. The thermionic vacuum tube and its applications . ven in Section 53 that the intercept OA which represents the negative grid potential necessaiy to reduce -pithe plate current to zero is —. If we now apply a constant jp grid potential Eg= ^ and make the peak value of the low fre-2/i quency input voltage equal to this quantity, then the amplitude of the high frequency oscillations is reduced to zero every time that the grid acquires its maxmium negative potential CA and then the wave will ])e completely modulated. The simplest way to secure this in j^ractice is first to adjust the negative gr
. The thermionic vacuum tube and its applications . ven in Section 53 that the intercept OA which represents the negative grid potential necessaiy to reduce -pithe plate current to zero is —. If we now apply a constant jp grid potential Eg= ^ and make the peak value of the low fre-2/i quency input voltage equal to this quantity, then the amplitude of the high frequency oscillations is reduced to zero every time that the grid acquires its maxmium negative potential CA and then the wave will ])e completely modulated. The simplest way to secure this in j^ractice is first to adjust the negative grid battery DETECTION OF CURRENTS WITH THE VACUUM TUBE 343 E F in the input circuit of the modulator to a vakie —-\--^; that is, to a value given bj^ OD (Fig. 204), and then gradually increasethe strength of the low frequency input voltage until a d-c. meterplaced in the output of the modulator just indicates a currentflow in the output of the modulator. The peak value of the input potential is then ecjual to DA or ?^. The voltage of the high. Fig. 205. fiequency impressed on the modulator can also be measured inthe same way and should in general be somewhat smaller than thelow frequency voltage. Finally the grid battery in the inputcircuit of the modulator is adjusted to the value OC, before themeasm-ements on the detecting current are undertaken. Fig. 205 shows some experimental results that were obtainedwith the circuit shown in Fig. 203. The ordinates indicate thesetting of the receiver shunt for different values of the input volt-age eg, the logarithms of which are plotted as abscissa. Accord- 344 THERMIONIC VACUUM TUBE ing to equation (32) these points should he on a sta-aight , if equation (31) holds the slope of this Hne should be2K; that is, , since K for the leceiver shunt used is crosses and circles represent observations made by two dif-ferent observers on different days. The slope of the hne drawnthrough them is Thes
Size: 1688px × 1480px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1920, bookidthermionicva, bookyear1920
