. Elements of radio telephony . Grid Vottage^nege/fiVe O positive — Fig. 36.—Grid voltage-plate current curve for a soft detector tube. both these functions are present when using a grid con-denser. Soft Tubes.—Tubes that have an appreciable amount ofgas left in them seem to make better detectors than thosewhich are thoroughly exhausted, and this increased sensibilitycan best be explained by considering the relation between platecurrent and grid voltage in each case. Fig. 35 shows therelation between these quantities for a hard tube or one RECEIVING EQUIPMENT 73 in which the vacuum is very goo
. Elements of radio telephony . Grid Vottage^nege/fiVe O positive — Fig. 36.—Grid voltage-plate current curve for a soft detector tube. both these functions are present when using a grid con-denser. Soft Tubes.—Tubes that have an appreciable amount ofgas left in them seem to make better detectors than thosewhich are thoroughly exhausted, and this increased sensibilitycan best be explained by considering the relation between platecurrent and grid voltage in each case. Fig. 35 shows therelation between these quantities for a hard tube or one RECEIVING EQUIPMENT 73 in which the vacuum is very good and practically no gaspresent. Fig. 36 shows the same relation for a soft tubein which the vacuum is not quite so high and a small amountof gas remains. The sudden rise in plate ciurent when thegrid is made positive is due to ionization of the gas par-ticles in the tube. The effect of ionization is to produce newelectrons from the gas molecules and thus greatly increase. Fig. 37.—One type of soft or gas content deteetor tube. the plate current whenever the grid voltage (or plate voltage)is brought above a critical value. This phenomenon iscalled ionization by collision and may be explained inthe following manner. In a tube from which all gas hasbeen exhausted and whose vacuum is very high, the elec-trons are unimpeded in their passage from the filament tothe plate or grid. In tubes in which traces of gas remain thisis not the case for according to the modern theory of gasesnumerous molecules of gas are constantly darting back and 74 ELEMENTS OF RADIO TELEPHONY forth inside the tube. A gas molecule ordinarily comprises aminute portion of gas, an electron or negative charge and anequal and opposite positive charge. These two charges areof equal value and opposite, polarities so that their net effectis to make the molecule electrically neutral. As the elec-trons move from filament to plate some of them naturallycollide with some of the gas molecules. T
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectradio, bookyear1922
