. Elements of radio telephony . a minimum. Tube Detectors.—The tube detector was theso-called Fleming Valve and consisted only of hot fila-ment and cold plate. Its action was merely that of a rec-tifier as has been described in a preceding chapter and ittook the place of the crystal detector. Since it was no moresensitive than a crystal detector and reqiiired auxiliary bat-teries, for its operation, it never became very popular andhence will not be considered here. The three-electrode tube, however, is in almost universaluse where the distances to be covered are great, and a sen-s
. Elements of radio telephony . a minimum. Tube Detectors.—The tube detector was theso-called Fleming Valve and consisted only of hot fila-ment and cold plate. Its action was merely that of a rec-tifier as has been described in a preceding chapter and ittook the place of the crystal detector. Since it was no moresensitive than a crystal detector and reqiiired auxiliary bat-teries, for its operation, it never became very popular andhence will not be considered here. The three-electrode tube, however, is in almost universaluse where the distances to be covered are great, and a sen-sitive detector is desired. A typical connection is shownin Fig. 33, here the circuit that was formerly connected to 68 ELEMENTS OF RADIO TELEPHONY the crystal detector and telephones is now connected betweenthe grid and the filament of the detector tube. - The internal action of the vacuum tube has been discussedin a preceding chapter. There are two general explanationsof the detector action in a vacuum tube, one when a con-. FiG. 33.—Non-regenerative vacuum-tube detector set. ■denser is used in the grid circuit, the other without the gridcondenser. Referring to Fig. 33 let Ec be the voltage inducedacross the terminals of the condenser C2 due to the incomingsignal. Represented graphically it might look something Hkethe wave marked Ee in Fig. 34. If we consider the positiveparts of the waves as being above the line, and those below RECEIVING EQUIPMENT 69 negative, then when the grid voltage is positive a currentwill tend to flow in the grid circuit while no current will passwhen the grid is negative. These pulses of current passinginto the grid condenser on their passage through the gridcircuit will charge it up so that it will produce a negative CofK/enser /o/h7^e /IJL A\L Al ^.^ - ^— ^^—^ ^ A/e^af^i\i>e qndvottaqe. T^hphone current.
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectradio, bookyear1922
