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Researches in radio telephony (1919) (14570292350)


Researches in radio telephony (1919) (14570292350)



Identifier: researchesinradi00petz (find matches)
Title: Researches in radio telephony
Year: 1919 (1910s)
Authors: Petzing, Erwin Walter
Contributing Library: Paul V. Galvin Library, Illinois Institute of Technology
Digitizing Sponsor: CARLI: Consortium of Academic and Research Libraries in Illinois

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been found that this radiation con-sists of nerative electrons and that the numberof electrons emitted increases very fast as the temperature of the hot cathode increases until apoint of saturation is reached. This point isdetermined by the dimensions of the tube. If the plate is kept at a positive potentialthese electrons emitted will be dravm towardsthe plate and a current v;ill b3 set up in thisplate circuit. See firure 2. The current inthis circuit v;ill ba found to vary as the voltarreand can be expressed by the following equation: 2 3 6 -L o i = 14.65(10 ) - e where i = The current in the plate circuit inamperes. L =^ The lenrth of the filament in centimeters. r = The radius of the cylinder. Mr. Saul Dushman of the General Electric Com-pany found that the ionic discharge from the hotcathode increased from about .14 ampere per squarecentimeter at 2,300° absolute to .36 amperes at2,400° to .?9 amperes at 2,500 and to 2.04 amperesat 2,600°; but at hi.rh temperatures the filament
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deterioration is quite rapid. Some idea of the rapidity of increase of thecurrent as the voltage is increased can be rottenlij looking at Fi-ure 1. The current from A to Bconforms very closel;, \.ith the curve gotten hjplotting the above equation for different valuesof e; v.rhen L and r are some definite values irhichare kept constant as e is varied. The dotted curve A, L, E, F is the curve fora lower filament current and consequently a lowerfilament temperature. There is also another current lim.itation v/hichmay prove very serious in practice in high vacuumtubes. This is the so-called space charge anddepends on the following considerations. If theplate voltage has a given value, increase of fila-ment temperature will increase the plate currentto a point B, Fi.gure 3, but no futher. This isdue to the following e/fect: The clouf. of negativeelectrons surroundin- the filament at any time actsas a large negative charge in its neighborhood, andconsequently repels all electrons vAich are,researchesinradi00petz





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