Application Coherer

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the coherer used in practical receivers glass tube, evacuated, half filled sharply cut metal filings, part silver , part nickel. silver electrodes made contact metal particles on both ends. in coherers, electrodes slanted width of gap occupied filings varied rotating tube long axis, adjusting sensitivity prevailing conditions.


in operation, coherer included in 2 separate electrical circuits. 1 antenna-ground circuit shown in untuned receiver circuit diagram below. other battery-sounder relay circuit including battery b1 , relay r in diagram. radio signal antenna-ground circuit turns on coherer, enabling current flow in battery-sounder circuit, activating sounder, s. coils, l, act rf chokes prevent rf signal power leaking away through relay circuit.



a radio receiver circuit using coherer detector (c). tapper (decoherer) not shown.


one electrode, a, of coherer, (c, in left diagram) connected antenna , other electrode, b, ground. series combination of battery, b1, , relay, r, attached 2 electrodes. when signal spark gap transmitter received, filings tend cling each other, reducing resistance of coherer. when coherer conducts better, battery b1 supplies enough current through coherer activate relay r, connects battery b2 telegraph sounder s, giving audible click. in applications, pair of headphones replaced telegraph sounder, being more sensitive weak signals, or morse recorder recorded dots , dashes of signal on paper tape.



a coherer electromagnet-operated tapper (decoherer), built radio researcher emile guarini around 1904.


the problem of filings continuing cling , conduct after removal of signal solved tapping or shaking coherer after arrival of each signal, shaking filings , raising resistance of coherer original value. apparatus called decoherer. process referred decohering device , subject innovation during life of popular use of component. tesla, example, invented coherer in tube rotated continually along axis.


in later practical receivers decoherer clapper similar electric bell, operated electromagnet powered coherer current itself. when radio wave turned on coherer, dc current battery flowed through electromagnet, pulling arm on give coherer tap. returned coherer nonconductive state, turning off electromagnet current, , arm sprang back. if radio signal still present, coherer turn on again, pulling clapper on give tap, turn off again. result constant trembling of clapper during period radio signal on, during dots , dashes of morse code signal.







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