Guglielmo
Marconi 1902
magnetic
det. ~1V